Phase Stability of the intermetallic Heusler alloys of A2(Hf1-xZrx)Al where A=Pd and Pt

Abstract

First principles phase stability calculations are used to predict the lattice mismatches between Nb and the A(2)(Hf1-xZrx)Al L2(1) Heusler phases and the L2(1) phase formation energies, where A=Pd and/or Pt, and x=0, 0.25, 0.75 and 1. The calculated L2(1) phase mixing energy demonstrates that the Hf-Zr solution phases in the form of A(2)(Hf1-xZrx)Al (x not equal 0 and 1) are energetically favored, although the Zr-rich alloys exhibit a smaller lattice mismatch than the Hf-rich alloys. The introduction of Pt reduces the lattice mismatch, and forms the energetically favorable (PtPd)XAl Heusler phase, where X=Hf and Zr. A number of critical diffusion couple experiments confirm the phase stability predictions and establish new microstructural design parameters. (c) 2005 American Institute of Physics.