The effects of grain size on the phase transformation properties of annealed (Ti/Ni/W) shape memory alloy multilayers

(Ti/Ni/W)n multilayer films were annealed to form a two-phase (B2-TiNi and β-W) system. Grain sizes extracted from X-ray diffraction profiles of annealed films revealed that B2-TiNi decreases with increasing W, due to the immiscible W layers obstructing its grain growth. With decreasing B2-TiNi grain size the Rs (B2–R) transformation temperature is not affected but the Ms (R–B19′) transformation temperature decreases significantly. Thus the addition of W to Ti–Ni is effective to induce the B2–R single-step transformation due to grain size effects.

Research highlights► Annealed Ti/Ni/W multilayer films forms two-phase B2-TiNi and β-W system. ► Grain size of B2-TiNi decreases with increasing W amount. ► Grain size effects explains the separation of Ms and Rs temperatures. ► W alloying is effective to induce B2–R transformation.