Microstructures and mechanical properties of CoTi(B2)-Co2TiAl(L21) pseudo-binary intermetallic compounds

Continuous ordering from the B2 phase to the L21 phase in the CoTi–Co2TiAl psuedo-binary intermetallic compounds was investigated, using X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM observation showed that antiphase domain structures were developed, accompanied with the B2/L21 continuous ordering, and their morphology and size depended on alloy composition, annealing temperature and time. Room-temperature hardening occurred by isothermal annealing at 1073 K and 1173 K, and was attributed to the development of the antiphase domain structure and the increase in the long-range ordering parameter of the L21 phase. Also, high temperature strength in the CoTi–Co2TiAl psuedo-binary intermetallic compounds was evaluated by compression test over a wide range of temperature, and understood, on the basis of solid solution strengthening and additionally antiphase domain strengthening.