Spinodal decomposition of a nickel-titanium alloy

The decomposition of a supersaturated nickel-14% titanium solid solution has been investigated by field-ion microscopy. It was established that the formation of ordered γ′ (Ni3Ti) precipitates proceeded via a spinodal mechanism and that no distinct precipitate (e.g. Ni6Ti) was involved. The diffuse nature of the interface between ordered and disordered regions was clearly illustrated by a new technique for determining composition fluctuations over short distances. Considerable sharpening of the interface occurred on isothermal ageing. The spinodal temperature was estimated to be (880 ± 70) °C for this composition and a value of (0.6 ± 0.1) nm was obtained for the interaction parameter, Ψ.