Large elastic strains and ductile necking of W nanowires embedded in TiNi matrix

The deformation behaviors of W nanowires embedded in a TiNi matrix were investigated by means of in-situ synchrotron high energy X-ray diffraction (HEXRD) and in-situ transmission electron microscopy (TEM) analysis during tensile deformation. The HEXRD measurement indicated that the W nanowires exhibited an average lattice strain of about 1.50 %, whereas the TEM examination revealed a local elastic strain of about 4.59 % in areas adjacent to the TiNi matrix where stress-induced martensitic transformation occurred. This strain corresponds to a stress of ∼15 GPa for the W nanowires. In addition, in areas adjacent to the TiNi matrix where plastic deformation and cracking were generated, the W nanowire showed significant ductile necking with ∼80 % reduction in cross-section area. The ductile necking of W nanowire is attributed to the lack of protection from the stress-induced martensitic transformation of the TiNi matrix.