Mechanically alloyed and spark plasma sintered WNbMoVTa refractory high entropy alloys: Effects of Cr and Al on the microstructural and mechanical properties

In this study, WNbMoVTa refractory high entropy alloys (RHEAs) with a body-centered cubic structure (BCC) were produced in the presence of Cr and Al additions using mechanical alloying (MA) and spark plasma sintering (SPS) methods. Firstly, MA was conducted on the WNbMoVTa powders at different durations (2, 4, 6, and 8 h), and a single BCC phase was observed after MA for 2 h. The average crystallite size, lattice strain, and particle size for the 6 h MA'ed powders were measured as similar to 8.10 nm, similar to 2.50%, and similar to 400 nm, respectively. Based on the analyses of the WNbMoVTa powders, 6 h was chosen as the optimum MA time. Secondly, different amounts of Cr and Al elements were added into the WNbMoVTa powders, and they were converted into WNbMoVTaCrxAly (x, y = 0, 0.5, 1.0 wt%) powders. Lastly, they were MA'ed for 6 h and SPS'ed at 1500 degrees C under 30 MPa for 10 min. Composition, microstructure, density, microhardness, wear resistance, and thermal behavior properties were examined for all the sintered samples. MAed and SPS'ed WNbMoVTa samples showed the lowest microhardness (10.82 +/- 0.12 GPa) and the highest wear volume loss (1.25 x10(-4) mm(3)) values. After additions of Cr and Al elements into the WNbMoVTa, microhardness increased to a maximum value of 13.06 +/- 0.18 GPa, and wear volume loss decreased to a minimum value of 0.16 x 10(-4) mm(3). Also, the weight gain of the WNbMoVTa sample in the air decreased by adding Al and Cr elements. Thus, the mechanical and thermal properties of the WNbVMoTa sample were enhanced with the incorporating of Al and Cr elements.