Interaction of HfB₂ with Nickel and Ni–20% Cr Alloy (Nichrome)

Interaction in the Ni–HfB₂ and NiCr–HfB₂ systems is studied. No new reaction products are found to form in the system with pure nickel in solid-phase interaction up to the contact melting point. Solidphase interaction in the NiCr–HfB₂ system resulting from the interdiffusion of boron from hafnium diboride and chromium from nichrome leads to a Cr₂B layer in the contact area. Contact melting begins at 1370 ± 10°C in the Ni–HfB₂ system and at 1450 ± 10°C in the NiCr–HfB₂ system. The starting metals and Hf₃Ni₂₀B₆ and Ni₃Hf phases, including the Cr₂Ni₃B6 phase in the NiCr–HfB₂ system, are basic products of the liquid-phase interaction in the hypoeutectic region of the phase diagrams of both systems. In the hypereutectic region of the phase diagrams, the metal component disappears and unreacted HfB2 appears additionally in the NiCr–HfB₂ system. Both systems are eutectic and have eutectic melting points of 1370 ± 10°C for Ni–HfB₂ and 1450 ± 10°C for NiCr–HfB₂ at 20 ± 2% HfB₂ in their quasibinary phase diagrams. Therefore, nickel and nichrome can be used to activate sintering since they act as a vanishing liquid phase. On the other hand, hightemperature oxidation-resistant hafnium diboride products can successfully perform in contact with nickel and nichrome products in the temperature range up to 1200°C.