Effect of WC addition on microstructure and properties of powder metallurgy CoCrNi medium entropy alloy

Abstract

To surpass the current level of mechanical properties exhibited by CoCrNi medium-entropy alloys (MEA), (CoCrNi)100−x(WC)x (x = 0, 2, 4 and 6 for molar ratio) MEA samples were prepared using powder metallurgy with atomized powder as the raw material, and the influence of WC content on the microstructural evolution and mechanical properties of the sintered MEAs was investigated. As the WC content increased, the phase structure of the sintered MEAs changed from a single FCC phase to an FCC+Cr23C6 phase, while the grain size of the matrix decreased. Consequently, the strength of the alloy exhibited significant improvement. For instance, the tensile yield and fracture strengths of (CoCrNi)98(WC)2 were measured at 574 and 971 MPa, respectively, while maintaining a plasticity of approximately 41.6%. Furthermore, the addition of WC led to a considerable increase in the hardness for (CoCrNi)94(WC)6, reaching 314.7 HV, which was nearly 50% higher than that of the CoCrNi matrix. The increased hardness proved beneficial in enhancing the material’s wear resistance, which first increased and then decreased. The wear mechanisms primarily involved abrasive and oxidation wears. The observed increase in yield strength can be attributed to the combined effects of multiple strengthening mechanisms. The individual contributions of these mechanisms were quantitatively evaluated and compared to the actual values, demonstrating consistency with the calculated results. Notably, solid-solution strengthening emerged as the principle strengthening mechanism.