Comparative analysis of the microstructures and mechanical properties of Co-Cr dental alloys fabricated by different methods

Statement of problem. Limited information is available regarding the microstructures and mechanical properties of Co-Cr dental alloys prepared using conventional casting (CAST), computer numerical control (CNC) milling, and selective laser melting (SLM). Purpose. The purpose of this in vitro study was to evaluate the mechanical properties and microstructures of Co-Cr dental alloys fabricated using conventional casting, computer numerical control milling, and selective laser melting and to estimate the potential of applying the SLM technique in prosthetic dentistry. Materials and Methods. Each group (n=6) of 50-mm-long Co-Cr alloy, dumbbell-shaped specimens was fabricated using the CAST, CNC, and SLM techniques. For each technique, the corresponding commercial alloy material was used. The mechanical properties were evaluated using a tensile test according to International Organization for Standardization (ISO) standard 6892, including 0.2% yield strength, ultimate tensile strength, elongation, and fracture analysis. The microstructures of the specimens were evaluated by using metallurgical microscopy, X-ray diffraction (XRD), and scanning electron microscopy. The Tukey honest significant difference test (alpha=.05) was used to statistically analyze the 0.2% yield strength, ultimate tensile strength, and microhardness values. Results. The microstructures of the SLM specimens exhibited homogeneously distributed fine grains, dispersed second-phase particles, and few defects, and the XRD results showed the alpha-Co phase predominated, with minimal epsilon-Co phase and no harmful needle sigma phase in the SLM group. The mean +/- standard deviation of the 0.2% yield strength of the SLM specimens was 790 +/- 11 MPa, and the ultimate tensile strength was 1072 +/- 18 MPa. These values exceeded those of the CAST and CNC specimens by approximately 50% (P<.05). The SLM group showed the highest microhardness (475.3 +/- 10.2 HV10), followed by the CNC (325.2 +/- 17.8 HV10) and CAST group (323.7 +/- 27.2 HV10). Additionally, the ductility and toughness of the SLM specimens were also better than those of the other 2 groups. No significant differences were found in the mechanical performance between the CNC and CAST specimens (P >.05). Conclusions.The microstructures and mechanical properties of Co-Cr dental alloys were dependent on the fabrication techniques. The SLM specimens exhibited better microstructures and mechanical properties than those fabricated with CNC or CAST.