The effect of rapidly solidified microstructures on martensitic transformation behaviours in Ti50Ni30Cu20 alloys

Ti50Ni30Cu20 (at.%) alloy ribbons have been fabricated by melt spinning and then their microstructures and shape memory characteristics were investigated by means of X-ray diffraction optical and transmission electron microscopies and differential scanning calorimetry. In these experiments particular attention has been paid to change the velocity of cooling wheel from 33 m/s to 55 m/s to control the thickness of ribbons. Microstructural analysis of melt-spun ribbons showed that the proportion of amorphous solidification at the chilled side of the ribbon increased with wheel. The perfect amorphous ribbon was produced in Ti50Ni30Cu20 alloy when the ribbon was fabricated at the wheel velocity of 55 m/s and the melt spinning temperature of 1500 °C. After annealing the amorphous ribbons at 440 °C for 10 min, they were crystallized with fine grains of B19 phase. The effect of these microstructural changes on martensitic transformation behaviours is discussed.