Bimodal structure, strength-plasticity synergy and exceptional wear behavior in the spark plasma sintered (CoCrFeNi)84(AlTi)16 medium/high entropy alloy systems

Abstract

Medium/high entropy alloy (M/HEA) system compositions are promising in wear resistance with comprehensive mechanical performance to meet the demands of practical engineering and technological applications as a multi-functional material. Nevertheless, for nano/ultrafine grained M/HEAs, there is still rather limited consideration of the friction and wear performance. In the current work, we present a strategy to develop a spark plasma sintered (SPSed) (CoCrFeNi)₈₄(AlTi)₁₆ M/HEAs with low density, strength-plasticity synergy and excellent wear resistance via adjusting the heterogeneous bimodal and nanocrystalline structure of coupled medium/high entropy solid solution phases with proximate equal volume fraction in the presence of multicomponent submicron/nanometer intermetallic phases. The multiple scales-component-phase-driven structure of the (CoCrFeNi)₈₄(AlTi)₁₆ M/HEA systems results in superior mechanical properties for the 3 M/HEA system, where the micro hardness value, compressive yield strength (CYS), the ultimate compressive strength (UCS), the fracture strain (FS) and the specific yield strength are obtained about 676 HV, 1730 MPa, 2095 MPa, 11.5 % and 0.238 GPa cm³/g, respectively. Low coefficient of friction (low COF) of 0.17 and wear rate (WR) of 0.1 × 10⁻⁵ mm³N⁻¹m⁻¹ are achieved for the 3 M/HEA system, which are much lower than the reported M/HEAs and traditional wear resistance alloy. It is affected by synergy effect of hardness via the BCC phase, work hardenability and plastic deformation of FCC phase. For the 3 M/HEA system, the wear morphology is clearly detected as a smoother surface with the shallower grooves, representing that the main wear mechanism is an abrasive wear. Therefore, developing similar multiple scales-component-phase-driven structures may open an avenue for further optimization of the mechanical/wear performance of the M/HEA systems.