Decomposition of dilute NiTi alloys studied by high resolution X-ray diffractometry

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High-resolution and high-sensitivity wide-angle X-ray diffractometry was used to study the decomposition of nickel-rich NiTi single crytals. The position of the fundamental 220 reflections and the satellites flanking them along the 〈100〉 directions were investigated after heat treatment for different periods of time at 600 and, subsequently, at 700 °C. The satellites indicated periodic strain modulations caused by compositional modulations. The position of the fundamental reflections remained constant while the satellites revealed a characteristic four-fold symmetry. This may be considered evidence for a single-phase, locally stressed state, as expected for a spinodal decomposition mechanism.