The effect of changing constituents on tensile mechanical properties of HfNbTaTiZr high entropy alloy: A molecular dynamics study

The recent trend of high-entropy alloys (HEAs) was studied extensively for their promising mechanical properties, but individual constituents' effects have remained unexplored. In this work, the effects of changing the percentage of elements of HfNbTaTiZr-HEA on the mechanical properties were analyzed during uniaxial tension using molecular dynamics simulation. The tensile strength and modulus of elastic properties of the samples were analyzed. It was found that adding Nb or Ta up to 10 % (<i>i.e.</i> Nb10/Ta10) in the high entropy alloys increased the ultimate tensile strength (UTS) from 2.9 GPa in the base alloy to 3.8/3.9 GPa (Nb10/Ta10) respectively, but further increment of these elements to 30 % resulted in a downgrade of UTS to 2.7 GPa. Similarly, the modulus of elasticity increased from 117.7 (±3) GPa in the base alloy to 137.7/129 (±3) GPa (Nb10/Ta10) respectively, but fell to 112-115 GPa upon further increment. The initial increase in strength could be due to the solid solution strengthening mechanism. However, further increases in these elements might hinder the development of a homogeneous solid solution because of differences in atomic size and crystal structure, which could ultimately reduce the alloy's strength. However, the effect of Ti and Zr follows an opposite trend as compared to Nb and Ta. Furthermore, the optimum composition of HEAs alloys was analyzed using a surface-contour plot and suggests minimizing the inclusion of Ta for maximizing the UTS, E, and %Elongation. Also, the high-temperature behavior of the optimized HEA's alloy was analyzed which showed a deterioration in properties at elevated temperature. The fracture evolution of the samples showed cup and cone-type fractures propagating under strain, the linear thermal expansion coefficient of HfNbTaTiZr-HEA was also calculated and found closer to the literature value.