Borides of M5B3 type in heat-resistant nickel alloys with ∼ 5 and 15-20 mass. % of chromium

Transmission electron microscopy was applied for morphological and crystallographic studies of M5B3 borides in heat resisting nickel base alloys containing 5 wt. % Cr and 10-12 wt. % W or 15-20 wt. % Cr and 3-5 wt. % W. Variety of morphologies were described for borides as well as orientational relation of borides to (γ+γ')-matrix. Investigations were conducted to reveal the effects of segregation, phase and structure heterogeneities on boride distribution over the alloy volume. The results obtained testified to the fact that boride formation was one of the main phase transformations in boron alloyed heat resisting nickel alloys. This conclusion is important as operational temperatures of the alloys considered coincide with the temperature of boride precipitation out of solid solution