Kink Formation and Strengthening Effects in TiNi–V Eutectic Alloys with Mille-Feuille Structure

Abstract

Kink formation by rolling and its strengthening effects on the mechanical properties of TiNi–V alloy were investigated. The as-cast TiNi–V alloy had a eutectic lamellar structure consisting of B2-TiNi and bcc-V phases. When the alloy was rolled, kinks were formed in the layered structure. The Vickers hardness of the alloy increased after it was subjected to 30% rolling reduction, and then decreased with increasing annealing temperature. After the rolled alloy was annealed at 973 K, its hardness recovered to the original value; however, the layer structure and kinks remained in the alloy. Thus, both dislocations and kinks were introduced into the alloy by rolling, but only dislocations disappeared upon annealing. Therefore, a layered TiNi–V alloy with only kinks but no dislocations was obtained. A comparison of the yield stresses of as-cast, 30% rolled, and annealed alloy specimens revealed that the magnitude of strengthening by dislocations and kinks was about 170 and 40 MPa, respectively. Therefore, kink formation and kink strengthening effects similar to those observed in Mg-based long-period stacking ordered (LPSO) alloys were observed.

Fig. 6 Stress-strain curves for (a) as-cast, (b) 30% rolled and (c) 30% rolled and annealed (973 K) B2+bcc two-phase Ti₃₅Ni_39.5V_25.5 alloys (d) B2-TiNi single-phase Ti₄₉Ni₄₇V₄ alloy and (e) bcc-V single-phase Ti₈Ni₆V₈₆ alloy.