Nanoindentation studies on Superelastic Behaviour of Cu-based Shape Memory Alloys Processed via Different routes

Nanoindentation is an instrumented indentation technique and is often used to determine the hardness and elastic modulus of materials from load-displacement data from indentation. By using this technique, the strain recovery by superelastic effect of shape memory alloys can be studied by analysing the loading and unloading curves. Evidence for forward and reverse stress-induced martensitic transformation in Ni-Ti SMAs has been obtained from load-displacement curves. In the present investigation, the superelastic recovery of Cu-Al-Mn and Cu-Al-Ni Shape memory alloys has been studied using Hysitron TI 950 nanoindenter with a Berkovich tip. The alloys were prepared from pure Cu (99.9 wt %), Al (99.9 wt %) , Ni(99.99 wt %) and Mn (99.8 wt %) by adopting different techniques: casting, conventional sintering and spark plasma sintering. The samples were heated upto 900 ^oC, held for 15 min and quenched in water.  A number of indentations were then made on the samples with loads ranging from 50 µN to 3000 µN. A trapezoidal loading profile (10s loading, 5s holding and 10s unloading) was used. The load-displacement curves at different loads were plotted and the subsequent recovery ratios for different composition were obtained and compared. The recovery ratios were calculated based on energy approach.