| 1. |
- Ahmed, R., et al.
(författare)
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Mapping the mechanical properties of cobalt-based stellite alloys manufactured via blending
- 2024
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Ingår i: Advances in Materials and Processing Technologies. - 2374-0698 .- 2374-068X. ; 10:3, s. 2531-2560
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Tidskriftsartikel (refereegranskat)abstract
- Stellite alloys have good wear resistance and maintain their strength up to similar to 600 degrees C, making them suitable for various industrial applications like cutting tools and combustion engine parts. This investigation was aimed at i) manufacturing new Stellite alloy blends using powder metallurgy and ii) mathematically mapping hardness, yield strength, ductility and impact energy of base and alloy blends. Linear, exponential, polynomial approximations and dimensional analyses were conducted in this semi-empirical mathematical modelling approach. Base alloy compositions similar to Stellite 1, 4, 6, 12, 20 and 190 were used in this investigation to form new alloys via blends. The microstructure was analysed using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Mechanical performance of alloys was conducted using tensile, hardness and Charpy impact tests. MATLAB (R) coding was used for the development of property maps. This investigation indicates that hardness and yield strength can be linked to the wt.% composition of carbon and tungsten using linear approximation with a maximum variance of 5% and 20%, respectively. Elongation and carbide fraction showed a non-linear relationship with alloy composition. Impact energy was linked with elongation through polynomial approximation. A dimensional analysis was developed by interlinking carbide fraction, hardness, yield strength, and elongation to impact energy.
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| 2. |
- Jabir Hussain, Ahmed Fardan, 1996, et al.
(författare)
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Numerical modelling of particle impact and residual stresses in cold sprayed coatings: A review
- 2021
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 409
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Forskningsöversikt (refereegranskat)abstract
- Cold spray technology provides protective coatings, additive manufacturing and repair to a wide array of industrial sectors. Alternative tags for cold spray include, kinetic metallisation, kinetic fusion, hypersonic spray, gas dynamic cold spray, cold spray printing, and cold spray additive manufacturing. These processes employ the same physics principles of accelerating micrometre-sized particles to supersonic velocities that impact and adhere onto a suitably prepared substrate. Numerical modelling has been used extensively to study particle impact modelling. The prediction of critical velocity, deformation mechanism and, more recently, residual stresses have been areas of interest that have been evaluated by numerical methods such as Lagrangian, Eulerian, Smoothed Particle Hydrodynamics, Coupled Eulerian-Lagrangian, and Molecular Dynamics. The crucial findings of these models are summarised, and their comparative outcomes assessed with a critical analysis of their merits and weaknesses. The process parameters applied in the simulations such as particle diameter, impact velocity, pre-heat temperature and material chemistry is compiled. The experimental techniques used for residual stress measurements; such as X-ray diffraction, neutron diffraction, material removal, curvature measurement and deformation techniques, are concisely reviewed from the context of being applied to cold spray deposits.
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| 3. |
- Deckers, Tobias, et al.
(författare)
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Impact of processing gas composition on process stability and properties of PBF-LB/M processed alloy 718
- 2024
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Ingår i: Journal of Manufacturing Processes. - 1526-6125. ; 120, s. 712-718
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Tidskriftsartikel (refereegranskat)abstract
- The almost unlimited design freedom of the laser-based powder bed fusion of metals (PBF-LB/M) makes this technology very attractive for industry. However, as a developing technology, it still faces some challenges when it comes to productivity and robustness, to name some. Whereas numerous studies covered the impact of laser-based parameters on material properties and robustness, the effect of the processing gas received limited attention. The objective of this study was to evaluate the effect of processing gas composition, containing helium (He) and hydrogen (H2), compared to conventionally used argon (Ar), during PBF-LB/M processing of virgin alloy 718 powder, on printing behavior and part properties. The four gases studied were Ar, Ar +30%He, Ar +30%He +2%H2, and Ar +70%He. Optical Tomography (OT) was used to monitor process stability, which unveiled a significant decrease in process-by products (spatters) between 51 % and 89 % using He and H2-containing gases. It was also found that the process gas decreased the bulk porosity from an average value of 0.08 % when processed with Ar to 0.04 % when using Ar + 70%He. The oxygen pickup by the spatter particles was reduced from 630 ppm (Ar) to 331 ppm (Ar +70%He). EBSD analysis revealed that there were no evident changes in microstructure with the processing gas. The samples processed also had similar tensile properties with yield and ultimate tensile strength of 1180 MPa and 1395 MPa, respectively. However, there was a slight increase in ductility from 16.5 % to 17.2 %, when processed with pure Ar and Ar + 70%He, respectively. This study shows that utilizing standard Ar processing atmosphere with He addition leads to a more stable process with reduced spatter, porosity and a marginal increase in ductility for Alloy 718.
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| 4. |
- Jabir Hussain, Ahmed Fardan, 1996, et al.
(författare)
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Effect of Part Thickness and Build Angle on the Microstructure, Surface Roughness, and Mechanical Properties of Additively Manufactured IN-939
- 2023
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 54:5, s. 1792-1807
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Tidskriftsartikel (refereegranskat)abstract
- Powder bed fusion-laser beam of metals (PBF-LB/M) has attracted significant interest due to the possibility of producing dedicated design features like thin-walled structures, even though their mechanical response and microstructure are not well understood. Hence, thin-walled IN-939 structures of different thicknesses (0.5, 1 and 2 mm) were manufactured at two build angles (90 and 45 deg) by PBF-LB/M. A preferred 〈100〉 crystallographic orientation was found along the build direction in all cases. The crystallographic texture intensity and surface roughness increased as the part thickness decreased for 90 deg and increased for 45 deg build angle. Reduction in wall thickness resulted in a decrease in the tensile properties, e.g., YS decreases by up to 33 pct and UTS decreases by up to 30 pct in comparison with the bulk specimen which had YS of 1051 ± 11 MPa and UTS of 1482 ± 9 MPa. Obtained results indicate that the apparent difference in tensile properties is primarily due to the overestimation of the load-bearing area. Two methods to estimate the accurate tensile properties based on roughness compensation are presented, using of which the corrected tensile performance of the thin-walled specimens was comparable with a standard tensile specimen.
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| 5. |
- Jabir Hussain, Ahmed Fardan, 1996, et al.
(författare)
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Fine-Tuning Melt Pools and Microstructures: Taming Cracks in Powder Bed Fusion—Laser Beam of a non-weldable Ni-base Superalloy
- 2024
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Ingår i: Materialia. - : ELSEVIER SCI LTD. - 2589-1529. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- Powder Bed Fusion – Laser Beam (PBF-LB) of high γ’ strengthened Ni-base superalloys, such as CM247LC, is of great interest for high temperature applications in gas turbines. However, PBF-LB of CM247LC is challenging due to the high cracking susceptibility during PBF-LB processing (solidification cracking) and heat treatment (strain age cracking, mostly caused by residual stresses). This study focuses on understanding the impact of process parameters on microstructure, residual stresses and solidification cracking. Laser power (P), speed (v) and hatch spacing (h) were varied while the layer thickness (t) was fixed. The melt pool size and shape were found to be key factors in minimizing solidification cracking. Narrower and shallower melt pools, achieved using a low line energy density (LED = P/v ≤ 0.1 J/mm), gave low crack densities (0.7 mm/mm2). A tight hatch spacing (h = 0.03 mm) resulted in reduced lack of fusion porosity. Electron backscatter diffraction investigations revealed that parameters giving finer microstructure with 〈100〉 crystallographic texture had low crack densities provided they were processed with a low LED. Atom probe tomography elucidated early stages of spinodal decomposition in the as-built condition, where Cr and Al cluster separately. The extent of spinodal decomposition was found to be affected by the LED and the hatch spacing. Samples with low LED and small hatch spacing showed higher degrees of spinodal decomposition. X-ray diffraction residual stress investigations revealed that the residual stress is proportional to the volumetric energy density (VED = P/(v. h. t)). Although low residual stresses can be achieved by using low VED, there is a high risk of lack of fusion. Hence, other parameters such as modified scan strategy, build plate pre-heating and pulsed laser mode, must be further explored to minimize the residual stresses to reduce the strain age cracking susceptibility.
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| 6. |
- Jabir Hussain, Ahmed Fardan, 1996
(författare)
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Powder Bed Fusion – Laser Beam of a non-weldable Ni-base superalloy: Role of process parameters and scan strategies
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM), in particular, Powder Bed Fusion – Laser Beam (PBF-LB) has garnered attention due to its design freedom, near net shape capability, and reduced lead time. Ni-base superalloys are a class of materials used for high temperature applications and widely utilized in the energy and aerospace sectors. However, only a limited number of Ni-base superalloys can be manufactured defect-free through the PBF-LB process. This is especially true for non-weldable Ni-base superalloys such as CM247LC which are susceptible to hot cracking and solid-state cracking. This is an issue that needs to be addressed for increased utilization of these alloys to manufacture complex components by PBF-LB. This thesis explores strategies that can enable PBF-LB processing of CM247LC with minimal or no hot cracking (solidification cracking) and low residual stresses. The first part of the thesis explores the impact of main process parameters such as laser power, speed, and hatch spacing on solidification cracking, microstructure, and residual stresses. The results from the first part indicate that low solidification cracks are achieved for low line energy density (ratio of laser power and speed) and low hatch spacing. This is due to the shallower melt pools achieved and its effect on solidification structure and in turn grain morphology/texture. The residual stresses are found to be proportional to the volumetric energy density. The second part of the thesis explores the impact of scan strategies on solidification cracking, microstructure, and residual stresses. This was done as the results from the first part of the thesis indicated that the solidification cracking and residual stresses could not be reduced solely by optimizing laser power, speed, and hatch. Therefore, the study varied the stripe width with optimized laser parameters. The results seemed to be promising for a short stripe width of 0.2 mm that gave lower solidification cracking and residual stresses. The decrease in solidification cracking has been attributed to the modification in melt pool size/shape and the mushy zone length. The lower residual stresses were possibly caused by the increased re-melting which led to residual stress relief. The results from the thesis provide an improved understanding of solidification cracking and residual stress mechanisms in non-weldable Ni-base superalloys manufactured by PBF-LB. The presented results can enable PBF-LB processing of alloys susceptible to hot and solid-state cracking.
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| 7. |
- Mohammadzdeh, Ahad, et al.
(författare)
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A novel alloy design approach in developing CoNi-based high entropy superalloy using high entropy alloys thermodynamic and spark plasma sintering
- 2024
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - 0921-5093. ; 909
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Tidskriftsartikel (refereegranskat)abstract
- This study introduces an innovative alloy design strategy by integrating HEAs principles to develop CoNi-based high entropy superalloys (HESAs). The powder of designed HESA produced using gas atomization and consolidated using spark plasma sintering (SPS). The alloy design strategy validated by CALPHAD to mitigate detrimental phase precipitation and segregation during powder production, material consolidation, and post-processing heat treatments. CoNi-HESA powder with a calculated mixing entropy of 1.568R was successfully developed and consolidated using SPS. Optimization of SPS parameters at 1175 °C, 10 min, and 100 °C/min achieved a relative density of 99.9 %. Subsequent heat treatments further improved the material's characteristics. Solutionizing at 1190 ± 10 °C for 2 h with water quenching resulted in a fine grain structure of ∼7 μm grain size. Aging at 900 °C for 24 h, followed by water quenching, yielded uniformly distributed fine γ′ precipitates comprising approximately 65 % of the γ matrix, without unwanted secondary precipitates or TCP phases. This study demonstrates the effectiveness of the novel approach in designing CoNi-based HESAs and optimizing their properties through careful process parameter selection and post-heat treatment cycles. The combination of thermodynamic calculations, HEA principles, and powder metallurgy techniques offers a promising approach for developing advanced high entropy superalloys with tailored microstructures.
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