Microstructures of L21/L12 multi-phase intermetallics in Co-Ni-Al-Ti system

On the basis of the two ternary systems of Co-Al-Ti and Ni-Al-Ti, a series of high-temperature structural intermetallic alloys comprised of L2(1)-type (Co, Ni)(2)AlTi and Ll(2)-type (Co, Ni)(3)(Al, Ti) ordered phases in the Co-Ni-Al-Ti quaternary system were designed and melted to take the advantages of both the high elevated temperature strength of the L2(1) phase and the intrinsic room temperature ductility of the L1(2) phase. Analysis of the phase equilibrium, phase structure and microstructures of the as-cast and heat-treated alloys were conducted to gain some clues for the further optimization of the compositions, microstructures and processing.