Effect of titanium on structure and martensic transformation in rapidly solidified Cu–Al–Ni–Mn–Ti alloys

Abstract

Alloys of composition Cu–(11.8–13.5)%Al–(3.2–4)%Ni–(2–3)%Mn and 0–1%Ti (wt.%) were cast using the melt spinning method in He atmosphere. Ribbons obtained in this process showed grains from 0.5 to 30 μm depending on the type of alloy and wheel speed. Bulk alloys and most of the ribbons contained mixed 18R and 2H type martensite at room temperature (RT). Some ribbons, crystallizing at the highest cooling rate, retained also β phase due to a drop of Ms below RT. The Ms temperatures in ribbons were strongly lowered with increasing wheel speed controlling the solidification rate. This drop of Ms shows a linear relationship with d−1/2, where d is grain size. The strongest decrease of Ms and smallest grains were found in the ribbons containing titanium due to its grain refinement effect. The cubic Ti rich precipitates, present in both Cu–Al–Ni–Ti and Cu–Al–Ni–Mn–Ti bulk, were dispersed in ribbons cast with intermediate cooling rates of up to 26 m s−1, but suppressed for higher cooling rates. The transformation hysteresis loop was much broader in ribbons due to presence of coherent Ti rich precipitates and differences in grain size which is particularly important in the ultra small grain size range.