The role of α- to ɛ-Co phase transformation on strain hardening of a Co–Cr–Mo laser clad

A laser clad Co–Cr–Mo alloy has been analysed by the electron backscatter diffraction (EBSD) technique to examine the microstructural evolution during tensile deformation and to study the role of the evolved microstructure on strain hardening of the clad. The allotropic phase transformation from α- to ɛ-Co, that did not take place during cooling from the solidification temperature, occurs in the form of a strain-induced transformation during plastic deformation. Combined slip on non-parallel planes in parallel bands of α- and ɛ-Co prevents the formation of cracks and contributes to the strain hardening of the material. Due to twin formation at intersecting ɛ-Co bands, { 1   1 ¯   0   1 } planes become almost parallel to {1 1 1} planes of α-Co, and facilitate further glide of dislocations. Owing to the strain-induced transformation of α- to ɛ-Co, the laser clad Co–Cr–Mo investigated in this study can accommodate high deformation before cracks are formed at the “wavy slip-lines” and the precipitates.