Variation in kinetics of martensitic transformation during partial thermal cycling of the TiNi alloy

• Partial forward transition cycling induces the damage in whole alloy volume.
• Partial reverse transition cycling induces the damage in “transforming” volumes.
• Partial reverse transition cycling does not induce the damage in “martensite” volumes.
• Internal stresses relax by plastic strain in the austenite phase.
• Internal stresses relax by reorientation of martensite crystals in martensite phase.

A method of differential scanning calorimetry has been used for the study of variation in the kinetics of thermal elastic martensitic transformation during the thermal cycling of the equiatomic TiNi alloy through the different fractions of forward or reverse martensitic transformation temperature ranges. The results of the study have shown that “partial cooling” cycling results in damage to the crystalline structure in “transforming” and “austenite” volumes independently of whether or not “austenite” volumes undergo martensitic transformation during partial cycling. The structure damage in “martensite” volumes does not occur during “partial heating” cycling. It is caused by the fact that internal stresses relax through plastic strain in the austenite phase, resulting in an increase in defect density or the reorientation of martensite crystals in the martensite phase without the accumulation of defects.