Synchrotron Radiation X-ray Diffraction Measurements of the Thermal Response of a Processing-Induced NiTi Strain Glass Alloy

Shape memory alloys (SMAs) show great potential across many fields and various applications with their unique shape memory abilities. These abilities stem from a solid-state martensite transformation, where this martensite phase acts as a long-range ordering of lattice strain. Strain glass alloys (SGAs) originate from SMAs in which the long-range martensitic transformation is replaced with a strain glass transition. These SGAs originate from inducing a sufficient amount of lattice distortion into a SMA system to frustrate the quintessential martensitic transformation enough to generate a strain glass transition. This results in a structure of a distorted crystalline matrix with nano domains of glassy martensite. In this study, we compare the transformation behavior of a martensitic NiTi SMA with a processing-induced NiTi SGA during thermal cycling using wide-angle synchrotron radiation X-ray diffraction (WAXS). Based on the thermal cycling results, three observations about processing-induced SGAs as compared to SMAs can be seen: (1) retention of distorted austenite at high and low temperatures, (2) broadening of diffraction peaks in WAXS and disappearance of the thermal peaks in DSC measurements both due to induced strain, and (3) gradual increase in the amount of the martensitic phase.