© EDP Sciences, Les Ulis Effects of Si and Nb additions on CuAINiTi rapidily solidified alloys microstructures

Abstract Intensive investigations have been carried out on CuAINiTi shape memory alloys (SMAs) with lwt.%Ti and Ni content from 5 to 6 wt%. In this present work, we used a rapid solidification technique to prepare alloys of two compositions: (wt%) Cu^Al^^T^Si, , CuMAli3Ni5Ti,Nb2. The ribbons obtained were characterised by means of XRD, DSC measurements and TEM observations. XRD patterns indicated that the first alloy has a two-phase structure with beta and martensite 18R phases, whereas the second one is only beta. DSC measurements gave characteristic transformations temperatures. The Si-containing alloy showed low temperature transformations with Ms about-88°C and Af at-41°C in as-quenched state. The Nb-containing alloy exhibited high temperature transformations with Af about 170°C in the as-quenched state, which is quite higher for this alloy family. The transformation temperatures are stabilised after only one cycle at ATM=(M,-Mf) constant for both alloys. This stabilisation is likely to be generated, in the case of Cuy^Al^NijT^Nbj, by nanocrystalline precipitates revealed on TEM micrographs. Narrow and faulted martensite plates have been observed in agreement with previous results on rapidly solidified CuAINiTi SMAs. CuAl single crystal SMA alloys have good shape memory effect (SME) whereas the polycrystalline alloys exhibit poor mechanical properties such embrittlement. Since they are attractive for SM