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

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 obtai ned in this process showed grains from 0.5 to 30 mu m depending on the type of alloy and wheel speed. Bulk alloys and most of the ribbons contained mi xed 18R and 2H type martensite at room temperature (RT). Some ribbons, crys tallizing at the highest cooling rate, retained also beta phase due to a dr op of M-s below RT. The M-s temperatures in ribbons were strongly lowered w ith increasing wheel speed controlling the solidification rate. This drop o f M-s shows a linear relationship with d(-1/2), where d is grain size. The strongest decrease of M-s and smallest grains were found in the ribbons con taining titanium due to its grain refinement effect. The cubic Ti rich prec ipitates, present in both Cu-Al-Ni-Ti and Cu-Al-Ni-Mn-Ti bulk, were dispers ed in ribbons cast with intermediate cooling rates of up to 26 m s(-1), but suppressed for higher cooling rates. The transformation hysteresis loop wa s 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. (C) 1999 Published by Elsevier Science S.A. All rig hts reserved.