The role of the martensite transformation for the mechanical amorphisation of NiTi

Physical metallurgy of Ti–Ni-based shape memory alloys

“…Koike et al [293,294] found that crystal-amorphous transformation occurs in Ti-50.8Ni alloy by cold-rolling at room temperature by as large as 60% reduction. This was also confirmed by Ewert et al [295] and Nakayama et al [296] later. One typical example is shown in Fig.…”

“…Ewert et al [295] studied the amorphisation of Ti-50Ni (TiNi-I) and Ti-50.2Ni-0.6Cu (TiNi-II) alloys by changing strains widely, but obtained amorphous fraction of 30% at maximum at the true strain of 2.0, which corresponds to 86% reduction in the usual expression, as shown in Fig. 74.…”

Structure and Properties of the Ti–50.0 at%Ni Alloy after Strain Hardening and Nanocrystallizing Thermomechanical Processing

“…These results correlate with known data on B2-phase stabilization after severe deformation of Ti-Ni alloys. 6,[18][19][20][21][22] The amorphous volume fraction of %50% evaluated from TEM foils is much higher than 10% measured by Ewert et al 23) by DSC and TEM techniques in similar conditions (cold-rolling of Ti-50 at%Ni alloy at a true strain of e ¼ 2). In our opinion, the presence of only 10% of amorphous material cannot justify principal differences in the material properties between low and severe levels of cold-work, as it will be illustrated further.…”

Blast Coating of Superelastic NiTi Wire with PTFE to Enhance Wear Properties

“…Severe plastic deformation of NiTi has been investigated using various methods such as shot peening, high pressure torsion, cold-rolling, equal angular extrusion and laser shot peening, resulting in the formation of deformation-induced martensite (DIM) and amorphization [21][22][23][24][25][26]. The formation of DIM is associated with highly dense twinning and gives rise a work hardened layer and compressive residual stress that may enhance fatigue performance [25,27].…”