| 1. |
- Dimitrios, Nikas, et al.
(författare)
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Effect of annealing on microstructure in railway wheel steel
- 2022
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Ingår i: 42Nd Riso International Symposium On Materials Science. - : Institute of Physics Publishing (IOPP). ; 1249
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Konferensbidrag (refereegranskat)abstract
- Railway wheels are commonly made from medium carbon steels (similar to 0.55 wt.% C), heat treated to a near pearlitic microstructure with 5-10% pro-eutectoid ferrite. During the operation of freight trains, where block brakes are used, high thermal loads occur together with the high contact stresses, which combined can affect the mechanical properties of the material. In this study, the effects of annealing on local microstructure and mechanical properties in pearlitic railway wheel steel were investigated using electron microscopy and micro-hardness. It is found that after annealing at 650 degrees C, the room temperature hardness reduces about 25%, accompanied by significant spheroidization of cementite in the pearlitic colonies, though the size and the orientation gradients of the pearlitic colonies have not changed much. The relationship between the microstructural changes and the mechanical properties are discussed.
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| 2. |
- Hosseini, Seyedehsan, 1994
(författare)
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Additive-Driven Improvements in Interfacial Properties and Processing of TMP-Polymer Composites
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efforts to address environmental concerns have resulted in new regulations designed to plan the reduction of plastic and synthetic polymer usage, necessitating the search for sustainable natural alternatives with comparable cost-effectiveness and mechanical performance. Thermomechanical pulp (TMP) fibres are one of the most affordable natural fibres that have no chemical refining in production, production have a high yield of 90-98% and TMP fibres have been demonstrated to improve the mechanical characteristics (strength, stiffness and toughness) of wood-polymer composites (WPCs) compared to the pure polymer. The integration of TMP fibres with non-polar synthetic polymers remains a challenge due to surface polarity differences. This PhD thesis aims to ease the processing of TMP fibre composites through the incorporation of additives. The hypothesis posits that incorporating magnesium stearate (MgSt), molybdenum disulfide (MoS2) and alkyl ketene dimer (AKD) as additives in TMP composites will enhance interfacial properties, resulting in improved processability and flow behaviour at high temperatures. MoS2 is known for its interaction with lignin, which exists in TMP and MgSt is recognised for its ability to improve flow in pharmaceutical processing when combined with cellulose, also a component of TMP. AKD modifies the hydrophilic properties of lignocellulosic surfaces. The experimental work explores the effect of these additives on the properties of TMP composites of ethylene acrylic acid copolymer (EAA) and polypropylene (PP) matrices. The dynamic mechanical analysis (DMA) and mechanical analysis results reveal that MoS2 exhibits superior interaction with TMP fibres, yielding enhanced interfacial properties compared to MgSt in between EAA and TMP fibres. Rheological studies elucidate the transition from a fluid-like state to a network-like structure upon the incorporation of TMP into the PP matrix. The incorporation of AKD with C18 reduces the viscosity of TMP-PP composites and PP itself, and, as determined through theoretical Hansen solubility parameter (HSP) calculations, increases compatibility between cellulose in TMP fibres and PP. The addition of AKD influences both the colour (lighter) and shape (smoother surface) of the extrudate filaments in the TMP-PP composites, indicative of improved processing. In addition, frictional analysis demonstrates the reduction of the coefficient of friction (COF) between metal and TMP fibre by MgSt and AKD treatments.
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| 3. |
- Guldris Leon, Lorena, 1983, et al.
(författare)
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Understanding Mineral Liberation during Crushing Using Grade-by-Size Analysis - A Case Study of the Penuota Sn-Ta Mineralization, Spain
- 2020
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Ingår i: Minerals. - : MDPI AG. - 2075-163X. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- Coarse comminution test-work and modeling are powerful tools in the design and optimization of mineral processing plants and provide information on energy consumption. Additional information on mineral liberation characteristics can be used for assessing the potential of pre-concentration stages or screens in the plant design. In ores of high-value metals (e.g., Ta, W), standard techniques-such as the mineralogical quantification of grain mounts by quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) or chemical analysis by X-ray fluorescence (XRF) can be challenging, due to the low relative abundance of such valuable minerals. The cost of QEMSCAN is also a limiting factor, especially considering the large number of samples required for the optimization of coarse comminution. In this study, we present an extended analytical protocol to a well-established mechanical test of interparticle breakage to improve the assessment of coarse mineral liberation characteristics. The liberation of ore minerals is a function of the rock texture and the difference in size and mechanical properties of the valuable minerals relative to gangue minerals and they may fraction in certain grain sizes if they behave differently during comminution. By analyzing the bulk-chemistry of the different grain size fractions produced after compressional testing, and by generating element by size diagrams, it is possible to understand the liberation characteristics of an ore. We show, based on a case study performed on a tantalum ore deposit, that element distribution can be used to study the influence of mechanical parameters on mineral liberation. This information can direct further mineralogical investigation and test work.
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| 4. |
- Koptyug, Andrey, 1956-, et al.
(författare)
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Electron Beam Melting: from Shape Freedom to Materials Properties Control at Macro- and Microscale
- 2021
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Ingår i: Proceedings of the THERMEC 2020, Graz, Austria. - : Trans Tech Publications. ; , s. 755-759
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Konferensbidrag (refereegranskat)abstract
- Electron beam melting (EBM) is one of the constantly developing powder bed fusion (PBF) additive manufacturing technologies (AM) offering advanced control over the manufacturing process. Freedom of component shapes is one of the AM competitive advantages already used at industrial and semi- industrial scale. Development of the additive manufacturing today is targeting both widening of the available materials classes, and introducing new enabling modalities. Present research is related to the new possibilities in tailoring different material properties within additively manufactured components effectively adding “fourth dimension to the 3D-printing”. Specific examples are given in relation to the electron beam melting, but majority of the conclusions are valid for the laser-based PBF techniques as well. Through manipulating beam energy deposition it is possible to tailor quite different material properties selectively within each manufactured component, including effective material density as well as thermal, mechanical, electrical and acoustic properties. It is also possible to acquire by choice both metal-metal composite and completely alloyed material, when blends of precursor powder are used together with the beam energy manipulation.
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| 5. |
- Shaikh, Abdul Shaafi, 1989, et al.
(författare)
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On the effect of building platform material on laser-powder bed fusion of a Ni-base superalloy HAYNES® 282®
- 2023
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Ingår i: European Journal of Materials. - : Informa UK Limited. - 2688-9277. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) by laser powder bed fusion (LPBF) involves melting of layers of powder onto a substrate, called a building platform. Due to cost or convenience considerations, building platform materials rarely match the LPBF material, especially for high temperature materials. To ensure tolerances in component geometries, AM components are often stress-relieved/heat-treated while still attached to the building platform. It is therefore important to understand the effect of dissimilar building platform materials on the properties of the built-up material. These effects may be particularly important for high performance materials such as Ni-base superalloys used for critical applications in the aerospace and energy industries. To investigate this effect, samples of a Ni-base superalloy HAYNES® 282® were built onto a carbon steel building platform in several configurations. The samples were removed from the building platform after heat treatment and subjected to detailed composition analysis and microstructural characterization to investigate the effect of the building platform material on the properties of the additively manufactured part. Room temperature and high temperature tensile testing were used to characterize the material. Results showed no risk of large-scale chemical composition change, or mechanical property degradation of built-up material from on-platform heat treatment.
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| 6. |
- Vilardell, A. M., et al.
(författare)
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B2-structured Fe3Al alloy manufactured by laser powder bed fusion : Processing, microstructure and mechanical performance
- 2023
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Ingår i: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- Prealloyed Fe3Al was successfully manufactured by laser powder bed fusion. The best set of process parameters led to parts with a relative density of 99.5 %, a surface roughness, Sa, of 31.5 ± 5.6 μm and a hardness of 319 ± 14 HV0.1. Its microstructure as well as its mechanical properties at room and high temperatures were analyzed. The results of the chemical composition showed minor variations in aluminum content oscillating between 21 and 28 at.% along the melt pool. Additionally, elongated grains were observed to grow parallel to the building direction, as well as the development of a weak 001 texture along the building direction. The mechanical properties were influenced by the temperature. Compression tests showed a loss in strength with the increase in temperature, from a yield strength of 621 ± 40 MPa at room temperature to 89 ± 20 MPa at 650 °C. Reciprocating sliding wear tests showed that fragmentation of the intermetallic at room temperature occurs, whereas plastic deformation dominated at higher temperatures. For all temperatures, tribochemical wear was also present due to the oxidation of wear debris.
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| 7. |
- Zhang, Yubin, et al.
(författare)
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Stress relief during annealing of railway wheel steel characterized by synchrotron X-ray micro-diffraction
- 2022
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Ingår i: 42nd Risø International Symposium on Materials Science. - : Institute of Physics Publishing (IOPP). ; 1249
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Konferensbidrag (refereegranskat)abstract
- Railway wheels in service experience rolling contact fatigue loading, but also need to resist frictional heating on braking, yielding temperatures up to 500 degrees C. The combination of mechanical and thermal loads leads to changes in the mechanical properties of the material. The focus of this study is to investigate the effect of annealing on local microstructure and residual stresses in railway wheel pearlitic steel (medium carbon steels, similar to 0.55 wt.% C) using synchroton X-ray Laue micro-diffraction. It is found that the local residual stress releases to a large extent after annealing at 500 degrees C. The stress formation and relief mechanisms and their relationship to the local microstructure are discussed.
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| 8. |
- Edin, Emil, et al.
(författare)
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Rapid method for comparative studies on stress relief heat treatment of additively manufactured 316L
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 847
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Tidskriftsartikel (refereegranskat)abstract
- The additive manufacturing method laser powder bed fusion (L-PBF) is known to introduce large residual stresses in the built component. Optimization of process parameters and subsequent heat treatment is crucial to relieve these residual stresses. However, many of the available tools used to analyze these residual stresses are either prohibitively expensive, or too time consuming for initial prototyping stages.A qualitative method for rapid evaluation of the effectiveness of stress relief heat treatment of L-PBF manufactured 316L has been tested. Residual stress induced distortion has been measured with contact and non-contact methods to study the effect of different stress relief heat treatment temperatures (600 – 950 °C, fixed holding time: 1 h). Over the examined temperature interval, at which deformation was measured, distinct differences were observable at each temperature with both methods. Based on the distortion, shape stability was considered reached after subjecting the test geometry to a heat treatment temperature of 900 °C for 1 hour. Complementary mechanical testing and microstructural characterization were carried out to provide a more general understanding of the implications of each heat treatment temperature. Microstructural characterization revealed that complete dissolution of the cellular sub-grain features occurred at the same temperature as where the minimum magnitude of distortion was obtained.
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| 9. |
- Andersson, Anton, et al.
(författare)
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Ground granulated iron silicate slag as supplementary cementitious material: Effect of prolonged grinding and granulation temperature
- 2023
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Ingår i: Cleaner Materials. - : Elsevier. - 2772-3976. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- The metallurgical and cement industries contribute significantly to anthropogenic carbon dioxide emissions. Utilizing oxidic by-products from the metallurgical industry as supplementary cementitious materials (SCMs) can improve resource efficiency and reduce emissions from cement production. Iron silicate copper slags have been studied as SCMs, but mainly in systems where Portland cement is used as an activator. There is limited research on the inherent reactivity of the slag under changing processing conditions. The present study offers insight into the effect of granulation temperature and grinding on the inherent reactivity of an industrially produced iron silicate copper slag. The results showed that granulation temperature had an insignificant effect on reactivity, while grinding generated substantial improvements. The latter effect was concluded to stem from the increased specific surface area, increased number of sites for nucleation and growth of hydrates, and changes in the inherent reactivity owing to structural changes induced by the grinding.
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| 10. |
- Krakhmalev, Pavel, 1973-, et al.
(författare)
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Influence of heat treatment under hot isostatic pressing (HIP) on microstructure of intermetallic-reinforced tool steel manufactured by laser powder bed fusion
- 2020
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 772
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure and properties of as-built laser powder bed fusion (LPBF) steels differ from the conventional ones, and they may contain some porosity and lack of fusion. Therefore, post-treatments, including hot isostatic pressing (HIP), are used to density the material, and tailor the properties of the final product. Usually, HIP is performed as an operation separate from heat treatment. In the present investigation a new approach was used, in which the whole cycle of the heat treatment was carried out in HIP under pressure, and the influence of HIP on microstructure of an advanced stainless maraging tool steel manufactured by LPBF was investigated. For a comparison, a conventional steel grade of the same chemical composition, after a heat treatment at the same temperature-time conditions, was also characterized. The microstructure of the steel was investigated by means of advanced microscopy and atom probe tomography. The influence of the manufacturing route, heat treatment and HIP on microstructure, austenitic phase fraction and size distribution of precipitates was investigated, and the role of high pressure in stabilization of austenite in the microstructure was discussed. It was concluded that since HIP influences phase transformations, a fundamental understanding of the influence of HIP on microstructure is nececcary, and development of new post processing regimes guaranteeing the best performance of the material is required.
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