| 1. |
- 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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| 2. |
- Karlsson, Dennis, et al.
(författare)
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Structure and phase transformations in gas atomized AlCoCrFeNi high entropy alloy powders
- 2022
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 893
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the crystal structure and phase stability of gas atomized equiatomic AlCoCrFeNi powder was investigated. This alloy is usually described as a high entropy alloy forming a solid solution phase stabilized by a high mixing entropy. However, thermodynamic calculations show that the high entropy phase is stable only at very high temperatures close to the melting point and that a mixture of several phases are the most stable state at lower temperatures. This suggest that kinetic effects may influence the phase composition of atomized powder. The unique features of X-ray diffraction, neutron diffraction as well as transmission electron microscopy were used to study the atomic structure of the atomized powder in detail. The results show that the powder crystallises in an ordered B2 (CsCl-type) structure with a preferred site occupation of Al and Fe on the (1/2 1/2 1/2) position and Co and Ni on the (0 0 0) position. During heat-treatment of the powder, the B2 phase decomposes into fcc and sigma phases and the final phase composition is highly dependent on the heating rate. The effect of heat-treatment on the atomized powder was also investigated and revealed a significant phase transformation with e.g. the formation of sigma phase preferably at the surface of the powder particles. The phase content was also dependent on the size fraction of the powder particles. Sintering of green bodies made with different heat cycles showed that the phase composition of the starting material had a significant impact on the final phase composition and microstructure of the sintered components. The results illustrate the importance of well-defined powder materials for powder consolidation, especially additive manufacturing (binder jetting) of high entropy alloys.
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| 3. |
- Larsen, Simon R., et al.
(författare)
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Magnetic properties and thermal stability of B2 and bcc phases in AlCoCrFeMnxNi
- 2021
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 861
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Tidskriftsartikel (refereegranskat)abstract
- Alloys of AlCoCrFeMnxNi (x = 0.0, 0.04, 0.08, 0.12 and 0.16) have been synthesized through arc-melting and gas atomisation (x = 0.0 and 0.16) to investigate the effect of Mn additions to AlCoCrFeNi. Here, the structure, magnetic properties and the thermal stability of the alloys is presented. Electron microscopy confirmed the elemental composition and revealed the microstructure to consist of two spinodally decomposed phases. Rietveld analysis of standard powder X-ray diffraction showed the arc-melted samples consisted of two phases, a B2 phase and a bcc phase while the gas atomised powders consisted of a singlephased B2 structure. Magnetic measurements revealed an increase in the saturation magnetisation at room temperature by 68% for AlCoCrFeMnNi compared to AlCoCrFeNi. The thermal stability of the alloys was investigated using magnetometry, differential scanning calorimetry and in-situ X-ray diffraction, which showed that an increase in Mn content adversely effected the thermal stability of the alloy.
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| 4. |
- Lin, C., et al.
(författare)
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Nano Pores Evolution in Hydroxyapatite Microsphere during Spark Plasma Sintering
- 2011
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Ingår i: Science of Sintering. - 0350-820X. ; 43:1, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- Micron-spherical granules of hydroxyapatite (HAp) nanoparticles were prepared by powder granulation methods. Through subsequent sintering, porous HAp microspheres with tailored pore and grain framework structures were obtained. Detailed microstructure investigation by SEM and TEM revealed the correlation of the pore structure and the necking strength with the sintering profiles that determine the coalescence features of the nanoparticles. The partially sintered porous HAp microspheres containing more than 50% porosity consisting of pores and grains both in nano-scale are active in inducing the precipitation of HAp in simulated body fluid. The nano-porous HAp microspheres with an extensive surface and interconnecting pores thus demonstrate the potential of stimulating the formation of collagen and bone and the integration with the newly formed bones during physiological bone remodeling.
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| 5. |
- Mishra, Pragya, 1989-, et al.
(författare)
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Microstructural Characterization and Mechanical Properties of L-PBF Processed 316 L at Cryogenic Temperature
- 2021
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Ingår i: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 14:19
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Tidskriftsartikel (refereegranskat)abstract
- Laser powder bed fusion (L-PBF) has attracted great interest in the aerospace and medical sectors because it can produce complex and lightweight parts with high accuracy. Austenitic stainless steel alloy 316 L is widely used in many applications due to its good mechanical properties and high corrosion resistance over a wide temperature range. In this study, L-PBF-processed 316 L was investigated for its suitability in aerospace applications at cryogenic service temperatures and the behavior at cryogenic temperature was compared with room temperature to understand the properties and microstructural changes within this temperature range. Tensile tests were performed at room temperature and at −196 °C to study the mechanical performance and phase changes. The microstructure and fracture surfaces were characterized using scanning electron microscopy, and the phases were analyzed by X-ray diffraction. The results showed a significant increase in the strength of 316 L at −196 °C, while its ductility remained at an acceptable level. The results indicated the formation of ε and α martensite during cryogenic testing, which explained the increase in strength. Nanoindentation revealed different hardness values, indicating the different mechanical properties of austenite (γ), strained austenite, body-centered cubic martensite (α), and hexagonal close-packed martensite (ε) formed during the tensile tests due to mechanical deformation.
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| 6. |
- Zheng, Qiye, et al.
(författare)
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High Contrast Thermal Conductivity Change in Ni-Mn-In Heusler Alloys near Room Temperature
- 2019
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Ingår i: Advanced Engineering Materials. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1438-1656 .- 1527-2648. ; 21:5
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Tidskriftsartikel (refereegranskat)abstract
- Materials with an abrupt transition between a low and a high thermal conductance state at a critical temperature would be useful for thermal regulation applications. Here, the authors report a high contrast reversible thermal conductivity change through the thermally-induced martensitic transition (MT) in Ni-Mn-In alloys. The authors measure the thermal conductivity of a wide temperature range 130 < T < 530 K using time-domain thermoreflectance (TDTR). The thermal conductivity of these alloys increases from ≈7.0-8.5 W m−1 K−1 to ≈11.5-13.0 W m−1 K−1 through the MT near 300 K as temperature rises, with a rate of change among the highest yet reported in solid-state materials with thermally-induced phase transitions. Based on Hall resistivity measurements, the authors further show that the change of thermal conductivity is dominated by the electronic contribution, which results from a unique carrier mobility change through the MT. Their findings highlight the interplay between the structural disorders and the thermal transport in alloys through solid-state phase transitions and open a new avenue in the search of high-performance materials for thermal regulation. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 7. |
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| 8. |
- Zhong, Yuan, et al.
(författare)
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Additive manufacturing of ITER first wall panel parts by two approaches : Selective laser melting and electron beam melting
- 2017
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Ingår i: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 116, s. 24-33
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Tidskriftsartikel (refereegranskat)abstract
- Fabrication of ITER First Wall (FW) Panel parts by two additive manufacturing (AM) technologies, selective laser melting (SEM) and electron beam melting (EBM), was supported by Fusion for Energy (F4E). For the first time, AM is applied to manufacture ITER In-Vessel parts with complex design. Fully dense SS316L was prepared by both SLM and EBM after developing optimized laser/electron beam parameters. Characterizations on the density, magnetic permeability, microstructure, defects and inclusions were carried out. Tensile properties, Charpy-impact properties and fatigue properties of SLM and EBM SS316L were also compared. ITER FW Panel parts were successfully fabricated by both SLM and EBM in a onestep building process. The SLM part has smoother surface, better size accuracy while the EBM part takes much less time to build. Issues with removing support structures might be solved by slightly changing the design of the internal cooling system. Further investigation of the influence of neutron irradiation on materials properties between the two AM technologies is needed.
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| 9. |
- Campanini, Donato, et al.
(författare)
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Raising the superconducting T-c of gallium : In situ characterization of the transformation of alpha-Ga into beta-Ga
- 2018
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:18
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Tidskriftsartikel (refereegranskat)abstract
- Gallium (Ga) displays several metastable phases. Superconductivity is strongly enhanced in the metastable beta-Ga with a critical temperature T-c = 6.04(5) K, while stable alpha-Ga has a much lower T-c < 1.2 K. Here we use a membrane-based nanocalorimeter to initiate the transition from alpha-Ga to beta-Ga on demand, as well as study the specific heat of the two phases on one and the same sample. The in situ transformation is initiated by bringing the temperature to about 10 K above the melting temperature of alpha-Ga. After such treatment, the liquid supercools down to 232 K, where beta-Ga solidifies. We find that beta-Ga is a strong-coupling type-I superconductor with Delta(0)/k(B)T(c) = 2.00(5) and a Sommerfeld coefficient gamma(n) = 1.53(4) mJ/molK(2), 2.55 times higher than that in the alpha phase. The results allow a detailed comparison of fundamental thermodynamic properties between the two phases.
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| 10. |
- Dalou, Celia, et al.
(författare)
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Redox control on nitrogen isotope fractionation during planetary core formation
- 2019
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 116:29, s. 14485-14494
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Tidskriftsartikel (refereegranskat)abstract
- The present-day nitrogen isotopic compositions of Earth's surficial (N-15-enriched) and deep reservoirs (N-15-depleted) differ significantly. This distribution can neither be explained by modern mantle degassing nor recycling via subduction zones. As the effect of planetary differentiation on the behavior of N isotopes is poorly understood, we experimentally determined N-isotopic fractionations during metal-silicate partitioning (analogous to planetary core formation) over a large range of oxygen fugacities (Delta IW -3.1 < logfO(2)
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