The Evolution Of Shape Memory Alloy Deformation Texture And Its Effect On The Recovery Strain

wide hysteresis shape memory alloy is used to produce coupling and fasteners for pipe connection due to its excellent properties of high vibrancy performance, reducing weight and easy installation and removal. It requires to precisely control material properties for better industry device performance. The formation of the deformation texture and recrystallization texture during Ni47Ti44Nb9alloy processing causes the anisotropy. Therefore a comprehensive study of the evolution of Ni47Ti44Nb9alloy deformation texture and its effect on recovery properties is necessary. In this paper, a systematic study is carried on the matrix texture of Ni47Ti44Nb9alloy ingot, plate and wire by using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM).Microstructure of Ni47Ti44Nb9ingot is composed by the dendritic NiTi matrix phase and the eutectic phase of the NiTi and β-Nb, and the Ni/Ti ratio of NiTi matrix is significantly higher than that of β-Nb. Ingot transverse section orientation is close to{114},{112},{332} and{110}.Deformation texture of cold rolled plate with the different reduction and rolled time is the y fibre texture (<111>//ND). It proves that the texture evolution is from{111}<112> to{111}<110> and the stable texture at medium deformation is{111}<110>. The orientation density of secondary cold rolled plate is greatly enhanced and major texture spreads from{111}<110> to{110}<110> in the α fibre (<110>//RD).The evolution of cold rolled texture of ingot transverse section sample with weak texture is{111}<112>→{111}<123>→{111}<110>.Textures of secondary cold rolled plates along0°,45°,90°to the rolling direction, are mainly the α fibre and y fibre texture with different strong position. The major texture of90°secondary cold rolled is (554)[110],(554)[225] and (556)[51710] and the overall texture intensity of y fibre is simultaneously enhanced. The texture of90°cold rolled has higher orientation density than that of0°,45°. The major texture for the plate forth cold rolled along90°to RD is {111}<110>.The recrystallization texture of Ni47Ti44Nb9alloy cold rolled plate is mainly composed by {111}<110> and {111}<112>. The evolution mechanism of annealed texture is proposed following the recrystallization grain preferred nucleation and preferred growth mechanism and strong {lll}<110> texture can promote the formation of {111}<112> recrystallization texture.From the plate center to the surface. Ni47Ti44Nb9alloy reveals gradually weakening texture orientation density with close texture type, so the texture at the0.85plate thickness location can represent the entire plate.Texture intensity is enhanced by increasing reduction, rolling along90°to rolling direction and annealing of rolled plate. Optimization rolled procedure of Ni47Ti44Nb9alloy is warm rolled by35～45%reduction at450℃with total70～90%deformation.The hot forged bar has <111> fibre texture, and <113> fibre texture is major texture in hot and cold drawn wire. The annealing texture of NiTi matrix phase of55%cold drawn wire is <112> fibre texture, while that of P-Nb is <110> fibre texture.The paper applies a mathematical model prososed by lattice distortion theory to calculate the recovery strain of polycrystalline Ni47Ti44Nb9alloy, and conducts a preliminary verification. Recovery strains variation with the angle to the RI) of theoretical calculations has the same regularity with that of experimental data. It can qualitatively predict recovery strain variation of different direction. Recovery strain variation with the angle to the RD of {111]<112>,{111}<11()> texture first increases and then decreases, and the wire with <112> fibre texture has higher recovery strain than the same orientation plate.