| 1. |
- Gåård, Anders, 1977-, et al.
(author)
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Nano-scale friction of multi-phase powder metallurgy tool steels
- 2015
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In: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 1119, s. 70-74
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Journal article (peer-reviewed)abstract
- Friction is a fundamental phenomenon in tribology involving complex mechanisms between thecontacting surfaces. Measurements of friction are often made using devices with substantially largercontact area than dimensions corresponding to microstructural features of the materials. Hence, for multi-phase materials,influence of particular microstructural constituents is not resolved. In the present work, a tribometerwith a contact area in the nano-scale range was used to map friction for different types of tool steelswith different chemical- and phase composition. Owing to the small tip radius, frictionalcharacteristics of primary carbides and the steel matrix were measured and compared. Dependingon chemical composition, a difference was observed where the coefficient of friction wasapproximately twice higher for the steel possessing highest coefficient of friction, including bothcarbides and the steel matrix.
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| 2. |
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| 3. |
- Karlsson, Patrik, 1973-, et al.
(author)
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Galling resistance and wear mechanisms for cold-work tool steels in lubricated sliding against high strength stainless steel sheets
- 2012
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In: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 286-287, s. 92-97
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Journal article (peer-reviewed)abstract
- Tool damage in sheet metal forming of stainless steel is of high concern for the forming industry. In the present work, ingot cast AISI D2 and advanced powder metallurgy tool steel (PM) cold-work tool steels were evaluated and ranked regarding wear mechanisms and galling resistance. Wear tests were performed using a slider-on-flat-surface (SOFS) tribometer in sliding against austenitic–ferritic (duplex) stainless steel sheets at different contact pressures in lubricated conditions. The best galling resistance was observed for the nitrogen alloyed PM tool steels. Abrasive scratching of the tool surfaces and transfer of sheet material due to adhesive wear were the main metal forming tool surface damage mechanisms. By increasing the hardness of one PM sheet metal forming tool grade, the galling resistance was enhanced.
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| 4. |
- Karlsson, Patrik, 1973-, et al.
(author)
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Influence of size and distribution of hard phases in tool steels on the early stage of galling
- 2012
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In: TOOL 2012. - Knittelfeld : Verlag "Gutenberghaus". - 9783901384523
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Conference paper (peer-reviewed)abstract
- In sheet metal forming processes, contact pressures are relatively high and total sliding distances are long, which demands tool steels to prevent tool damage and to resist galling. Galling is related to microscopic and macroscopic material transfer, but, the mechanisms of initiation are not thoroughly understood.To investigate galling initiation, lubricated sliding testing in the Slider-On-Flat-Surface (SOFS) tribometer was performed for ingot cast (IC) AISI D2 type and nitrogen alloyed powder metallurgy (PM) tool steel. The sheet grade was EN 1.4509 ferritic stainless steel. To reveal mechanisms in the early stages of galling initiation, transfer and accumulation of sheet material to the tool surfaces were characterized using AFM and SEM.It was found that already after a short sliding distance, transfer of sheet material occurred covering both the matrix and the hard phases. Macroscopic analysis of the contact area showed that initial material transfer and further lump growth occurred at positions corresponding to high plastic strains in the sheet material. Even though initial material transfer was observed for both tested tool steels, the sliding distance to the point where transfer and further lump formation occurred was longer for the PM tool steel. This was discussed in correlation to differences in size and distribution of the hard phases in the tool steels, which was confirmed by AFM and SEM.
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| 5. |
- Karlsson, Patrik, 1973-, et al.
(author)
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Influence of work material proof stress and tool steel microstructure on galling initiation and critical contact pressure
- 2013
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In: Tribology International. - Amsterdam : Elsevier. - 0301-679X .- 1879-2464. ; 60, s. 104-110
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Journal article (peer-reviewed)abstract
- EN 1.4301 (austenitic), EN 1.4509 (ferritic), EN 1.4162 (duplex) and EN 1.4310 C1000 (metastable austenitic) stainless steels were tested in lubricated sliding against an ingot cast EN X153WCrMoV12 and powder metallurgy nitrogen alloyed Uddeholm Vancron 40 tool steels to reveal critical to galling contact pressure, Pcr. The calculated Pcr were higher for steels with higher strength. At P>Pcr, due to plastic flow of sheet material, the tool is damaged substantially and wear-induced matrix damage causes rapid galling initiation. At P
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| 6. |
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| 7. |
- AlMotasem, Ahmed Tamer, et al.
(author)
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Adhesion between ferrite iron-€“iron/cementite countersurfaces : A molecular dynamics study
- 2016
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In: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 103, s. 113-120
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Journal article (peer-reviewed)abstract
- The adhesive properties of Fe(110)/Fe(110) and Fe3C(001)/Fe(110) countersurfaces have been investigated by using classical molecular dynamics simulations. The simulation results show that Fe3C/Fe exhibits a relatively lower adhesion compared to the Fe/Fe. Additionally, the temperature dependence of the adhesive properties between 300–700 K has been examined. The results demonstrate that, with increasing the temperature, the values of the adhesion force and the work of adhesion continuously decrease in the case of Fe3C/Fe; they initially slightly increase up to 500 K then decrease in the case of Fe/Fe. Furthermore, the effect of lattice coherency between Fe/Fe has been examined and found to slightly reduce the adhesion. These results explain how carbides improve galling resistance of tool steel observed during dry sliding.
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| 8. |
- AlMotasem, Ahmed Tamer, et al.
(author)
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Atomistic insights on the wear/friction behavior of nanocrystalline ferrite during nanoscratching as revealed by molecular dynamics
- 2017
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In: Tribology letters. - New York : Springer. - 1023-8883 .- 1573-2711. ; 65:3, s. 101-
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Journal article (peer-reviewed)abstract
- Using embedded atom method potential, extensive large-scale molecular dynamics (MD) simulations of nanoindentation/nanoscratching of nanocrystalline (nc) iron have been carried out to explore grain size dependence of wear response. MD results show no clear dependence of the frictional and normal forces on the grain size, and the single-crystal (sc) iron has higher frictional and normal force compared to nc-samples. For all samples, the dislocation- mediated mechanism is the primary cause of plastic deformation in both nanoindentation/nanoscratch. However, secondary cooperative mechanisms are varied significantly according to grain size. Pileup formation was observed in the front of and sideways of the tool, and they exhibit strong dependence on grain orientation rather than grain size. Tip size has significant impact on nanoscratch characteristics; both frictional and normal forces monotonically increase as tip radii increase, while the friction coefficient value drops by about 38%. Additionally, the increase in scratch depth leads to an increase in frictional and normal forces as well as friction coefficient. To elucidate the relevance of indentation/scratch results with mechanical properties, uniaxial tensile test was performed for nc-samples, and the result indicates the existence of both the regular and inverse Hall-Petch relations at critical grain size of 110.9 angstrom. The present results suggest that indentation/scratch hardness has no apparent correlation with the mechanical properties of the substrate, whereas the plastic deformation has.
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| 9. |
- AlMotasem, Ahmed Tamer, et al.
(author)
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Tool microstructure impact on the wear behavior of ferrite iron during nanoscratching : An atomic level simulation
- 2017
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In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 370-371, s. 39-45
-
Journal article (peer-reviewed)abstract
- In the present work, molecular dynamics simulations were used to investigate the impact of the tool microstructure on the wear behavior of ferrite workpiece during nanoscratching. The tool microstructure was modified by varying the carbide (cementite) contents. The simulation results show that dislocations are the primary mechanism for plastic deformation of the workpiece material. It is found that total dislocation length varies significantly depending on the carbide content in the tool. Furthermore, other tribological phenomena were also observed to depend on the carbide contents. For example, the average value of frictional forces decreased while the normal force increases with increasing carbide contents, and hence the friction coefficient was decreased. Additionally, the shape and size of lateral and frontal pileups are lowered. The structural analysis of the pileup region reveals the loss of long range order and start of amorphisation. The temperature distribution of the pileup regions showed an increase of the pileup temperature when carbide is added into tool. The wear volume is considerably reduced when the carbide content increases. The average scratch hardness was found to decrease and the result was analyzed with the theoretical Taylor hardening model.
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| 10. |
- Bartels, Dominic, et al.
(author)
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Development of a novel wear-resistant WC-reinforced coating based on the case-hardening steel Bainidur AM for the substitution of carburizing heat treatments
- 2023
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In: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854 .- 2214-0697. ; 26, s. 186-198
-
Journal article (peer-reviewed)abstract
- Laser-based directed energy deposition of metals (DED-LB/M) supports the synthesis of functional materials with tailored properties and performance through in-situ modification of the alloying composition within the processing zone. In this investigation, a low-alloyed steel was modified stepwise to analyse the influence of carbon and tungsten carbide (WC) addition on the resulting material properties. A moderate carbon concentration of 0.4 wt.-% improved the average hardness (520 HV0.5). WC particles on the other hand were dissolved within the matrix and resulted in a fine microstructure with high hardness (780 HV0.5). A combined addition of carbon and WC led to the highest material hardness (840 HV0.5). Scratch tests showed that the wear resistance rises with increasing hardness but is improved the most by the addition of hard particles. Furthermore, these tests revealed an anisotropic abrasive wear resistance which correlates with the direction of the weld tracks. Loading the material parallel to the weld track direction led to a homogeneous wear. When the material is scratched perpendicularly to the weld tracks, an inhomogeneous wear with periodic characteristics occurred. The periodicity can be explained by the different microstructural characteristics and hardness at the transition zone between adjacent weld tracks deposited in DED-LB/M. For all materials, the transition between two weld tracks was characterized by a columnar microstructure with low microhardness while the adjacent weld tracks possessed a finer microstructure and higher microhardness. These microstructural differences were mirrored in scratch testing since wear peaks can be observed at the transition zone between two weld tracks.
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| 11. |
- Bergström, Jens, 1954-, et al.
(author)
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Galling in sheet metal forming
- 2008
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In: Proceedings of the IDDRG 2008 Conference. - Olofström : Industriellt utvecklingscentrum i Olofström AB. - 9789163329487
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Conference paper (other academic/artistic)
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| 12. |
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| 13. |
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Gåård, Anders, 1977-, et al.
(author)
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Wear mechanisms in galling : cold work tool materials sliding against high-strength carbon steel sheets
- 2009
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In: Tribology letters. - : Springer. - 1023-8883 .- 1573-2711. ; 33:1, s. 45-53
-
Journal article (other academic/artistic)abstract
- Transfer and accumulation of adhered sheet material, generally referred to as galling, is the major cause for tool failure in sheet metal forming. In this study, the galling resistances of several tool steels were evaluated against dual-phase high-strength carbon steel using a SOFS tribometer, in which disc-shaped tools were slid against a real sheet surface in dry sliding test conditions. Three different frictional regimes were identified and characterized during sliding, and any transition in friction corresponded to a transition in wear mechanisms of the sheets. The performance of the tools depended on load, material and the particular frictional regime. Best overall performance was obtained by nitrogen-alloyed powder metallurgy tool steel.
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| 21. |
- Hanson, Magnus, et al.
(author)
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Comparison of two test methods for evaluation of forming tool materials
- 2007
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In: Tribotest. - : Wiley. - 1354-4063 .- 1557-685X. ; 14:3, s. 147-158
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Journal article (peer-reviewed)abstract
- Two test methods often used to simulate the tribological performance of forming tool materials are compared in this investigation through an evaluation of the friction and wear properties of four tool steels in dry sliding. One test (slider-on-flat-surface (SOFS)) utilises a vertical disc sliding on a horizontal flat test surface, and the other (load scanner (LS) tests) utilises two crossed cylindrical rods. The test conditions were selected as equal as possible for the two tests, and the following conclusions are made.Somewhat unexpectedly, the friction and wear results differed substantially between the two tests. The SOFS test showed a better potential to evaluate wear resistance since one test sample is in continuous contact with the other. The LS test can generate higher contact pressures since the two rods contact each other in an unworn condition throughout the whole test stroke.LS indicate that two hard and smooth tool steels tested against each other generally give low friction and good galling resistance. The two hard couples tested sustained the highest loads without any detectable surface damage. For the same combinations of hard steels, SOFS gave a higher friction due to the wear of the disc. The carbides in the disc material resist wear better than the matrix and will consequently wear the disc by abrasion, which adds to the friction.The above conclusions are drawn from a rather limited examination using only one set of test parameters. In fact, the two tests are both very flexible as to the way they can be used, and they both have advantages and limitations in tribological studies. They should rather be considered complementary than competitive.
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| 22. |
- Hentschel, Oliver, et al.
(author)
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Experimental Investigations in the Processing of AISI H11 Powder Blends Enriched with Tungsten Carbide Nanoparticles for the Additive Manufacturing of Tailored Hot Working Tools in the Directed Energy Deposition (DED-LB/M)—Impact of Tungsten Carbide Nanoparticles on Microstructural and Mechanical Characteristics
- 2024
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In: Metals. - : MDPI. - 2075-4701. ; 14:2, s. 188-188
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Journal article (peer-reviewed)abstract
- In this study, the DED-LB/M process of AISI H11 tool steel powder blends modified by adding WC nanoparticles (WC-np) in concentrations of 1, 2.5 and 5 wt.-% was the object of scientific investigations. For this, 30-layer cuboid specimens were manufactured. The overall scientific aim was to examine how the WC-np interact with the steel melt and in the end, influence the processability, microstructure and mechanical properties of produced specimens. The examinations were carried out on both as-built and thermally post-processed specimens. An advanced microstructural analysis (SEM, EDS, EBSD and XRD) revealed that due to the high solubility of WC-np in the molten steel, most of the WC-np appear to have dissolved during the ongoing laser process. Furthermore, the WC-np favor a stronger distortion and finer grain size of martensite in the manufactured specimens. An increase in hardness from about 650 HV1 for the H11 specimen to 780 HV1 for the one manufactured using the powder blend containing 5 wt.-% of WC-np was observed in as-built conditions. In the same way, the compression yield strength enhanced from 1839 MPA to 2188 MPA. The hardness and strength increasing effect of WC-np remained unchanged even after heat treatments similar to those used in industry.
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| 23. |
- Hentschel, Oliver, et al.
(author)
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Influence of the in-situ heat treatment during manufacturing on the microstructure and properties of DED-LB/M manufactured maraging tool steel
- 2023
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In: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 315
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Journal article (peer-reviewed)abstract
- Due to high productivity, additive manufacturing (AM), and especially Directed Energy Deposition using laser and metallic powder (DED-LB/M) is attractive for manufacturing tools with integrated functionalities. This investigation was dedicated to DED-LB/M manufacturing of experimental maraging tool steel, characterization of the build microstructure with advanced electron microscopy and evaluation of hardness properties. High printability and low porosity of the final builds were observed, relative density was not lower than 99.5% for specimens manufactured with 600 W and 800 W, but microstructure and properties of the build had a gradient along the height. The characteristic hardness profile and microstructure, which were dependent on the manufacturing parameters, were observed. The top layers of manufactured maraging steel samples had a structure of martensite with precipitates presumably formed during solidification. The top layers were therefore softer to the depth of the austenitization isotherm. The higher hardness was measured in the inner regions which was a result of an in-situ heat treatment that the manufactured material was subjected to during layer-by-layer manufacturing. Thermal cycles during manufacturing resulted in precipitation hardening effect in the inner regions. Scanning and transmission electron microscopy confirmed the formation film-like and round particles in the as-build material, in top and inner regions. However, the quasicrystalline nano-sized R′-phase precipitates were observed only in the inner regions. The formation of the R′-phase precipitated during manufacturing as a result of the in-situ heat treatment was discussed as a reason for higher hardness (440 – 450 HV1) measured in the inner regions.
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| 24. |
- Huber, Florian, et al.
(author)
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Systematic exploration of the L-PBF processing behavior and resulting properties of I3-stabilized Ti-alloys prepared by in-situ alloy formation
- 2021
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In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 818
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Journal article (peer-reviewed)abstract
- Aim of this work is to gain a comprehensive understanding of the effects of an increasing I3-phase stability of Tialloys on the L-PBF processing behavior. For this purpose, seven different Ti-alloys with an increasing concentration of the I3-phase stabilizing elements Fe and V were prepared by L-PBF and in-situ alloy formation. The Molybdenum equivalent (Moeq) of the examined alloys, as a measure of I3-phase stability, was varied systematically between -3.3 and 25. It is shown that a homogeneous distribution of elements is achievable by in-situ alloying. The experiments prove that the investigated alloys can be processed by a single L-PBF parameter set with high relative density above 99.8%. This finding is substantiated by calculated thermo-physical material properties and an analytical model. To understand the underlying metallurgical effects governing the L-PBF results, the samples were investigated extensively by EDS, EBSD, XRD, light microscopy and compression tests. The I3-phase fraction varies in dependence of the Moeq between 0% and 99%. Because of rapid solidification inherent in L-PBF a Moeq of 10 is sufficient to receive more than 90% I3-phase. The same amount of I3-phase after furnace cooling was only observed in alloys with Moeq of 20 or more. While all alloy compositions can be processed with high relative density of over 99.8%, alloys with a Moeq between 15 and 20 show a brittle material behavior in as-built state, resulting in cracking during L-PBF. This behavior is attributed to the formation of co-phase during L-PBF. In contrast, the highest I3-stabilized alloy with a nominal Moeq of 25 exhibits a very high ductility with a fracture strain exceeding 50%.
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| 25. |
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| 26. |
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| 27. |
- Jackman, Henrik, 1984-, et al.
(author)
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High resolution SEM imaging of carbon nanotubes : deconvolution and retrieval of intrinsic nanotube dimensions
- 2012
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Conference paper (peer-reviewed)abstract
- Characterizing physical properties of individual nanotubes is crucial for their implementation in nano electromechanical systems (NEMS). This requires measurements on suspended or free-standing structures together with accurate determination of the nanotubes dimensions. In situ methods are often used where physical measurements are performed inside electron microscopes [1-3]. Transmission electron microscopy (TEM) has the advantage of high resolution, providing accurate determination of both dimensions and the internal structure. The space inside a TEM is however rather restricted, leaving limited room for additional probes [4]. Scanning electron microscopy (SEM) on the other hand, has a large specimen chamber which facilitates the addition of probes, but the image resolution is lower, making the evaluation of material properties less accurate or even impossible for very thin nanotubes [1]. One way to solve this is to first measure the physical properties inside an SEM, and then determine the diameter using a TEM afterwards [1]. This approach requires transfer of the nanotube from the SEM to a suitable TEM sample holder, and analysis of the same sample-location in both instruments. It would thereby be advantageous to obtain accurate structural information directly inside the SEM [2]. We have studied the mechanisms involved in SEM image formation of small multiwalled nanotubes, 2-5 nm in diameter. The electron-probe shape in an SEM broadens the sample details, and the image can be seen as a convolution of the secondary electron yield at each sample position and the probe shape. By comparing SEM and TEM images, we found that the probe intensity profile was best described by a linear combination of Gaussian and Lorentzian distributions. Using the obtained probe shape, the SEM images could then be deconvoluted to reveal more details, including the inner diameter in some cases. We also show how the outer diameter can be obtained by differentiating image profiles, a method that does not require any detailed knowledge regarding the probe shape and is reliable down to dimensions comparable to the electron-probe size. This significantly improves the capabilities of in-situ SEM experiments by enabling accurate characterizations of nanofibres inside SEM instruments, without the need for subsequent TEM imaging
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| 28. |
- Jackman, Henrik, 1984-, et al.
(author)
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Measurements of the critical strain for rippling in carbon nanotubes
- 2011
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In: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 98:18, s. 3 pages-
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Journal article (peer-reviewed)abstract
- We report measurements of the bending stiffness in free standing carbon nanotubes, using atomic force microscopy inside a scanning electron microscope. Two regimes with different bending stiffness were observed, indicative of a rippling deformation at high curvatures. The observed critical strains for rippling were in the order of a few percent and comparable to previous modeling predictions. We have also found indications that the presence of defects can give a higher critical strain value and a concomitant reduction in Youngs modulus.
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| 29. |
- Javadzadeh Kalahroudi, Faezeh, et al.
(author)
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On the microstructure and high cycle fatigue of near-net shape PM-HIPed Inconel 625
- 2023
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In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 886
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Journal article (peer-reviewed)abstract
- This paper investigated the microstructure and fatigue behavior of PM-HIPed Inconel 625. The microstructure was composed of γ phase and (Mo, Nb) carbonitrides located mostly on prior particle boundaries. Despite the presence of these carbonitrides, the samples showed good tensile properties with high elongation. Two different surface conditions, pickled and machined, were used for high cycle fatigue testing under a four-point bending test. The results indicated that pickled samples had 6% lower fatigue strength (at 106 cycles) with three times higher standard deviation compared to the machined ones. Fatigue failure mechanisms were found to be dependent on surface conditions and showed different failure modes due to non-metallic oxide inclusions and surface defects in samples with machined and pickled surfaces, respectively. The effect of type, size, and location of defects, multiplicity of crack initiations, as well as surface roughness were analyzed and discussed.
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| 30. |
- Karlsson, Patrik, 1973-, et al.
(author)
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Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming
- 2012
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In: Lubrication Science. - : John Wiley & Sons. - 0954-0075 .- 1557-6833. ; 24:6, s. 263-272
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Journal article (peer-reviewed)abstract
- Adhesive accumulation of work material on the tool surface is today a major problem in many sheet metal-forming applications. Different laboratory test methods are used to investigate galling with respect to different tool materials, lubricants and process conditions. In the present study, the galling resistance of a modern nitrogen-alloyed powder metallurgy tool steel and an conventional ingot cast D2 type tool steel was evaluated under lubricated sliding against ferritic stainless steel sheets using a commercial pin-on-disc (POD) and an in-house made slider-on-flat-surface (SOFS) tribotester. The investigated tool steels ranked similarly in terms of galling resistanc in both test methods. However, sliding distances to galling were longer for the SOFS equipment due to continuous sliding on new lubricated sheet surface. Best performance was demonstrated by the powder metallurgy tool steel treated to 65 HRC. Differences in friction behaviour and galling initiation were analysed on the basis of the two different working conditions, i.e. open (SOFS) and closed (POD) tribosystems. Copyright © 2012 John Wiley & Sons, Ltd.
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| 31. |
- Karlsson, Patrik, 1973-, et al.
(author)
-
Influence of tool steel hard phase orientation and shape on galling
- 2014
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In: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 966-96, s. 249-258
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Journal article (peer-reviewed)abstract
- Conventionally manufactured cold work tool steel is often used in sheet metal forming as die material. Due to the forging process, the as-cast network structure of carbides is broken into elongated particles. Depending on the tool cross-section, the orientation and shape of carbides in the active tool surface is different. In the present research, the influence of tool steel hard phase orientation and shape on galling was investigated. D2 type tool steel was cut in three different orientations and tested in lubricated sliding conditions against AISI 304 austenitic stainless steel. Tests were performed using a Slider-On-Flat-Surface and galling was detected by changes in friction and post-test microscopy. The lubricant was Castrol FST8 using 5 g/m2 sheet material. Results showed a strong correlation between sliding distance to galling and tool steel hard phase orientation and shape at low loads, whereas high load contact resulted in early galling in all cases. Material transfer was observed mainly to the tool steel matrix. The worst performance was observed for specimens cut so that the tool steel hard phase, M7C3 carbides in the D2 steel, were oriented along the sliding direction, which resulted in longer open tool matrix areas contacting the sheet material.
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| 32. |
- Karlsson, Patrik, 1973-, et al.
(author)
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Influence of tool steel microstructure on friction and initial material transfer
- 2014
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In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 319:1-2, s. 12-18
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Journal article (peer-reviewed)abstract
- An investigation was conducted to study the influence of tool steel microstructure on initial material transfer and friction. Two different powder metallurgy tool steels and an ingot cast tool material were tested in dry sliding against 1.4301, 1.4162, Domex 355 MC and Domex 700 MC sheet materials. It was found that tool steel hard phase heights influence initial material transfer and friction. The coefficient of friction increased with decreasing tool steel hard phase heights at 50 N normal load and initial material transfer occurred around protruding hard phases. At higher load of 500 N the sheet material adhered to both the tool steel matrix and hard phases. Coefficient of friction decreased with increasing proof strength of the sheet material at 500 N normal load.
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| 33. |
- Karlsson, Patrik, 1973-
(author)
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The early stage of galling
- 2012
-
Licentiate thesis (other academic/artistic)abstract
- In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a kind of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, galling observed in contacts between tool steels and stainless steel sheets under lubricated sliding conditions was studied, focusing on the early stage of galling. It was found that changes in friction cannot be used as galling indicator in the early stage of galling because transfer and accumulation of sheet material happens even though friction is low and stable. The progression of galling is influenced by tool steel damage occurring around the tool steel hard phases caused by sheet material flow, which results in formation of wear-induced galling initiation sites. A correlation between the critical contact pressure to galling and sheet material proof stress was found. Galling happened at lower pressures for sheet material with lower proof stress possibly due to easier sheet material flow, resulting in quicker tool damage. Material transfer and tool steel damage were delayed for tool steels comprising homogenously distributed, small and high hard phases. Additionally, the galling resistance was higher for tool steels with higher hardness due to decreased tool steel damage. In a comparison between observations of the worn tool surfaces after wear tests and calculations in FEM it was found that material transfer did not take place at regions with highest contact pressures but at regions with highest plastic strains. The results obtained in this thesis indicate that tool steel damage and sheet material flow occurring in the contact during sliding are important factors influencing galling.
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| 34. |
- Karlsson, Patrik, 1973-
(author)
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The influence of tool steel microstructure on galling
- 2014
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Doctoral thesis (other academic/artistic)abstract
- In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a sort of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, the overall aim was to gain knowledge of the influence of tool steel microstructure on galling initiation under sliding conditions. It was discovered that material transfer and tool steel damage caused by sheet material flow creating wear-induced galling initiation sites occurred in the early stage of galling. The galling resistance was higher for tool steels with higher matrix hardness due to better resistance to tool steel damage. Initial friction and critical contact pressure to galling was influenced by the strength of the sheet material. Material transfer happened at low pressures and the friction value was high in a case of sheet materials with lower proof strength, possibly due to the sheet contact against the tool steel matrix resulting in high adhesion and quicker tool damage. It was demonstrated that, in addition to hardness of the tool steel matrix and sheet material proof strength, tool steel microstructural features like size, shape, distribution and height of hard phases are important parameters influencing galling. Tool steels comprising homogeneously distributed, small and high hard phases better prevented the contact between sheet material and the tool steel matrix. Thus, a metal to metal contact with high friction was more efficiently avoided, which resulted in better tool performance.
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| 35. |
- Kazantseva, N., et al.
(author)
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Martensitic transformations in Ti-6Al-4V (ELI) alloy manufactured by 3D Printing
- 2018
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In: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 146, s. 101-112
-
Journal article (peer-reviewed)abstract
- In the present investigation, Ti-6Al-4V ELI samples were manufactured by the powder-bed fusion (PBF) process using the laser sintering (LS) technology. Microstructure, chemical and phase constitution, and mechanical properties were studied by means of the transmission electron microscopy, atom probe tomography, X-ray diffraction, nanoindentation and mechanical testing. It was found that the structure of LS samples consisted of two different variants of metastable phases, namely the hexagonal α′ martensitic phase and small amounts of the orthorhombic α″ martensitic phase. The martensitic α′-phase was formed because of the high cooling rates of the LS method. The {101¯2} ⟨1¯011⟩ hexagonal martensite tensile twins were observed in the microstructure of the as-build alloy. Small areas with inner twinning martensitic plates, which are typical for the metastable orthorhombic martensitic phase in titanium alloys, were identified by the transmission electron microscopy. Atom probe tomography (APT) confirmed localization of β-stabilizing elements at interfaces, presumably at the twin or lamella boundaries. The structure and origin of the martensitic phases in 3D printed Ti-6Al-4V alloys are discussed with respect to in-situ heat treatment during manufacturing.
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| 36. |
- Kazantseva, Nataliya, et al.
(author)
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Micromechanisms of Deformation and Fracture in Porous L-PBF 316L Stainless Steel at Different Strain Rates
- 2021
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In: Metals. - : MDPI. - 2075-4701. ; 11:11
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Journal article (peer-reviewed)abstract
- The process of an unstable plastic flow associated with the strain rate sensitivity of mechanical properties was studied in porous 316L austenitic steel samples manufactured by laser powder bed fusion (L-PBF). Different micromechanisms of deformation and fracture of porous samples dependent on strain rate were found. It was found that despite the porosity, the specimens showed high strength, which increased with the loading rate. Porosity led to lower ductility of the studied specimens, in comparison with literature data for low porous 316L L-PBF samples and resulted in de-localization of plastic deformation. With an increase in strain rate, nucleation of new pores was less pronounced, so that at the highest strain rate of 8 x 10(-3) s(-1), only pore coalescence was observed as the dominating microscopic mechanism of ductile fracture.
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| 37. |
- Kazantseva, Natalia, et al.
(author)
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Oxygen and nitrogen concentrations in the Ti-6Al-4V Alloy manufactured by direct metal laser sintering (dmls) process
- 2017
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In: Materials letters (General ed.). - : Elsevier. - 0167-577X .- 1873-4979. ; 209, s. 311-314
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Journal article (peer-reviewed)abstract
- Two machines from two scientific centers (Russia and South Africa) were used for the manufacturing of the Ti6Al4V alloys by the direct metal laser sintering. The chemical composition of powders complies with the ASTM F-136 (grade 5), ASTM B348 (grade 23) standard for medical applications. Analysis of the oxygen and nitrogen contamination in DMLS alloys was done with Van de Graaff accelerator with two Mega Volts. It is found that structures of the samples manufactured with two different machines used the same regimes are close to each other. TEM studies found the metastable martensitic structure and silicon nitride Si3N4. It was found that the oxygen and nitrogen contents in both samples are within the normal range for medical grade titanium alloys.
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| 38. |
- Kazantseva, Natalia, et al.
(author)
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Twins in SLM Ti alloy
- 2017
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In: Titan. - : Mezhgosudarstvennaya Assotsyatsiya Titan. - 2075-2903. ; :2, s. 8-15
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Journal article (peer-reviewed)
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| 39. |
- Kazantseva, N. V., et al.
(author)
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Laser Additive 3D Printing of Titanium Alloys : Current Status, Problems, Trends
- 2021
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In: Physics of metals and metallography. - : Maik Nauka/Interperiodica. - 0031-918X .- 1555-6190. ; 122:1, s. 6-25
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Journal article (peer-reviewed)abstract
- Features of 3D printing, including laser melting of metal powders, were considered in this work. The effect of laser operation mode on the structure, residual stresses, and properties of manufactured metals was reviewed. A method for choosing process parameters using single tracks as universal for all types of metal laser 3D printers was proposed. Structural characteristics and medical requirements for biocompatible materials were presented. The biocompatible Ti-6Al-4V alloy manufactured by selective laser melting was considered.
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- Krakhmalev, Pavel, 1973-, et al.
(author)
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Effect of microstructure on edge wear mechanisms in WC-Co
- 2007
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In: International Journal of Refractory Metals and Hard Materials. - : Elsevier. - 0958-0611 .- 0263-4368. ; 25:2, s. 171-178
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Journal article (peer-reviewed)abstract
- Edge wear of nano to coarse WC–Co grades was investigated under two-body abrasion conditions using SiC abrasive at 2 and 15 N loads. With the fine abrasive utilized, a transition from homogeneous plowing in submicron grades to inhomogeneous grains pullout in coarse hardmetals was observed at the beginning stages. At final stages, plowing was detected in all the grades. When using the coarse abrasive, for all grades, flaking at the beginning and plowing at the final stages occurred. The performed numerical finite element simulation of the microstructural mechanical response showed good agreement to experimental results and was discussed in relation to the operative wear mechanisms observed. The found results demonstrated a remarkable influence of microstructure and abrasive size on the heterogeneous to homogeneous wear mechanisms transition at initial stages
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| 44. |
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| 45. |
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| 46. |
- Krakhmalev, Pavel, 1973-, et al.
(author)
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Functionalization of Biomedical Ti6Al4V via In Situ Alloying by Cu during Laser Powder Bed Fusion Manufacturing
- 2017
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In: Materials. - Basel : MDPI. - 1996-1944. ; 10:10
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Journal article (peer-reviewed)abstract
- The modern medical industry successfully utilizes Laser Powder Bed Fusion (LPBF) to manufacture complex custom implants. Ti6Al4V is one of the most commonly used biocompatible alloys. In surgery practice, infection at the bone-implant interface is one of the key reasons for implant failure. Therefore, advanced implants with biocompatibility and antibacterial properties are required. Modification of Ti alloy with Cu, which in small concentrations is a proven non-toxic antibacterial agent, is an attractive way to manufacture implants with embedded antibacterial functionality. The possibility of achieving alloying in situ, during manufacturing, is a unique option of the LPBF technology. It provides unique opportunities to manufacture customized implant shapes and design new alloys. Nevertheless, optimal process parameters need to be established for the in situ alloyed materials to form dense parts with required mechanical properties. This research is dedicated to an investigation of Ti6Al4V (ELI)-1 at % Cu material, manufactured by LPBF from a mixture of Ti6Al4V (ELI) and pure Cu powders. The effect of process parameters on surface roughness, chemical composition and distribution of Cu was investigated. Chemical homogeneity was discussed in relation to differences in the viscosity and density of molten Cu and Ti6Al4V. Microstructure, mechanical properties, and fracture behavior of as-built 3D samples were analyzed and discussed. Pilot antibacterial functionalization testing of Ti6Al4V (ELI) in situ alloyed with 1 at % Cu showed promising results and notable reduction in the growth of pure cultures of Escherichia coli and Staphylococcus aureus.
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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Krakhmalev, Pavel, 1973-, et al.
(author)
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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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In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 772
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Journal article (peer-reviewed)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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