Martensitic transformations in β Ag-cd alloys

Abstract

Phase transformations have been studied inβ Ag-Cd alloys lying in the composition range 42.3 to 50.9 at. pct Cd. Thermal martensite with an orthorhombic structure was obtained on cooling below room temperature. The Ms temperature was found to change from —44° to — 137°C as the cadmium content changed from 44.2 at. pct Cd to 47.0 at. pct Cd. The martensite had a habit plane close to (133)β in good agreement with that calculated from the phenomenological theory assuming a (011) [0•11]β lattice-invariant shear. An fct martensite was obtained on moderate degrees of deformation at room temperature. This had a habit plane close to (110)β, again in good agreement with the phenomenological theory assuming a (110)[1•10]β lattice-invariant shear. On severe deformation a close-packed structure was obtained, this being fcc up to 45.5 at. pct Cd, hcp above 47.7 at. pct Cd, and a mixture of both fcc and hcp at 46.0 at. pct Cd. A spontaneous martensite with an fcc structure was found to occur along the thin edges of perforated specimens used for electron microscopy. A mechanism suggesting the course of the transformation has been proposed.