Microstructure of Ni-48 at.%Ti Alloy Prepared from Powder and by Conventional Metallurgy

Microstructure of the samples of the alloy Ni-48 at.%Ti prepared from elemental powders by self-propagating high-temperature synthesis is compared to that of the same alloy cast by conventional vacuum induction melting from bulk metals. Scanning and transmission electron microscopy observations show differences in the phase structure. Besides NiTi matrix, both materials contain also NiTi2, Ni2Ti, Ni3Ti2, Ni3Ti, and Ni4Ti3 phases. Slow furnace cooling after long term annealing at 1000 degrees C leads to the transformation of the Ni4Ti3 phase into the Ni8Ti5 phase in the self-propagating high-temperature synthesis material. In the conventionally cast alloy, the Ni8Ti5 phase was not found.