Mechanical behavior and deformation mechanisms in a single-phase face-centered cubic VMnFeCoNi high-entropy alloy

• Applicant: Dr.-Ing. Aditya Srinivasan Tirunilai
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553555345

The present project aims at a comprehensive analysis of the physical and mechanical properties, as well as the general deformation behavior of the equiatomic VMnFeCoNi high-entropy alloy. In the preliminary work, the alloy was synthesized in a standard state with a single-phase face-centered cubic (FCC) microstructure, which was achieved for the first time. The novelty is not limited to the single-phase nature of the alloy, formerly thought to exist only as two-phase FCC+σ, but also to its excellent mechanical properties. The project seeks to gain insight into this promising structural alloy (based on preliminary results), whose properties at room temperature (RT), including yield stress, work hardening rate, and ductility are superior to those of the thoroughly studied Cantor alloy (CrMnFeCoNi). Moreover, the post-rupture microstructural characterization reveals that VMnFeCoNi only experiences dislocation-based deformation at RT, and surprisingly no twinning or transformation-induced plasticity (TWIP or TRIP) despite its excellent work hardening capability and strength-ductility combination. Indeed, TWIP and TRIP were thought to be prerequisites for such properties, as seen primarily in the deformation behavior of the Cantor alloy and its subsets, especially CrCoNi. Thus, the origins of the strong and stable work-hardening rate of VMnFeCoNi at RT, and the possibility of TWIP/TRIP at lower temperatures are key points of interest. In addition, a comprehensive analysis necessitates the determination of physical properties (thermophysical properties, elastic constants, stacking fault energy (SFE)) without which the mechanical properties cannot be effectively rationalized. Finally, considering that short-range order (SRO) may form, as suggested in other V-containing alloys, (i) the existence of SRO in VMnFeCoNi and (ii) its potential effect on mechanical properties will be investigated. Preliminary data indicate that the deformation behavior of VMnFeCoNi and VCoNi is superior to that of CrMnFeCoNi and CrCoNi, respectively. This motivates a systematic comparison of these alloys to investigate the effect of V and Cr on solid solution hardening, SFE, active deformation mechanisms, etc.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partner: Jean-Charles Stinville, Ph.D.