| 1. |
- Antonsson, Tomas, et al.
(author)
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Liquid Ni-Fe penetration and recrystallisation in tungsten
- 2003
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In: International journal of refractory metals & hard materials. - 0263-4368. ; 21:3-4, s. 159-170
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Journal article (peer-reviewed)abstract
- Melt penetration in grain boundaries of solid tungsten has been investigated. Solid tungsten rods have been exposed to a nickel-iron melt saturated with tungsten and the penetration depth and the shape of the liquid channels have been examined. The solid tungsten samples have been treated in different ways like cold working, annealing and recrystallisation, before melt exposure. Important parameters for the penetration process are stresses, surface tensions, solution and kinetic effects. A new theoretical model for the penetration mechanism in cold worked samples is proposed. Rapid recovery of the grains in the penetrated areas of the cold worked samples was observed. This is discussed, as well.
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| 2. |
- Frykholm, R., et al.
(author)
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Effect of cubic phase composition on gradient zone formation in cemented carbides
- 2001
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In: International journal of refractory metals & hard materials. - 0263-4368. ; 19:06-apr, s. 527-538
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Journal article (peer-reviewed)abstract
- Cemented carbide cutting tool inserts with a surface zone depleted of hard cubic carbides and enriched in ductile binder phase have been studied experimentally using scanning electron microscopy (SEM), electron probe micro analysis (EPMA) and transmission electron microscopy (TEM). The results are compared with simulations based on a solution of the multicomponent diffusion equations, coupled with calculations using thermodynamic descriptions of the individual phases. The materials in the study are based on WC-Ti(C,N)-Co, WC-Ti(C,N)-NbC-Co and WC-Ti(C,N)-TaC-Co. The surface zone is formed by creating a gradient in nitrogen activity in the material, leading to an outward diffusion of N. Due to thermodynamical coupling between N and Ti, the outward diffusion of N will lead to an inward diffusion of Ti, and a surface zone depleted in cubic carbides is formed. Additions of elements like Ta or Nb will affect the width of the surface zone. A material with a Ta-containing cubic phase will have a narrower surface zone than a material with a Nb-containing cubic phase. Ta or Nb additions also affect the distribution of the different phases in and adjacent to the surface zone.
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| 3. |
- Hugosson, Håkan Wilhelm, et al.
(author)
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The connection between the electronic structure and the properties of binderless tungsten carbides
- 2003
-
In: International journal of refractory metals & hard materials. - 0263-4368. ; 21:02-jan, s. 55-61
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Journal article (peer-reviewed)abstract
- Using first principles density functional calculations, we here connect the physical properties of binderless tungsten carbides with the theoretical electronic structure as calculated from density functional theory calculations. We show that electronic structure calculations predict and explain various known phenomena in these systems, an example of how such theoretical studies can be a valuable tool in materials science. For example, changes in the energy of formation from 25% substitution with Mo or Ti is used to explain the differences in intermixing between binderless tungsten carbides using TiC or Mo2C as gamma binder phase. Substitutions with Ti atoms are also predicted to stabilize tungsten carbide in the NaCl-structure. A study of the charge density redistribution after substitution is also made.
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| 4. |
- Hugosson, Håkan Wilhelm, 1972-, et al.
(author)
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The connection between the electronic structure and the properties of binderless tungsten carbides
- 2003
-
In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 21:1-2, s. 55-61
-
Journal article (peer-reviewed)abstract
- Using first principles density functional calculations, we here connect the physical properties of binderless tungsten carbides with the theoretical electronic structure as calculated from density functional theory calculations. We show that electronic structure calculations predict and explain various known phenomena in these systems, an example of how such theoretical studies can be a valuable tool in materials science. For example, changes in the energy of formation from 25% substitution with Mo or Ti is used to explain the differences in intermixing between binderless tungsten carbides using TiC or Mo2C as γ binder phase. Substitutions with Ti atoms are also predicted to stabilize tungsten carbide in the NaCl-structure. A study of the charge density redistribution after substitution is also made.
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| 5. |
- Zhang, Z. Y., et al.
(author)
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The reduction of cobalt doped ammonium paratungstate to nanostructured W-Co powder
- 2002
-
In: International journal of refractory metals & hard materials. - 0263-4368. ; 20:3, s. 227-233
-
Journal article (peer-reviewed)abstract
- Cobalt doped ammonium paratungstate (Co-doped APT) precursors for the fabrication of cemented carbides were synthesized by co-precipitation, where W and Co are mixed on the atomic scale. The effect of cobalt content on the reduction of W-Co precursor was studied. W-Co precursors with different ratios of tungsten to cobalt were prepared and calcined at 220 degreesC for 5 h in air, followed by a reduction in hydrogen gas at 600 and 650 degreesC for different times. The resulting powders were characterized with respect to phase constituent, specific surface area, particle size, density, and morphology of the reduced powders. It has been found that the addition of cobalt results in a higher reduction rate toward the metallic phases. However, the particle size of the reduced powders increases with increasing cobalt content, while its relative density decreases. The specific surface area of reduced powders at 650 degreesC increases for short reduction times, due to reduction of oxides to metal powder, and decreases for long reduction time due to agglomeration of metal powder. Cobalt plays the role as a catalyst during the reduction processing. On the other hand, it promotes the agglomeration of small particles. However, the completely reduced powders were well nanostructured with an average particle size between 20-50 nm.
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| 6. |
- Akhtar, Farid
(author)
-
An investigation on the solid state sintering of mechanically alloyed nano-structured 90W--Ni--Fe tungsten heavy alloy
- 2008
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In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 26:3, s. 145-151
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Journal article (peer-reviewed)abstract
- In this study, 90W–7Ni–3Fe heavy alloy was investigated for its microstructure development, mechanical properties and fracture behavior after solid state sintering. The nano-sized powders were synthesized by mechanical alloying (MA). The microstructure of solid state sintered heavy alloys consisted of tungsten matrix. The average tungsten grain size in the range of 1.7–3.0 μm was obtained. It was found that the grain size largely affected the mechanical properties. Tensile strength more than 1200 MPa was achieved at a sintering temperature of 1350 °C. Fracture mechanisms based on microscopical observations on the fracture surfaces were studied. Matrix failure, tungsten-intergranular cleavage and tungsten–matrix interfacial separation were found to be the possible failure mechanisms.
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| 7. |
- Akhtar, Farid, et al.
(author)
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Effect of WC particle size on the microstructure, mechanical properties and fracture behavior of WC--(W, Ti, Ta) C--6wt% Co cemented carbides
- 2007
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 25:5-6, s. 405-410
-
Journal article (peer-reviewed)abstract
- This study deals with the microstructure and mechanical properties of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides fabricated by conventional sintering. The conventional WC particles of 4 μm size and ultrafine particles of 0.2 μm were introduced in the system with varying ratio. The ratios of conventional WC particles to ultrafine WC particles were 2:1, 1:1, and 1:2. The microstructures of sintered WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides were sensitively dependent on the ratio of conventional WC particles to ultrafine WC particles. The rim phase increased with the increase in the amount of ultrafine particles. Hardness of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbide increased with increase in the amount of rim phase and decrease in the average grain size of WC particles. The bending strength showed the similar trend of the hardness. The fracture morphologies are reported. The fracture behavior changed from mixed mode to transgranular fracture mode, when the ratio of conventional WC particles to ultrafine WC particles was changed from 2:1 to 1:2.
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| 8. |
- Andersson, KM, et al.
(author)
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Oxidation and dissolution of tungsten carbide powder in water
- 2000
-
In: International journal of refractory metals & hard materials. - 0263-4368. ; 18, s. 35-43
-
Journal article (peer-reviewed)abstract
- The oxidation and dissolution of tungsten carbide powder dispersed in water was investigated using XPS and leaching studies. We found that the WO3 surface layer on the oxidised tungsten carbide powder dissolves readily at pH>3 with the tungsten concentration increasing linearly with time. Adding cobalt powder to the tungsten carbide suspension resulted in a significant reduction of the dissolution rate at pH<10, when the concentration of dissolved Co is high in the solution phase. Electrokinetic studies indicate that the reduced dissolution rate may be related to the formation of surface complexes; experiments showed that Co species in solution adsorb on the oxidised tungsten carbide powder. The experimental data were discussed in relation to theoretical modelling of the WO3 solution chemistry and the Co2+ adsorption at oxide/water interfaces
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| 9. |
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| 10. |
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| 11. |
- Angseryd, Jenny, 1979, et al.
(author)
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Nanostructure of a cubic BN cutting tool material
- 2015
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 49:1, s. 283-287
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Journal article (peer-reviewed)abstract
- Advanced microscopy techniques, laser assisted atom probe tomography and electron energy loss spectroscopy in transmission electron microscopy are used to investigate in detail the microstructure of a polycrystalline cubic boron nitride tool material. During sintering at high pressure superhard cubic boron nitride combines with hard ceramic Ti(C,N) to form a dense material. Diffusion in Ti(C,N) and reactions between Ti(C,N), cBN and additives result in the formation of several nitride, oxide and boride phases in a complex mixed microcrystalline and nano- crystalline microstructure.
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| 12. |
- Bakken, Kristine, 1990, et al.
(author)
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Effect of post-annealing on the thermal stability and residual stresses in CVD (Al,Ti)N coatings investigated by in situ synchrotron diffraction
- 2024
-
In: International Journal of Refractory Metals and Hard Materials. - 0263-4368 .- 2213-3917. ; 124
-
Research review (peer-reviewed)abstract
- The stress in thin wear resistant coatings is of great importance for the performance and service life of tools for metal cutting. In this work we have performed detailed investigations of the phase stability and temperature-dependent residual stresses in Al-rich AlxTi1-xN ((Al,Ti)N) coatings deposited by chemical vapor deposition (CVD) on cemented carbide substrates. One as-deposited (Al,Ti)N coating and one coating post-annealed at 850 °C for 3 h were heated to 1200 °C while the structure and residual stresses were monitored by in situ high energy synchrotron X-ray diffraction. In the as-deposited state, the coating is in tensile stress at room temperature, but post-annealing resulted in a reduction of the room temperature residual stress. This lowering can be explained by growth of hexagonal AlN (hAlN) at the (Al,Ti)N grain boundaries during the isothermal hold time. Upon heating, the temperature-dependence of the residual stresses in both coatings are initially controlled by the mismatch in coefficients of thermal expansion (CTE) with the substrate, which leads to compressive stresses at typical service temperatures. Decomposition starts gradually at around 850–900 °C, resulting in an accelerated development of large compressive stresses with increasing temperatures, until the entire coating is transformed at temperatures just below 1100 °C. The growth of hAlN initiates slightly higher in temperature after post-annealing, whereas the upper limit for complete transformation remains unaffected. The lowered room temperature tensile stress after post-annealing leads to higher compressive stress at service temperatures, which is expected to improve the performance and service time of the coated tool.
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| 13. |
- Beste, Ulrik, et al.
(author)
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Wear induced material modifications of cemented carbide rock drill buttons
- 2006
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In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 24:1-2, s. 168-176
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Journal article (peer-reviewed)abstract
- The drill crown of a rock drill is made of steel and equipped with WC/Co cemented carbide buttons (or inserts) of different geometries. These rock drill button are exposed to a large number of high load impacts into the rock. The complex and strongly shifting properties of rock minerals lead to a complex mixture of wear mechanisms. These wear mechanisms have recently been mapped by the present authors, and are divided into five classes of deterioration and five classes of material removal mechanisms. In this paper, two important deterioration mechanisms are studied in detail, namely the binder phase degradation and the rock intermixing.Transmission electron microscopy (TEM) has been employed for these high resolution studies. However, rock intermixture and huge internal stresses in the buttons lead to severe difficulties in preparing samples.Therefore, a focused ion beam-instrument (FIB) has been used to cut cross-section samples in the outermost surface on rock drill buttons. These have been investigated in the TEM by EDS, EFTEM, and STEM.Buttons from two rock drills of different history were selected for this investigation. One was used to drill 18 m in a hard rock type (quartzitic granite) and the other to drill 20 m in a much softer rock type (magnetite). Only selected regions of the outermost WC grain layers, which are in a steady state wear mode, were investigated.The crystallographic structure of the Co binder phase was investigated in both buttons, and it was represented mainly by the hcp-Co, but also small extent of fcc-Co. This is suggested to be a result of the mechanical fatigue, following one of two suggested Co-phase transformation series.The rock covers and intermixed zones formed were analysed in detail. The large part of the rock cover was found to be amorphous, containing rock and WC fragments. Adjacent to the WC grains, the rock cover was often found to have a porous structure, where the pores were surrounded by crystalline Co-particles adjacent to a carbon rich area. Apparently, the quartz rock locally melts and sticks very intimately to the WC grains and the porous structure forms during solidification. This feature was further analysed, and it was shown that the amorphous rock is seamlessly connected to WC on the atomic level. It was also stated that the rock cover and intermixed layers are very similar on both buttons, independent of rock type drilled.
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| 14. |
- Bonvalet, M., et al.
(author)
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Modelling of prismatic grain growth in cemented carbides
- 2019
-
In: International journal of refractory metals & hard materials. - : ELSEVIER SCI LTD. - 0263-4368. ; 78, s. 310-319
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Journal article (peer-reviewed)abstract
- A mean-field model dealing with prismatic grain growth during liquid phase sintering of cemented carbides with a Co-rich binder is presented. The evolution of the size of an assembly of non-spherical grains is obtained using a Kampmann-Wagner approach and by introducing a constant shape factor between the characteristic lengths of prisms. This factor is a function of interfacial energies of the two kind of facets, basal and prismatic, considered. The growth model is based on three different mechanisms, that can be rate limiting, taking place in series: 2D nucleation of a new atomic layer, mass transfer across the interface and long-range diffusion. The driving force for coarsening is distributed between the different facets. These equations are solved numerically, and the simulation results reveal that the specific abnormal grain growth phenomena experimentally observed in cemented carbides may be reproduced with this new more realistic description of the grain shape contrary to the spherical approach developed in the past. It is also shown that the initial powder size distribution, and more specifically its shape has a strong influence on the distribution of the driving force between the different rate limiting mechanisms and thus on the occurrence of abnormal grain growth. In that case, the self-similarity of the normalized grain size distribution over time is not achieved.
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| 15. |
- Borgh, Ida, et al.
(author)
-
Effect of carbon activity and powder particle size on WC grain coarsening during sintering of cemented carbides
- 2014
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 42, s. 30-35
-
Journal article (peer-reviewed)abstract
- Liquid-phase sintering is an important step in the production of cemented carbides. During sintering, the average WC grain size increases, leading to a coarser structure, which affects the performance of the final product. The coarsening occurs by dissolution of small grains and growth of large grains. In the present work, the effect of high carbon activity during sintering on the WC grain coarsening has been evaluated using electron backscattered diffraction (EBSD) and the results have been compared with a previous work where sintering was performed at a lower carbon activity. A more homogeneous grain size distribution was observed in alloys sintered at a high carbon activity. In addition, the effect of the initial powder particle size distribution was investigated. It was found that the coarsening rate of a WC powder with an initial small average grain size is significantly higher as compared to the coarsening rate for a powder with a larger initial average grain size. The results obtained emphasize the importance of considering the complete particle size distribution in order to predict coarsening.
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| 16. |
- Borgh, Ida, et al.
(author)
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Influence of nitrogen Gas pressure on the miscibility Gap in the Ti-Zr carbonitride system
- 2012
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 32, s. 11-15
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Journal article (peer-reviewed)abstract
- The microstructure of cemented carbides with a gradient structure at the surface consists of WC, cubic carbonitrides and a binder phase. The carbonitrides can, for example, consist of Ti(C,N)-Zr(C,N) where it is reasonable to believe that there is a miscibility gap with Ti-rich and Zr-rich carbonitrides. In the present work, the effect of the N-2-gas pressure on the equilibrium composition of the miscibility gap in the (Ti,Zr)(C,N) system has been investigated. In the study, the carbonitride system is in equilibrium with: WC, liquid binder, graphite and, N-2-gas of different pressures. Both Fe and Co are used as binder phase to study the effect of the binder phase. The results verify that there is a miscibility gap in the carbonitride system and that the region of the miscibility gap will change when N is introduced. There is a critical N-2-gas pressure lower than 0.1 bar and above that pressure the compositions of the carbonitride are rather constant as a result of the formation of a surface rim.
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| 17. |
- Borgh, Ida, et al.
(author)
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Microstructure, grain size distribution and grain shape in WC-Co alloys sintered at different carbon activities
- 2014
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368 .- 0958-0611. ; 43, s. 205-211
-
Journal article (peer-reviewed)abstract
- The properties of cemented carbides strongly depend on the WC grain size and it is thus crucial to control coarsening of WC during processing. The aim of this work was to study the effect of sintering at different carbon activities on the final microstructure, as well as the coarsening behavior of the WC grains, including the size distribution and the shape of WC grains. These aspects were investigated for five WC-Co alloys sintered at 1410 degrees C for 1 h at different carbon activities in the liquid, in the range from the graphite equilibrium (carbon activity of 1) to the eta (M6C) phase equilibrium (carbon activity of 0.33). The grain size distribution was experimentally evaluated for the different alloys using EBSD (electron backscatter diffraction). In addition, the shape of the WC grains was evaluated for the different alloys. It was found that the average WC grain size increased and the grain size distribution became slightly wider with increasing carbon activity. Comparing the two three-phase (WC-Co-eta and WC-Co-graphite) alloys a shape change of the WC grains was observed with larger grains having more planar surfaces and more triangular shape for the WC-Co-graphite alloy. It was indicated that in alloys with a relatively low volume fraction of the binder phase the WC grain shape is significantly affected by impingements. Moreover, after 1 h of sintering the WC grains are at a non-equilibrium state with regards to grain morphology. (C) 2013 Elsevier Ltd. All rights reserved.
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| 18. |
- Bushlya, V., et al.
(author)
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Sintering of binderless cubic boron nitride and its modification by β-Si3N4 additive for hard machining applications
- 2020
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368. ; 86
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Journal article (peer-reviewed)abstract
- This study present the results of HP-HT sintering, microstructure, properties, and performance of binderless cBN tool material. Within the investigated sintering temperature range of 1900–2600 °C the optimum was found to be 2200–2300 °C. Lower temperature results in incomplete diffusion bonding between cBN grains, while higher temperature results in high degree of recrystallization of initial structure, grain growth, and even formation of hexagonal boron nitride in triple joints. Introduction of stress-inducing β-Si3N4 minor inclusions resulted in high overall mechanical and thermal properties: HK = 41 GPa; KIC = 12.6 MPa·m1/2; λ = 180 W/(m·K). Machining experiments in roughing of hardened tool steels show that binderless cBN material provides high performance in terms of resistance to tool cratering, chipping, and tool fracture.
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| 19. |
- Canovic, Sead, 1979, et al.
(author)
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CVD TiC/alumina and TiN/alumina multilayer coatings grown on sapphire single crystals
- 2010
-
In: International Journal of Refractory Metals & Hard Materials. - : Elsevier BV. - 0263-4368. ; 28:2, s. 163-173
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Journal article (peer-reviewed)abstract
- Multilayers of TiC/alpha-Al2O3 and TiN/kappa-Al2O3, consisting of three (1 mm thick) alumina layers separated by thin TiC or TiN (similar to 20 nm thick) layers, have been deposited onto c- and r-surfaces of single crystals of alpha-Al2O3 by chemical vapour deposition (CVD). The aim of this paper is to describe and compare the detailed microstructure of the different multilayer coatings by using transmission electron microscopy (TEM). The general microstructure of the alumina layers is very different when deposited onto different surfaces of alpha-Al2O3 single crystal substrates. On the c-surface the alumina layers grew evenly resulting in growth of single crystal layers of TiC or TiN and alumina throughout the coating. However, when deposited on the r-surface the alumina layers generally grow unevenly. The kappa -> alpha transformation occurs in TiN/kappa-Al2O3 multilayer coatings when deposited on both c- and r-surface substrates. In each layer the transformation starts at the interfacial pores in the upper part and proceeds inwards. The inner layer starts to transform first before the transformation proceeds to the outer layers. The microstructure of the transformed alpha-Al2O3 layers is different compared to as-deposited alpha-Al2O3, e.g. several voids and dislocations are present within the transformed alpha-Al2O3 layers. No pores were observed within the as-deposited alumina layers while a small number of pores was observed at the interfaces below the TiC and TiN layers. However, linkage of pores was observed within the transformed alpha-Al2O3 layers. There are also pores present in the substrate below the innermost TiC and TiN layers. It is believed that they are formed due to chemical etching during the deposition of the TiC and TiN layers. Single crystal TiC/alumina and TiN/alumina layers grow epitaxially on the c-surface substrates with close-packed planes growing on close-packed planes. On the r-surface, epitaxy is present only at some rare locations in alpha(r-sub)-TiC/Al2O3. However, in alpha(r-sub)-TiN/Al2O3 no epitaxy was observed. (C) 2009 Elsevier Ltd. All rights reserved.
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| 20. |
- Chen, Jinhan, et al.
(author)
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The effect of hot isostatic pressing on thermal conductivity of additively manufactured pure tungsten
- 2020
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 87
-
Journal article (peer-reviewed)abstract
- The crack-healing behaviors and microstructure evolution of pure tungsten produced by laser powder bed fusion (LPBF) were studied and compared before and after post hot isostatic pressing (post-HIP) treatment. An average thermal conductivity of 133 W.m(-1).K-1 at room temperature (RT) was obtained after HIP, which was 16% higher than that of as-built sample (115 W.m(-1).K-1). Although the HIP process had little effect on density, it resulted in a large grain size of > 300 mu m accompanied by a decrease in dislocation density and crack healing, which led to a substantial improvement of thermal conductivity of pure tungsten. The positive correlation between relative density and thermal conductivity of as-built tungsten was reported.
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| 21. |
- Ciurans Oset, Marina, 1993-, et al.
(author)
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Use of AFM topography images to determine microindentation hardness of cast tungsten carbide powders
- 2022
-
In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 107
-
Journal article (peer-reviewed)abstract
- Hardness is defined as the resistance of a material to localized plastic deformation. Owing to their non-destructive nature, static indentation hardness tests are widely used in industry. Hardness testing is particularly useful for the mechanical characterization of materials that cannot be tested otherwise, e.g. powdered materials. In this study, challenges related to Vickers microindentation hardness testing of hard brittle cast tungsten carbide (CTC) powders were extensively investigated. Test load was optimized to obtain sufficiently large crack-free indentations allowing for precise measurement of the diagonal lengths. The influence of the operator and imaging technique on the measured hardness value was evaluated. Topography of residual imprints was investigated using atomic force microscopy (AFM) and a systematic and operator bias-free method to locate the indentation vertexes was developed. Results suggested that measurement variability introduced by AFM scanning and post-processing was as low as 3.1% and 1.3% with respect to the mean hardness value, respectively. Since the variability due to the measuring system can be isolated, the homogeneity of powders can be reliably evaluated from the hardness measurements thus obtained.
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| 22. |
- Edin, Emil, et al.
(author)
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MD study of C diffusion in WC/W interfaces observed in cemented carbides
- 2019
-
In: International journal of refractory metals & hard materials. - : ELSEVIER SCI LTD. - 0263-4368. ; 85
-
Journal article (peer-reviewed)abstract
- WC/Co tool used in the turning of Ti-alloys are subject to rapid crater wear due to chemical processes at the tool chip interface in the form of dissolution/diffusion. It has been observed that a thin layer of bcc W forms on the outermost WC grains in contact with the Ti workpiece meaning that C has diffused away from the WC. The rates involved in this process are of interest for formulating a theory of how wear progresses during turning of Ti-alloys. In this work we investigate the rates involved in this diffusion process by means of classical MD simulations on 6 different WC/W interfaces, 3 with a basal WC surface and 3 with a prismatic WC surface, as a function of C depletion in the outermost WC layer. The results show that all interfaces are stable and that principally no diffusion events of C occur at temperatures below 1373 K for C depletion levels below 30 at.%. At 50 at.% depletion, C diffusion starts occurring regularly and at 70 at.% depletion and above the majority of the C atoms are diffusing except at the lowest temperatures. Additionally, any difference in diffusion rate observed between the basal and prismatic interfaces in their pristine states have vanished at the point of 50 at.% depletion. This all points to a process which is initially slow for each layer of the WC but which increases in speed substantially as C atoms are removed.
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| 23. |
- Engqvist, H, et al.
(author)
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A study of grain boundaries in a binderless cemented carbide
- 1998
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In: International journal of refractory metals & hard materials. - : ELSEVIER SCI LTD. - 0263-4368. ; 16:4-6, s. 309-313
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Journal article (other academic/artistic)abstract
- The microstructure of a binderless cemented carbide with <0.5 wt% Co has been analysed using transmission electron microscopy (TEM) in combination with an electron energy loss spectroscopy (EELS) detector and an imaging filter. In particular, microstructu
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| 24. |
- Eriksson, Mirva, et al.
(author)
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Spark plasma sintering of wc, cemented carbide and functional graded materials
- 2013
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 36, s. 31-37
-
Journal article (peer-reviewed)abstract
- Spark plasma sintering (SPS) is an extremely fast solidification technique for compounds that are difficult to sinter within the material group's metals, ceramics, or composites thereof. SPS uses a uniaxial pressure and a very rapid heating cycle to consolidate these materials. The heating is generated by Joule effect when a strong, pulsed electric current passes the conductive graphite die and also through the sample, if conductive. Cemented carbides (hard metals) are mostly used for metal cutting and drilling, wood cutting or rock drilling tools and are consolidated either by pressureless sintering (PLS), hot pressing (HP), or hot isostatic pressing (HIP). With SPS the main benefit is the ability to control the WC grain size due to the short sintering times at high temperature. In addition, unwished reactions between WC and cobalt to form other phases are minimized. By SPS the amount of cobalt can be reduced towards zero in fully dense WC materials. With this technique it is easy to prepare gradient materials where a ductile weldable metal can be joined with the cemented carbide part.
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| 25. |
- Fazakas, E., et al.
(author)
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Experimental and theoretical study of Ti20Zr20Hf20Nb20X20 (X = V or Cr) refractory high-entropy alloys
- 2014
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 47, s. 131-138
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Journal article (peer-reviewed)abstract
- We investigated the microstructure and mechanical properties of Ti20Zr20Hf20Nb20X20 (X = V or Cr) high-entropy alloys (HEA), produced by induction melting and casting in inert atmosphere. The structures of these alloys were studied via X-ray diffractometry and scanning electron microscopy. Results show that Ti20Zr20Hf20Nb20X20 has mainly the body centered cubic (BCC) structure, whereas the BCC matrix of Ti20Zr20Hf20Nb20X20 contains small amount of Cr2Nb and Cr2Hf intermetallic compounds. Ti20Zr20Hf20Nb20X20 alloy shows the high strength and the homogeneous deformation under compression at room temperature. The strength and hardness of Ti20Zr20Hf20Nb20X20 alloy are further enhanced by the Cr-containing Laves phases segregated during casting. The structural and mechanical properties remained almost unchanged after a short time (10 min) heat treatment at 573, 773, 973 and 1173 K indicating the resistance to working temperature peaks for these two alloys. Ab initio calculations predict ductile behavior for these and similar refractory HEM. The theoretically calculated Young's modulus E is in good agreement with the experimental ones.
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| 26. |
- Feng, Peizhong, et al.
(author)
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Mechanically activated reactive synthesis of refractory molybdenum and tungsten silicides
- 2008
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 26:3, s. 173-178
-
Journal article (peer-reviewed)abstract
- In this study, processing of elemental powders mixtures was carried out by mechanical alloying (MA) and heat treatment in vacuum at 700–1000 °C for 1 h. The phase transformation of the powders was investigated by X-ray diffractometer (XRD). The results showed that mechanical alloying promoted the formation of a solid solution of elemental powders. The energy stored in the powders was increased as a result of exterior energy and the barrier energy of the formation of the compound could be exceeded easily. Intermetallics of MoSi2, WSi2, Mo5Si3, Mo3Si and SiC/MoSi2 composite powders were synthesized by mechanically activated reactive synthesis (MARS). The mechanically induced self-sustaining reaction was observed in MoSi2 and MoSi2 + 10 wt%SiC stoichiometry system. It has concluded that mechanically activated reactive synthesis is an effective method for the preparation of high melting-point refractory compounds.
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| 27. |
- Garcia, Jose, et al.
(author)
-
Controlling cobalt capping in sintering process of cermets
- 2017
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 62, s. 126-133
-
Journal article (peer-reviewed)abstract
- Critical sintering parameters for the formation of cobalt capping on cermets were evaluated experimentally. The results were compared to existing theories regarding cobalt capping formation on cemented carbides. Four different cermets grades were selected. The influence of the carbon activity, the sintering atmosphere (vacuum, flow rate, gas mixture, pressure) and the cooling rate was investigated. The results are in accordance with the observations that the Co surface top-layer forms during a specific short temperature interval during the cooling step for each grade, but it is affected by the preceding conditions; e.g. enhanced by a preceding Co-enrichment in the surface zone in a decarburizing atmosphere. The formation can be inhibited by using a carburizing atmosphere, such as carbon monoxide gas, or a sinter-HIP (hot isostatic pressure) step during cooling. A phenomenological model for formation of Co-capping in cermets considering melting point of alloys, cobalt migration, carbon activities, vapor pressure of reactive elements as well as processing parameters (sintering atmosphere, cooling rate etc.) is discussed.
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| 28. |
- Garcia, J., et al.
(author)
-
Kinetics of formation of graded layers on cemented carbides : Experimental investigations and DICTRA simulations
- 2011
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368. ; 29:2, s. 256-259
-
Journal article (peer-reviewed)abstract
- Kinetics of formation of fcc-free layers on Co-W-Ti-Ta-Nb-C-N cemented carbides was investigated by experimental methods and DICTRA simulations. The layer formation obeys a parabolic law, indicating a diffusion-controlled process. For DICTRA simulations, the influence of the mobilities for all diffusing elements in the liquid binder phase at the sintering temperature was investigated. The best agreement between experimental and simulations was obtained considering that the mobility of all metallic elements is two times slower compared with the mobility of the non-metallic elements. © 2010 Elsevier Ltd. All rights reserved.
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| 29. |
- Gren, Martin, 1989, et al.
(author)
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A computational study of the temperature dependence of interface and surface energies in WC–Co cemented carbides
- 2020
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 87
-
Journal article (peer-reviewed)abstract
- Interfaces and surfaces often play a vital role for the properties of polycrystalline materials, such as cemented carbides, and the study of these planar defects is, therefore, of great importance. Cemented carbides (or hardmetals) is a unique class of materials where hard carbide (WC) grains, usually micrometer sized, are embedded in a more ductile metal binder phase (usually Co) in order to combine superb strength with high hardness, making them ideal as tool material in e.g. metal machining. In the manufacturing and industrial usage of cemented carbides temperatures reach high levels, especially in the former case where the material is sintered at temperatures where the binder phase is a liquid. This is a computational study of the temperature dependence of interface and surface energies in WC–Co cemented carbides upto and above the melting temperature of Co. We make use of an analytical bond order potential (ABOP) fitted to density functional theory (DFT) data in order to make the free energy calculations feasible. A variety of free energy methods are used: including quasi harmonic approximation, temperature and thermodynamic integration, and calculation of liquid surface tension and work of adhesion for phase boundaries. We present the temperature dependent interface and surface energies for some typical cases, data which should be useful as a supplement to other studies limited to 0 K.
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| 30. |
- Gruber, Paul H., et al.
(author)
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WC-Ni cemented carbides prepared from Ni nano-dot coated powders
- 2023
-
In: International journal of refractory metals & hard materials. - : Elsevier Ltd. - 0263-4368. ; 117
-
Journal article (peer-reviewed)abstract
- This study presents a novel approach for the synthesis of WC-Ni cemented carbides with enhanced mechanical properties. A low-cost solution-based route was used to coat WC powders with well-distributed metallic nickel dots measuring between 17 nm and 39 nm in diameter. Varying compositions with loadings of 2, 6, and 14 vol% Ni were consolidated using spark plasma sintering (SPS) at 1350 °C under 50 MPa of uniaxial pressure giving relative densities of 99 ± 1 %. The sintered WC-Ni cemented carbides had an even distribution of the Ni binder phase in all compositions, with retained ultrafine WC grain sizes of 0.5 ± 0.1 μm from the starting powder. The enhanced sinterability of the coated powders allowed for consolidation to near theoretical densities, with a binder content as low as 2 vol%. This is attributed to the uniform distribution of nickel and an extensive Ni-WC interface existing prior to sintering. The small size of the Ni dots likely also contributed to the solid-state sintering starting temperatures of as low as 800 °C. The mechanical performance of the resulting cemented carbides was evaluated by measuring the hardness at temperatures between 20 °C and 700 °C and estimating toughness at room temperature using Vickers indentations. These results showed that the mechanical properties of the WC-Ni cemented carbides synthesised by our method were comparable to conventionally prepared WC-Co cemented carbides with similar grain sizes and binder contents and superior to conventionally prepared WC-Ni cemented carbides. In particular, the 2 vol% Ni composition had excellent hardness at room temperature of up to 2210HV10, while still having an indentation fracture toughness of 7 MPa·m0.5. Therefore, WC-Ni cemented carbides processed by this novel approach are a promising alternative to conventional WC-Co cemented carbides for a wide range of applications.
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| 31. |
- Hakeem, Abbas Saeed, et al.
(author)
-
Synthesis and characterization of alkaline earth and rare earth doped sialon Ceramics by spark plasma sintering
- 2021
-
In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 97
-
Journal article (peer-reviewed)abstract
- Several sialon ceramics compositions were synthesized by selecting metal oxides (MOs) in the nanosize range as additives in the oxynitride network. Nanosized precursors, including Si3N4, SiO2, AlN, Al2O3, and MO (MO =MgO, CaO, SrO, BaO, Y2O3, La2O3, CeO2, Nd2O3, Eu2O3, Dy2O3, Er2O3 and Yb2O3,) were used in the present study. Probe sonication and spark plasma sintering techniques were used for mixing the powder precursors and subsequent synthesis of sialon ceramics at a relatively low temperature of 1500 ◦C. Formation of α-sialon(general formula represented by Mm/vSi12-(m+n)Alm+nOnN16-n) was investigated for m and n values of 1.1 and 0.6, respectively and their structural, morphological, thermal, and mechanical properties were evaluated. The synthesized samples were characterized using X-ray diffractometry and field emission scanning electron microscopy to study the effect of the MOs on the microstructure and resulting densification, hardness, fracture toughness, thermal expansion, and thermal conductivity. The sialon samples synthesized using the selected MOs exhibited similar relative densities in the range of 96 to 99% among all the samples and Vickers hardness (HV10) values, in the range of 15 to 20.8 GPa, depending on the type of MO. However, RE MOs exhibited a higher HV than AE MOs.Fracture toughness (KIc) was ~4 MPa⋅m1/2 for most of the samples, but the sample doped with Yb2O3 had the highest KIc of 6.3 MPa⋅m1/2. The thermal conductivity decreased as the atomic number (atomic radii) of the AE increases and in the case of RE exhibited a random tendency. On the other hand, the thermal expansion coefficient increased with increasing atomic radii of the AE, and a mixed trend, with values in the range of 2.63 to2.83 ppm⋅K-1, was observed for RE doped sialon ceramics. These behaviors are attributed to the resulting morphology and structure of alpha sialon comprised of both equiaxed and elongated grains. The properties of these sialon ceramics could be tailored by the proper selection of suitable precursors and synthesis parameters.
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| 32. |
- Hardell, Jens, et al.
(author)
-
Tribological performance of surface engineered tool steel at elevated temperatures
- 2010
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 28:1, s. 106-114
-
Journal article (peer-reviewed)abstract
- Tribological components operating at elevated temperatures can experience high wear, oxidation, thermal fatigue and changes in mechanical properties. In this work, the friction and wear characteristics of plasma nitrided and surface coated (CrN and TiAlN) tool steel during sliding against AISI52100 bearing steel have been studied at room temperature and 400 oC respectively using a ball on disc machine. Surface profiler and SEM/EDS techniques were used to characterise the surface topography and resulting surface damage of the test specimens. The results show that the friction of plasma nitrided tool steel during sliding against bearing steel ball is very high at room temperature and it drastically drops at 400oC. The wear is mainly abrasive at room temperature and adhesive at elevated temperatures. In case of CrN coated tool steel the friction is high but its wear is negligible at room temperature. At 400oC, the friction decreases marginally and transfer of bearing steel to the coated CrN coated disc has been observed. The TiAlN coating has shown relatively lower friction, compared to CrN and negligible wear at room temperature. At 400oC, the friction is very high and unstable and transfer of TiAlN coating to the mating ball occurs.
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| 33. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Heinrichs, Jannica, 1982-, et al.
(author)
-
Initial deformation and wear of cemented carbides in rock drilling as examined by a sliding wear test
- 2017
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 64, s. 7-13
-
Journal article (peer-reviewed)abstract
- Due to a combination of high hardness and toughness, resulting in excellent wear resistance, cemented carbides are commonly used as the rock crushing component in rock drilling. The present paper presents a unique study where the very initial stages of deformation and wear of cemented carbide in sliding contact with rock are followed in small incremental steps. After each step, a pre-determined area within the wear mark is characterized using high resolution SEM and EDS. This facilitates analysis of the gradual deformation, material transfer, degradation and wear. The deterioration mechanisms found in this sliding test are similar to those observed in actual rock drilling. Cemented carbide grades with different microstructures show significant differences, where a higher amount of Co and a larger WC grain size both are associated to more wear.
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| 38. |
- Heinrichs, Jannica, 1982-, et al.
(author)
-
On the deformation mechanisms of cemented carbide in rock drilling : Fundamental studies involving sliding contact against a rock crystal tip
- 2018
-
In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 77, s. 141-151
-
Journal article (peer-reviewed)abstract
- Cemented carbide is a composite material, most commonly consisting of tungsten carbide grains in a metallic matrix of cobalt. The combination of a hard ceramic phase in a ductile metallic matrix combines high hardness and ability to withstand plastic deformation with toughness to avoid cracking and fracturing. Since these properties are very important in rock drilling, cemented carbides are frequently used in such applications. In earlier work, it was found that granite in sliding contact with considerably harder cemented carbides not only results in plastic deformation of the cemented carbide composite, but also in plastic deformation of some of the individual WC grains. The latter observation is remarkable, since even the two hardest granite constituents (quartz and feldspar) are significantly softer than the WC grains. This tendency to plastic deformation of the WC grains was found to increase with increasing WC grain size. The present investigation aims to increase the understanding of plastic deformation of cemented carbides in general, and the individual WC grains in particular, in a situation representative for the rock drilling application. The emphasis is put on explaining the seemingly paradoxical fact that a nominally softer counter material is able to plastically deform a harder constituent in a composite material. The experimental work is based on a scratch test set-up, where a rock crystal tip slides against a fine polished cemented carbide surface under well-controlled contact conditions. The deformation and wear mechanisms of the cemented carbide are evaluated on the sub-micrometer scale; using high resolution FEG-SEM, EDS, EBSD, BIB and FIB cross-sectioning. The size of the Co-pockets, together with the shape and size of WC grains, turned out to be decisive factors in determining the degree of carbide deformation. The results are discussed with respect to their industrial importance, including rock drilling.
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| 39. |
- Hou, Ziyong, et al.
(author)
-
Effect of carbon content on the Curie temperature of WC-NiFe cemented carbides
- 2019
-
In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 78, s. 27-31
-
Journal article (peer-reviewed)abstract
- We have investigated the effect of the carbon content on the Curie temperature of a cemented carbide composite material with a Ni-Fe alloy as the binder phase and WC as the hard phase. In the carbon concentration range from 5.72 to 5.83 wt% carbon, which covers the interval where WC coexists with fcc Ni-Fe without other phases (the ‘carbon window’), the Curie temperature rises from 200 to 527 °C. This result indicates the possibility to use the Curie temperature to determine the carbon balance in the system. With thermodynamic calculations and kinetic simulations we can quantitatively establish the correlation between the carbon and tungsten content of the binder phase and the Curie temperature. This strong compositional effect on the Curie temperature is quantitatively very different from the conventional Co-based cemented carbides, with Curie temperatures of about 950–1050 °C.
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| 40. |
- Humail, Islam S, et al.
(author)
-
Tensile behavior change depending on the varying tungsten content of W--Ni--Fe alloys
- 2007
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 25:5-6, s. 380-385
-
Journal article (peer-reviewed)abstract
- Tungsten heavy alloys (WHAs) are metal–metal composites consisting of nearly pure spherical tungsten particles embedded in a Ni–Fe–W or Ni–Co–W or Ni–Cu–W ductile matrix. In this dual phase alloy, there are several complicated relations between the ductile matrix and hard tungsten particles. The aim of this research was to examine the effect of varying tungsten content on the microstructure and mechanical properties of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity and solid volume fraction) were measured and were found to have a significant effect on the mechanical properties of tungsten-based heavy alloys. The result shows that the binding strength between the W and the matrix phase has a major influence on the ductility of tungsten-based alloys. The larger this binding force is, the better the ductility is.
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| 41. |
- Irshad, Hafiz Musammil, et al.
(author)
-
Effect of Ni content and Al2O3 particle size on the thermal and mechanical properties of Al2O3/Ni composites prepared by spark plasma sintering
- 2018
-
In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 76, s. 25-32
-
Journal article (peer-reviewed)abstract
- Alumina-nickel composites were prepared by carrying out spark plasma sintering (SPS) of nano-sized and micro-sized Al2O3particles with 15–45 wt% Ni powders. The powder materials were sintered at a temperature of1400 °C under a constant uniaxial pressure of 50 MPa. FESEM micrographs of the products showed uniformlydispersed nickel inclusions in both matrices at intergranular positions. Presence of Al2O3as the major phasealong with Ni as the minor phase was confirmed using XRD analysis. Thermal and mechanical properties of thenano- and micro-sized Al2O3/Ni composites were investigated. The thermal conductivity of nano-sized aluminacomposites was seen to increase with the increase in nickel content, however, an opposite trend was observed formicro-sized alumina-based composites. Moreover, thermal conductivities of all the composites decreased withincrease in temperature. The composites also showed high hardness and fracture toughness values of up to19.6 GPa and 4.71 MPa ∗ m1/2, respectively, and relative density values, between 79 and 99%, that decreasedwith increasing Ni content. Furthermore, the nano-sized Al2O3/Ni composites showed thermal and mechanicalproperties superior to those of the micro-sized Al2O3/Ni composite.
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| 42. |
- Jakob, Severin, 1991, et al.
(author)
-
Effect of boron doping on grain boundary cohesion in technically pure molybdenum investigated via meso-scale three-point-bending tests
- 2023
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 113
-
Journal article (peer-reviewed)abstract
- Molybdenum has numerous advantageous functional and high-temperature properties. However, plastic deformation as well as structural applications are limited due to a propensity for brittle, intercrystalline failure, especially at low temperatures. It is well known that oxygen segregations have a detrimental effect, whereas it is assessed that carbon and/or boron have a beneficial effect on grain boundary cohesion. An advanced approach for the improvement of these interfaces is segregation engineering, e.g. the addition of cohesion enhancing elements segregating to the grain boundaries. To investigate early stages of crack formation, three-point bending tests on recrystallized commercially pure and boron micro-doped molybdenum were conducted between −28 °C and room temperature. The tensile-loaded top surface of the specimens was examined post-mortem close to the final fracture area via scanning electron microscopy. The occurring separations of grains are investigated for distinct features and the chemical composition of the interface is complementary measured by atom probe tomography.
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| 43. |
- Jakob, Severin, 1991, et al.
(author)
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Evolution of nano-pores during annealing of technically pure molybdenum sheet produced from different sintered formats
- 2023
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 110
-
Journal article (peer-reviewed)abstract
- Molybdenum is a refractory metal with no phase transformation in the solid state and a high melting point. It is therefore an excellent structural material for various high temperature applications. Especially in this field of operation, significant creep resistance is essential. To achieve this, a microstructure with grains in the range of millimeters is desired. However, as demonstrated in the present study, the onset temperature for secondary recrystallization, which would lead to a beneficial grain size, is among other things dependent on the initial dimensions of the sintered part. One possible reason for the different microstructural evolutions is the influence of residual pores in sub-micrometer size. Sheets were thus fabricated via three different production routes employing the same initial Mo powder to exclude chemical variation as an influencing factor. The samples were investigated by in-situ small-angle X-ray scattering at a synchrotron radiation source with two different heating rates. Additionally, selected annealed samples were studied ex-situ with high energy X-rays. The apparent volume fraction of pores is compared to a volatilization model for the vaporization of typical accompanying elements and the induced thermal expansion.
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| 44. |
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| 45. |
- Jayamani, Jayaraj, et al.
(author)
-
Electrochemical and passivation behavior of a corrosion-resistant WC-Ni (W) cemented carbide in synthetic mine water
- 2023
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 114
-
Journal article (peer-reviewed)abstract
- Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9-1.1 mu m). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni-and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.
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| 46. |
- Johansson, Sven A.E., et al.
(author)
-
CCBuilder: a software that produces synthetic microstructures of WC-Co cemented carbides
- 2019
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 78, s. 210-218
-
Journal article (peer-reviewed)abstract
- In this paper, the software CCBuilder and its methods to generate synthetic three-dimensional (3D) microstructures of WC-Co cemented carbides are presented. Generating synthetic microstructures is critical, as it enables accurate virtual testing where influences from microstructural parameters can be investigated in a systematic and controlled way. The model of the microstructure is based on a voxel description of the material volume and the WC grains are represented as truncated triangular prisms. The grains are inserted into the simulation domain and to obtain a realistic microstructure a combination of packing and a Monte Carlo Potts simulation is used. The orientations of all individual WC grains are known and it is shown that the microstructure is built up of two interpenetrating networks, the WC grains and the Co phase. Numerical studies are presented to show how input parameters to CCBuilder, such as grain size, grain shape, packing strategy, voxel density, system size, and Monte-Carlo steps affect the resulting simulated microstructure. The obtained microstructures are geometrically realistic and the contiguity of the carbide phase shows very good agreement with published experimental data.
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| 47. |
- Jones, H. G., et al.
(author)
-
Examination of wear damage to rock-mining hardmetal drill bits
- 2017
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 66, s. 1-10
-
Journal article (peer-reviewed)abstract
- WC/Co mining bits from a drill head used for drilling holes for roof support bolts in a mine were examined using a focused ion beam scanning electron microscope (FIB-SEM). This was combined with energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analyses to study the chemical interaction between the drill bit and the rock. It was found that at the surface of the buttons there was depletion of cobalt, change in chemistry of the remaining binder regions, and changes to the morphology of the WC grains. Tribochemistry calculations were done to understand the possible formation of silicides at the surface of the drill bits, and thus emphasise the importance of quartz content in rock on wear. The evidence of mechanical damage combined with chemical reactions is another step towards understanding the complete wear process in hardmetal mining tools.
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| 48. |
- Kaplan, B., et al.
(author)
-
Study of tool wear and chemical interaction during machining of Ti6Al4V
- 2018
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 72, s. 253-256
-
Journal article (peer-reviewed)abstract
- The present study concerns an investigation of the wear on three uncoated cemented carbide grades, with differing binder content and grain size, during longitudinal turning of Ti6Al4V as a function of cutting speed. The creater wear at end of tool life is studied in detail using electron microscopy and X-ray diffraction. It is observed that decreasing binder content results in slower wear progression and longer tool life. The microstructure of the adhered layer is also dependent on the binder content, where a lower amount of binder results in an increase of dark precipitates in the adhered layer. X-ray diffraction confirms the presence of bcc-W as a chemical wear product at the interface. Diffraction peaks corresponding to cubic (Ti,V)C are also occasionally observed.
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| 49. |
- Kaplan, Bartek, et al.
(author)
-
Thermodynamic calculations and experimental verification in the WC-Co-Cr cemented carbide system
- 2015
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 48, s. 257-262
-
Journal article (peer-reviewed)abstract
- Tungsten carbide and cobalt have always been, and still are, the foundation of cemented carbides. Modem grades include several other alloying elements, apart from just WC-Co, added for several different purposes. For example, by adding chromium it is possible to produce extremely fine grained grades compared to straight WC-Co grades and thus the freedom to tailor the properties of the material is increased. By applying thermodynamic calculations it is possible to design the material and also avoid some of the costly trial-and-error procedures. However, there is also a need for experimental verification in order to have confidence in the predictive calculations. The present work concerns the application of thermodynamic calculations to some relevant compositions together with experimental verification in the WC-Co-Cr system. Special focus is given to the limiting conditions for precipitation of unwanted phases with regards to the Cr-content in the binder, C-content and melting temperatures. No regard is taken to the presumable Cr-solubility in the WC phase itself. (C) 2014 Elsevier Ltd. All rights reserved.
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| 50. |
- Kaplan, Bartek, et al.
(author)
-
Thermodynamic calculations and experimental verification in the WC-Co-Cr cemented carbide system (Reprint of Int. Journal of Refractory Metals and Hard Materials vol 48, pg 257-262, 2015)
- 2015
-
In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 49, s. 400-405
-
Journal article (peer-reviewed)abstract
- Tungsten carbide and cobalt have always been, and still are, the foundation of cemented carbides. Modem grades include several other alloying elements, apart from just WC-Co, added for several different purposes. For example, by adding chromium it is possible to produce extremely fine grained grades compared to straight WC-Co grades and thus the freedom to tailor the properties of the material is increased. By applying thermodynamic calculations it is possible to design the material and also avoid some of the costly trial-and-error procedures. However, there is also a need for experimental verification in order to have confidence in the predictive calculations. The present work concerns the application of thermodynamic calculations to some relevant compositions together with experimental verification in the WC-Co-Cr system. Special focus is given to the limiting conditions for precipitation of unwanted phases with regards to the Cr-content in the binder, C-content and melting temperatures. No regard is taken to the presumable Cr-solubility in the WC phase itself.
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