Microstructural effects of strain aging on NiTi pseudoelastic wires by synchrotron X-ray micro-diffraction

Abstract

In this work, we explore the consequences of strain aging pseudoelastic NiTi wires (2.46 mm diameter) at moderate temperatures (100°C). The changes of the stress-strain behaviour on aged, as compared with non-aged wires, with comparatively smaller changes in thermal transformation, indicate the existence of relevant strain fields on these wires. The fact that thinner wires perform differently on aging suggests the possibility of radial dependence of the strain fields. Measurements were performed at CELLS-ALBA synchrotron, BL04 Materials Science Powder Diffraction beam-line. X-ray micro-diffraction for near 10 (μm)2 (FWHM) zones on cross-sections of samples was done, aiming to detect residual strains as function of radial position on the wire. The results show very small changes of diffraction peaks position, with more relevant variations near the surface. This might be interpreted as a high sensitivity of the transformation on stresses enabling defined paths of transformation.