Microstructure of NiTi shape memory alloy due to tension–compression cyclic deformation

The microstructure and linear superelasticity of cold-drawn TiNi alloy

“…In the thermal Total number 4 ---3 1 5 2 7 3 1 -25 -8 29 23 12 4 5 --32 14 16 8 10 2 -34 12 13 2 6 -22 33 13 10 30 4 3 7 3 7 martensite, the (111( ) Type I twin was mainly believed to be a deformation twin or a variant accommodation twin [5], which implies that it could accommodate the external stress field more easily, especially the shear strains between martensite variants. A recent study [14] on the TiNi alloy due to tension-compression cyclic deformation showed that the (111( ) Type I twin was more frequently observed in the cycled samples. This may be due to the fact that the value of the twinning shear for the (111( ) Type I twin, 0.3096, is the largest for all the twinning systems observed so far in the B19% martensite [4], as suggested by Xie et al [14].…”

“…A recent study [14] on the TiNi alloy due to tension-compression cyclic deformation showed that the (111( ) Type I twin was more frequently observed in the cycled samples. This may be due to the fact that the value of the twinning shear for the (111( ) Type I twin, 0.3096, is the largest for all the twinning systems observed so far in the B19% martensite [4], as suggested by Xie et al [14]. A similar situation had also been reported in the TiNiNb alloy, that the (111( ) Type I twin was preferentially formed during the stress-induced martensitic transformation [15].…”

“…Recently, it was found in the TiNi alloy due to tension -compression cycle deformation [14] and the stress-induced martensite in TiNiNb 2. When the area reduction is higher than 16%, the adjustment and development of the internal twinnings inside individual martensite variant becomes the dominant deformation mode.…”

“…The ingot was hot swaged and rolled at 850°C to rods with approximately 8 mm diameter. After annealing at 850°C for 1 h, some specimens were colddrawn at room temperature to the extents of 5,8,12,14,16,22 and 30% reduction in area, respectively. The tensile tests were carried out on an Instron-1186 testing machine with a strain rate of 4.1 × 10 − 4 s − 1 .…”

Influence of Dynamic Compression on Phase Transformation of Martensitic NiTi Shape Memory Alloys

“…There is no twin relation between neighboring martensite variants after compression because of the generation and movement of lattice defects. [43][44][45][46] The mechanical behaviors are nearly the same before the plastic deformation of reoriented martensite under quasi-static compression and dynamic compression, and the plastic stress level under dynamic loading is 500 MPa higher than that under quasi-static compression. [47] NiTi SMAs also exhibit a dynamic sensitivity.…”