Effect of Tungsten on Microstructure and Mechanical Properties of Novel NiMnCrMoW_x High-Entropy Alloys Developed by Mechanical Alloying

NiMnCrMoW_x (x = 0.2, 0.4, 0.6, 0.8, 1.0 atomic fraction) high-entropy alloys are synthesized by mechanical alloying and conventional sintering techniques. Both alloy powders and the sintered pellets are characterized for microstructural, chemical, and mechanical properties. The phase analysis by x-ray diffraction (XRD) and high-resolution transmission electron microscopy of 70 h milled powder confirmed the dual phase of BCC as a major phase and FCC as a minor phase. Scanning electron microscopy is used for microstructural study of the milled powders and sintered pellets. The differential scanning calorimetry analysis of milled powders confirmed that these are thermally stable below 1000 °C. The XRD of annealed powders didn’t show new phases below 1000 °C, whereas 1000 °C annealed powders showed the presence of σ-phase; the XRD of the sintered pellets confirmed different volume fractions of σ-phase, MoNi₃, and MnNi phase. Results of Vickers hardness and wear studies indicated that the alloy containing 0.6 atomic fraction of tungsten possessed a maximum hardness of 644 HV₅ and maximum wear resistance. This might be attributed to the maximum extent of the σ-phase, MoNi₃, and MnNi phases in the W_0.6 alloy.