Effect of Heat Treatment on Microstructure and Mechanical Properties of Selective-Laser-Melted CoCrMoW
CoCrMoW alloy is an ideal material for metal substructures in porcelain-fused-to-metal crowns and removable partial dentures.This study focuses on the heat treatment process of selective-laser-melted CoCrMoW alloy,particularly addressing issues such as low production efficiency due to prolonged aging time,as well as part dimension consistency and warping after heat treatment.In this study,specimens were printed using 15-53 μm gas-atomized powder as raw material,and were subjected to heat treatment at temperatures of 920,960,1 000℃for 1 hour,followed by furnace cooling to 600℃before removal.The effects of heat treatment on the microstructure and mechanical properties were investigated using metallographic microscopy,SEM,EDS,tensile testing.It was found that after heat treatment,the second phase precipitated in both the intra-granular and inter-granular regions of the alloy matrix.After heat treatment at 920℃and 960℃,the precipitates were uniformly distributed and dense,while after heat treatment at 1 000℃,the precipitates within the grains had partially dissolved.Furthermore,the size of the precipitates noticeably increased with increasing heat treatment temperature.Based on EDS compositional analysis,the precipitates was identified as possibly the intermetallic compound Co3(Mo,W)2Si.Under different heat treatment conditions,the mechanical properties of the samples differed significantly,closely related to the distribution,quantity,and size of the precipitates.The dense and fine precipitates at 920℃showed the most significant strengthening effect on the matrix,resulting in the highest yield strength(1 134 MPa),lowest plasticity(7%elongation),and quasi-cleavage fracture with brittle tendency.As the precipitates coarsened and partially dissolved,the strength gradually decreased while the plasticity increased.At 1 000℃,the mechanical properties were restored to levels close to the as-built state,with a yield strength of 892 MPa,elongation of 14.8%,and quasi-cleavage fracture with ductile tendency,demonstrating both high strength and high plasticity.Additionally,heat treatment at higher temperatures can reduce residual stress and warping deformation more effectively,with the smallest deformation(0.13 mm)observed in specimens treated at 1 000℃.The choice of heat treatment conditions depends on the requirements of different applications and is crucial for controlling the performance and deformation of selective-laser-melted CoCrMoW alloy.
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