In this study, tensile and creep deformation of a high-entropy alloy processed by selective laser melting (SLM) has been investigated; hot ductility drop was identified at first, and the loss of ductility at elevated temperature was associated with intergranular fracture. By modifying the grain boundary morphology from straight to serration, the hot ductility drop issue has been resolved successfully. The serrated grain boundary could be achieved by reducing the cooling rate of solution heat treatment, which allowed the coarsening of L1
2
structured γ′ precipitates to interfere with mobile grain boundaries, resulting in undulation of the grain boundary morphology. Tensile and creep tests at 650°C were conducted, and serrated grain boundary could render a significant increase in tensile fracture strain and creep rupture life by a factor of 3.5 and 400, respectively. Detailed microstructure analysis has indicated that serrated grain boundary could distribute strains more evenly than that of straight morphology. The underlying mechanism of deformation with grain boundary serration was further demonstrated by molecular dynamic simulation, which has indicated that serrated grain boundaries could reduce local strain concentration and provide resistance against intergranular cracking. This is the first study to tackle the hot ductility drop issue in a high-entropy alloy fabricated by SLM; it can provide a guideline to develop future high-entropy alloys and design post heat treatment for elevated temperature applications.
Recently, novel high‐entropy alloys (HEAs) of Al–Co–Cr–Fe–Ni–Ti systems containing face‐centered cubic (FCC) matrix and γ′ precipitates (L12 phase) have been studied. They show superior mechanical properties at room (298 K) and cryogenic temperatures (77 K). Herein, microstructure deformation and fracture after tensile strain are investigated. The results show that multiple‐layered stacking faults occur after the tensile test at 77 K, which can increase the yield strength and ultimate tensile strength by 20% and 24%, respectively. The γ′ precipitates become disordered after the alloy deforms at 77 K, which decreases the formation barrier of mechanical twinning and increases ductility at 77 K by 27%.
Based on multi-component alloys using precipitation hardening, a Cu-Ni-Si-Fe copper alloy was prepared and studied for hardness, electrical conductivity, and wear resistance. Copper Nickel Silicon (Cu-Ni-Si) intermetallic compounds were observed as precipitates, leading to an increase in mechanical and physical properties. Further, the addition of Fe was discussed in intermetallic compound formation. Moreover, microstructures, age hardening, and dry sliding wear resistances of the present alloy were analyzed and compared with C17200 beryllium copper. The results showed that the present alloy performed extraordinarily, with 314 HV in hardness and 22.2 %IACS in conductivity, which is almost similar to C17200 alloy. Furthermore, the dry sliding wear resistance of the present alloy was 2199.3 (m/MPa*mm3) at an ambient temperature, leading to an improvement of 208% compared with the C17200 alloy.
The welding technology is significant for application of high-entropy alloys (HEAs) in the industry. In this study, the mechanical properties and microstructures of Al0.2Co1.5CrFeNi1.5Ti0.3 after welding by gas tungsten arc (GTA) welding and friction stir welding (FSW) are discussed, respectively. GTA welding of precipitated HEAs resulted in the formation of dendrites in the fusion zone; the hardness and tensile strength of the GTA weld decreased to 68% and 51% compared to the base metal, respectively. However, FSW exhibited excellent mechanical properties, which were still over 94% of the hardness value and tensile strength of the base metal. The microstructure was characterized by discontinuous dynamic recrystallization and the grain refinement effect in the stir zone. The microstructure of the two welds resulted in different mechanical properties. The weld after FSW was strengthened by the grain refinement strengthening, which almost compensates the decrease in hardness caused by the re-dissolution of all precipitates in the stir zone, while the dendritic structure strongly affected the mechanical properties and softened the fusion zone after the GTA process. During the tensile test, the digital image correlation was conducted simultaneously. It shows that the GTA weld had lower strength with nonuniform deformation in the fusion zone, while the FSW weld showed higher strength with uniform deformation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.