Effects of thermal treatments on microstructure and mechanical properties of a Co-Cr-Mo-W biomedical alloy produced, by laser sintering

Direct Metal Laser Sintering (DMLS) technology based on a layer by layer production process was used to produce a Co-Cr-Mo-W alloy specifically developed for biomedical applications. The alloy mechanical response and microstructure were investigated in the as-sintered state and after post-production thermal treatments. Roughness and hardness measurements, and tensile and flexural tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and Microanalysis (EDX) were used to investigate the microstructure in different conditions. Results showed an intricate network of epsilon-Co (hcp) lamellae in the gamma-Co (fcc) matrix responsible of the high UTS and hardness values in the as-sintered state. Thermal treatments increase volume fraction of the epsilon-Co (hcp) martensite but slightly modify the average size of the lamellar structure. Nevertheless, thermal treatments are capable of producing a sensible increase in UTS and hardness and a strong reduction in ductility. These latter effects were mainly attributed to the massive precipitation of an hcp Co-3(Mo,W)(2)Si phase and the contemporary formation of Si-rich inclusions. (C) 2016 Elsevier Ltd. All rights reserved.