Refractory High Entropy Alloys for High Temperature Structural Applications
PI - Prof. B. S. Murty (IIT Madras)
This project was sponsored by the United States Air Force Research Laboratory with Prof. B. S. Murty of the Indian Institute of Technology Madras as PI. Dr. Lavanya Raman (then PhD Research Scholar with Prof. Murty) and I together worked on this project.
I studied 126 quaternary and 126 quinary equiatomic refractory high entropy alloys (RHEA) made from Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta), and Group VI (Cr, Mo, W) elements. We used Rule-of-mixtures (ROM) technique to calculate liquidus temperature, density (ρ), Young’s modulus (E), % atomic size difference (δ), valence electron concentration (VEC), and specific heat at constant pressure and at 1273 K (Cp). CALPHAD technique is used (thanks to V. S. Hariharan) to predict the number of phases formed at 298 K, ρ, and liquidus temperature.
We found that the ROM calculated densities match perfectly with CALPHAD values. Densities and E are directly proportional to the VEC and liquidus temperature of the alloys. Ti, Zr, and Hf are ductilizing the alloys and making them light; whereas Cr, Mo and W are reducing the alloys’ ductility and making them heavy. For quinary RHEAs, Cp showed six distinct groups with δ, but a similar trend was not observed in quaternary RHEA. Here we used scatter matrix methodology to screen a large number of alloys based on various properties.
The numbers in blue in the above figures show the Pearson’s correlation coefficient. The 6 distinct groups in δ vs. Cp graph of quinary RHEA needs further research. Some of the findings from this work were later proved by experimental and/or DFT simulations by different researchers. The addition of HCP elements was shown to increase the Pugh’s ratio
This work resulted in a publication
