Effect of hot Rolling on Transformation Behavior of NiTiHf high temperature Shape Memory Alloy

Transformation behavior of hot rolled Ni₅₀Ti₄₀Hf₁₀ alloy was studied using differential scanning calorimeter (DSC) with the aim of revealing effects of thickness reduction on hardness and transformation temperatures of hot rolled plates. Hot rolled specimens showed one-stage martensite transformation of B₂ B₁₉¢. With increasing thickness reduction, transformation temperatures decreased, and transformation peaks were broadened intensively due to increasing dislocation density and blockage effect of dislocation on transformation. Temperatures of the transformation were conversely proportional to hardness of the hot rolled specimens. Strengthening effect of hot rolling on Ms temperature was found to follow this equation: M_s = T₀ - KDHv. K value for hot rolled Ni₅₀Ti₄₀Hf₁₀ alloy was found to be 0.404 °C Hv^-1.