Intermetallic phase formation during combustion synthesis of mechanically activated Ni-Ti alloy

Intermetallic phase formation and oxidation reaction during combustion synthesis (CS) of Ni-Ti equiatomic mixture are affected by mechanical activation (MA) and pre-heating conditions. Important parameters are ignition time, reaction duration, temperature rise, microstructural change, titanium oxidation and intermetallic phase formation. Superelasticity and shape memory effects are influenced by two-stage austenite-rhombohedral and rhombohedral-martensite transformations detected by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) of the combusted samples. Tension tests indicated superelastic behavior after ۱ h, production of Ni۳Ti after ½ h and delayed superelastic/thermoelastic behavior after ۲ h MA. Results indicate that pre-combustion heating fosters mono-phase formation and titanium oxidation; while mechanical activation lowers ignition-start-time, synthesis-duration and Ni۳Ti formation.