Microstructure and transformation temperatures in rapid solidified Ni-Ti alloys. Part II: The effect of copper addition

摘要

Ternary rapidly solidified alloys were produced and tested in this research work. Cu was added to a near equiatomic Ti_(49)Ni_(51) alloy, by substituting Ni. Three compositions were considered: Ti_(49)Ni_(51-x)Cu_x (x = 5, 15, 25). Samples with the shape of cones were obtained, in order to test the effects of different rapid solidification rates. The aim of this research is to analyze the use of rapid solidification in the low regime of cooling rates (10~2-10~3 K/s), which is much more suitable for industrial processes than the extremely high cooling rates (such as melt spinning). We found that, as Cu was added into the alloy, the transformation temperatures rapidly decline and they reach a minimum between 5 and 15 at.% of Cu. Then, they begin to increase and they are comparable with those of the binary alloy when Cu is equal to 25 at.% A higher cooling rate lowers the transformation temperatures, showing an opposite effect respect to Cu addition. Moreover, the Cu addition reduces the transformation hysteresis. Some precipitates were found in the ternary alloys and Ni and Cu showed a linear exchanging tendency in the precipitates, in the explored range of Cu content.