Discontinuous precipitation of Co₃V in a complex Co-based alloy

Abstract

Discontinuous precipitation of chromium-rich Co₃V lamellae has been found in a Co-based alloy containing 2 wt% V after prolonged ageing at 800 {\degr}C. This discontinuous precipitation is associated with a noticeable redistribution of alloying elements in the alloy relative to those parts of the aged alloy that preserve the c.c.p.-L1₂ microstructure found in the as-cast and homogenized condition. The orientation relationship between the c.c.p. Co-rich matrix and these hexagonal phase chromium-rich Co₃V precipitates is shown to be || and [1 1 1]_Co || , i.e. || and [1 1 1]_Co || in the four-index notation. 3 × 3 transformation matrices relating directions and planes in the two phases have been established. The observed orientation relationship between the two phases is consistent with low lattice misfit between the two phases.

Keywords:

• ageing
• cobalt
• crystallography
• precipitation
• transmission electron microscopy (TEM)

Acknowledgements

The authors are grateful to Dr J.P. Minshull for the alloy fabrication, homogenization and ageing work.