Structural Changes in Cobalt Solid-Solution Crystals Due to Milling

Abstract A detailed microstructural study was carried out using a field emission-scanning electron microscope with the aim of analysing the effect of surface work-hardening which occurs when milling the cobalt based hard facing alloy ”Stellite 12“. The strengthening was determined to be caused by the formation of two-dimensional structural defects in the cobalt solid-solution matrix. The assumption that a stress induced martensitic transformation of the crystalline areas of the cubic cobalt phase into thin hexagonal cobalt platelets occurs was confirmed by X-ray diffraction phase analysis. In addition, it was assumed that stacking faults would be formed. For the microscopic investigation, the channeling effect achieved by imaging using a conventional ring-shaped back scattered electron detector proved most useful. Because of needed high quality of polished sections, an optimised method of preparation was developed.