Effect of stress-relief anneal time on residual stress of Co-Cr-Mo parts manufactured with selective laser melting

Thermal inconsistencies inherent in the selective laser melting manufacturing process generate residual stress that may exceed the yield strength of the material resulting in deformation and cracking of components. This may however be mitigated through a stress-relief annealing process. The purpose of this study is to investigate the effect of stress-relief anneal time on the residual stress in selective laser melted Co-Cr-Mo components by means of simulation and neutron diffraction techniques. Thin-walled samples were manufactured and subjected to heat treatment at 1065°C for different holding times (0.25, 1, 2 and 3 hours) as well as a sample heat treated at 750°C for 1 hour. Evaluation of the residual stress reveals that the heat-treated samples have significantly lower residual stress as compared to an as-built (non-heat treated) control sample. Results indicate that the range of annealing times investigated produce near-identical residual stress values. Higher annealing temperatures however result in lower residual stresses. Comparison of simulated and neutron diffraction results indicate anisotropic behaviour of the material which can be attributed to the layer-wise addition of material.