Wettability of by molten Ni(B) alloys interpreted by CALPHAD methods, Part 2: Wetting and interfacial reactivity

This study presents data on the wettability and the interfacial characteristics of HfB2 ceramics, in contact with liquid Ni with B additions to promote/control wettability. The experimental data, obtained by sessile drop tests at 1130, 1200 and 1520 ∘C under carefully controlled conditions, are reported and discussed as a function of time, compositions and metal–ceramic micro-structure. In order to provide a basis for the correct interpretation of the experimental results, the ternary sections of the Ni–Hf–B system computed by CALPHAD methods are compared, with a good agreement, with the behaviour of the liquid Ni(B) phase in contact with the solid boride. By this way, the complex phenomena occurring at high temperatures between the molten phase and the diboride ceramic substrate (dissolution, reaction, intergranular penetration) and the formation of new phases during the solidification process have found a sound theoretical explication. The evolution of contact angles with time (spreading kinetics), which reached in all cases a nearly complete wetting, has also been interpreted in terms of reaction–dissolution interfacial processes.