Microstructure and mechanical properties of a rapidly solidified Ni3Al-Cr alloy after thermal treatments

The effect of thermal treatments at 750, 900 and 1000 degrees C on the microstructure and mechanical properties of a rapidly solidified Ni3Al-Cr ahoy is reported. The microstructure of the ribbons in the as-rapidly solidified (RS) condition consisted of a partially ordered Ni3Al matrix and a fine Cr-rich second phase located at cell and grain boundaries. New and coarser alpha-Cr particles precipitated after annealing at 750 degrees C. No significant changes in the microstructure were observed for longer times. The alpha-Cr precipitates tended to dissolve in the Ni3Al matrix after annealing at 900 and 1000 degrees C. This dissolution seems to be controlled by the lattice Cr-diffusion in Ni3Al since the volume fraction of alpha-Cr particles decreased with increasing time and/or temperature of thermal treatments. The mechanical properties of the ribbons were influenced by the microstructural changes such as grain size, volume fraction and size of the alpha-Cr precipitates, that occurred during the annealing treatments. Thus, ribbons in the RS condition and after annealing at 750 degrees C were brittle however, they exhibited ductile behaviour after thermal treatments at 900 and 1000 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved.