Microstructure and Mechanical Characteristics of µ-Plasma Additively Manufactured Equiatomic Ti–Nb–Zr–Mo–Ta HEA.

This paper reports on microstructure evolution, phase formation, microhardness, compressive stress–strain relationship, fractography, and sliding wear characteristics of multi-layer depositions of equiatomic Ti–Nb–Zr–Mo–Ta high entropy alloy (TNZMT HEA) by µ-plasma metal additive manufacturing (µ-PMAM) process. Microstructure evolution revealed that multi-layer deposition of TNZMT HEA comprises of major body centred cubic (BCC) phase having fine-dendritic structure and minor BCC phase having inter-dendritic structure. These phases are formed due to minor elemental segregation, higher cooling rates, and decomposition of single BCC phase. Microhardness of µ-PMAM deposited TNZMT HEA is 520 ± 10 HV which is much higher than the vacuum arc-melted TNZMT HEA. It is due to absence of dislocations and grain boundaries. Its Young's modulus, ultimate compressive strength, compressive yield strength, and compressive strain are found as 130 ± 4 GPa; 1892 ± 15.6 MPa; 1847 ± 25.8 MPa; and 13.53 ± 1.59% respectively. Minor decrease in stress is observed after yielding which may be due to dislocation unlocking by solute atoms or the ending of short-range order by dislocation motion. Its average coefficient of sliding friction, average worn-scar depth, and formation of macro-groove and delamination increases but specific wear rate decreases with the increase in applied load. Smaller values of applied load resulted in lesser wear debris which is confirmed by EDS analysis of the worn-surfaces. This study confirms that µ-PMAM deposited TNZMT HEA is a better knee implant material due to its better microstructure, smaller value of Young's modulus, larger compressive yield strength, higher microhardness, and improved sliding wear resistance. [ABSTRACT FROM AUTHOR]