Phase transformation in platinum-iron-copper Ternary system

Abstract

The presence of a distinct compound in the Pt-Fe Cu system at Pt FeCu composition was hypothesised by Nemilov in 1944, but tre compound (Tulameenite) was first identified by Cabri et al in natural alloys from the platinum placer deposits of the Tulameen river in British Columbia. The present research was initiated to determine the Pt-Fe-Cu phase diagram in the Pt FeCu region and thus to determine the composition range of Tulameenite and its compositional and structural changes during different thermal treatments using synthetic material. Primary investigations have revealed that the compound is a single phase disordered f.c.c. solid-solution above 1178°c. On quenching, it transforms, probably by a martensitic transformation, to an ordered tetragonal structure. Multiple twinning on {101} habit planes avoids any macroscopic shape change due to the ordering. The twinned structure is unstable, and thermal treatments produce stress-relief recrystallization accompanied by deformation twins and grain-boundary fractures as further stress-relief mechanisms. Tulameenite forms an extensive single phase region of solid- solution continuous with the binary region based on the compound FePt. At lower temperatures the stoichiometric compound Pt2 FeCu enters a two-phase field comprising a non­- stoichiometric compound together with an ordered cubic phase. The transformation to this two-phase structure occurs by different precipitation mechanisms which are accompanied by recrystallization of the matrlx in some cases.