Influence of strongly textured microstructure on the all-round shape memory effect of rapidly solidified Ni51Ti49 alloy

Abstract

Ni51Ti49 alloy strip with all-round shape memory effect (ARSME) was obtained through rapid solidification followed by constraint-aging treatment. The high cooling rate and large temperature gradient along the thickness direction of Ni51Ti49 alloy strip yield fine columnar grains and strong fiber texture of <100>B2 during rapid solidification. Such fine-grained and strongly textured microstructure increases the nucleation, limits the orientation and restricts the growth of Ni4Ti3 precipitates during constraint-aging treatment. The fine and well-aligned Ni4Ti3 precipitates with dispersive distribution introduce strong coherent stress field and numerous interfaces between the matrix and precipitates in the rapidly solidified and constraint-aged Ni51Ti49 alloy. Homogeneous composition and massive interfaces in the B2 matrix promote the simultaneity of local phase transformations. The strong coherent stress field and the excellent deformability of <100>B2-oriented grains contribute to large deformation and high recovery ratio of the alloy during phase transformation. Thus, the strongly textured microstructure formed during rapid solidification allows the constraint-aged NiTi alloy to possess superior ARSME with narrow phase transformation temperature range.