Effect of annealing temperature on the microstructure of rapidly-solidified TiNi-Cu alloy ribbons

Ti53.5Ni22.8Cu23.7 shape memory alloy ribbons have been fabricated by rapid solidification and then the effect of annealing temperature on their microstructures was investigated.The microstructure is very sensitive to the annealing temperature.The plate precipitates with width of 10 to 15nm has coherent relationship with the matrix when annealed at 450℃.When annealed at 500℃,the microstructure is coexistence of nanocrystalline B19 and single-crystalline B19.Ti2(Ni+Cu) precipitates were formed when annealing temperature is higher than 550℃.The width of plate Ti2(Ni+Cu) precipitates increases from 30 to 50nm to 200 to 300nm with increasing annealing temperature.When annealed at 650℃,the martensite morphology was influenced by the distributions of Ti2(Ni+Cu) precipitates and moire fringe can locally be formed due to high density of over lapping irregular structured grain boundaries.