Equilibrium between MB2 (M=Ti,Zr,Hf) UHTC and Ni: A thermodynamic database for the B–Hf–Ni–Ti–Zr system

MB2 (M=Ti,Zr,Hf) Ultra High Temperature Ceramics (UHTCs) are characterised by melting temperatures in excess of 3000 °C and have structural, physical, transport, and thermodynamic properties suitable for use as thermal barriers in extreme environments. It is then necessary to investigate interactions of the diborides with the materials they are supposed to protect. To this end it has been developed a CALPHAD thermodynamic database for the calculation of phase equilibria and thermodynamic properties in the quinary system BNiTiZrHf. The database contains thermodynamic parameters for all the phases included in the 10 binary and 10 ternary sub-systems of BNiTiZrHf. A few binary systems (BHf, BTi, BZr, HfNi, NiZr) have been slightly modified with respect to the previous assessments and several ternary systems (BHfNi, BNiTi, BNiZr, BHfZr, BTiZr, HfNiTi, HfNiZr, HfTiZr, NiTiZr) have been completely assessed or re-assessed in this work with particular attention to the self-consistency of the models adopted.