The microstructural development following heat treatments of several rapidly-solidified Ni3Al-Cr and Ni3Al-Cr-B alloys was presented. Depending upon composition, the as-solidified samples were either 100% γ' phase-in the form of fine antiphase domains, or a mixture of γ' antiphase domains and β phases. Upon annealing, the as-solidified microstructures transformed to either antiphase domain-free γ' or mixtures of γ and γ' phases. For those compositions where the quenched microstructures were 100% γ' it was observed that antiphase domain coarsening followed conventional grain-growth kinetics, but when γ phase precipitated on the antiphase domain boundaries the rate constant changed abruptly while the time exponent remained unaffected. It was also found that alloys containing critical amounts of chromium and boron were susceptible to precipitation of the boride Cr5B3.

Microstructural Observations in Rapidly-Solidified and Heat-Treated Ni3Al-Cr Alloys. Carro, G., Flanagan, W.F.: Acta Metallurgica et Materialia, 1992, 40[8], 1809-17