The Effect Of Alloy Formulation, Cold Work and Inclusion Content On Micro-Void Formation In NiTi Alloys

Inclusion and micro-void content are important for the performance of high performance devices made from nickel-titanium alloys.  This is particularly important for fatigue life. Hot rolled NiTi alloy bars formulated for As = -50, -25, -15, 0, +30, +55, +70 and +95C are cold drawn to reductions from 5% to 50%.  Area fraction of voids is correlated to % cold work, area % of carbides and area % of oxides starting from the hot rolled bars.  Area fraction of oxides increases with As.  There is a small increase from As = -50oC to As = +30oC and a bigger increase from As = +55oC to As = +95oC. Micro-void formation increases with the amount of cold work in all alloys. The effect of inclusion content and inclusion species will be correlated to the amount of micro-void formation. The implications for the optimization of alloy formulation for microstructure and performance will be discussed.