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[The Minerals, Metals & Materials Series] TMS 2020 149th Annual Meeting & Exhibition Supplemental Proceedings || Critical Quenching Rates After Solution Annealing: Peculiarities of Aluminuma??Silicon Alloys Fabricated by Laser Powder-Bed Fusion
摘要： Hot isostatic pressing is commonly used to reduce the porosity of (sand-)cast age-hardenable Al-alloys in order to meet the high quality requirements defined by aircraft and automotive industries. In order to establish additive manufacturing methods, such as laser powder-bed fusion (L-PBF), hot isostatic pressing can be utilized to reduce the anisotropic mechanical properties in as-built condition and at the same time eliminate porosity. For the cast aluminum alloy A356, a gas pressure of 75 MPa during hot isostatic pressing lowers the critical cooling rate required to achieve an oversaturated solid solution to about 1 K/s, which is significantly lower than the required quenching rate at atmospheric pressure (2–4 K/s). Thus, an oversaturated state of dissolved magnesium and silicon atoms within the aluminum matrix of cast alloys can easily be achieved in modern hot isostatic presses, thereby avoiding the necessity of a separate solution annealing step. In this work, we applied hot isostatic pressing followed by rapid quenching and direct aging to age-hardenable aluminum alloys processed by both sand casting and laser powder-bed fusion. It was shown that the proposed process of direct aging could be utilized for post-heat treatment of additively manufactured age-hardenable aluminum alloys to open up new fields of applications, for which components have to possess a high fatigue resistance.
关键词： Hot isostatic pressing,Critical cooling rate,Additive manufacturing,Fatigue resistance,Laser powder-bed fusion,Selective laser melting
更新于2025-09-23 15:19:57
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Dielectric and Ferroelectric Properties of P(VDF-TrFE) Films with Different Polar Solvents
摘要： We investigated the structural, dielectric, and ferroelectric properties of poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] films that were grown using dimethylformamide (DMF) and tetrahydrofuran (THF) polar solvents. The DMF solvent has a large dipole moment with a long bond length and evaporates slowly while the THF solvent has a small dipole moment with a short bond length and evaporates rapidly. Because of these differences, a thin film with a rough surface occurs when using DMF while a thick film with a smooth surface is formed when using THF. Compared to DMF solvent, the ferroelectric polarization is not well saturated and the dielectric constant is quite low for the THF solvent, which is possibly due to the residual paraelectric defects in the P(VDF-TrFE) films. For both solvents, the polarization switching can be explained by using the Kolmogorov-Avrami-Ishibashi (KAI) model with similar switching times. Both solvents enable the P(VDF-TrFE) films to have good retention and fatigue resistance for ferroelectric polarization.
关键词： Polar solvents,P(VDF-TrFE),Fatigue resistance,Ferroelectric switching,Retention
更新于2025-09-19 17:15:36
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Influence of Work Media on Surface Property of Compacted Graphite Cast Iron Processed by Laser Local Processing
摘要： In order to enhance surface property of brake materials, compacted graphite cast iron (CGI) with non-smooth surface was processed by laser local processing. This study focuses on the influence of the work media on wear resistance and thermal fatigue resistance of specimens. The results showed that when the work media were air and water respectively, laser local processing could enhance surface property of CGI. Changing work media could not change phase compositions of the laser processing area, but refined their microstructures, which enhanced their micro-hardness. By this way, the specimens’ wear resistance and resistance to thermal crack initiation were further improved, while their resistance to thermal crack propagation was influenced by cracks on bionic units.
关键词： Work media,Laser,Compacted graphite cast iron,Wear resistance,Thermal fatigue resistance
更新于2025-09-16 10:30:52