In-situ high energy X-ray diffraction study of deformation behavior in Nb nanoparticle-martensitic NiTi composite wire

This study investigated the deformation behavior in Nb nanoparticle-martensitic NiTi composite wire during tensile loading by means of in-situ high-energy X-ray diffraction. Compared to Nb nanowires, the dispersedly distributed Nb nanoparticles have little effect on the transformation and deformation behaviors of NiTi matrix, causing the absence of R phase transformation and the occurrence of deformation twinning in NiTi matrix. Meanwhile, the occurrence of deformation twinning in NiTi matrix can reduce the shape strain to be coordinated by the unfavorable orientated martensite variants, and thus decreases the internal stress among NiTi martensite variants generated during martensite reorientation process. In addition, TEM result proved that Nb nanoparticles can achieve exceptionally large elastic strain in B19′-NiTi matrix (∼4%), just as Nb nanowires. However, this large elastic strain (stress) will be released with the occurrence of NiTi deformation twinning.