Bond strength and interfacial analysis of six CoCr alloys made by conventional casting and selective laser melting

Abstract

Purpose: To investigate the effects of the elemental composition and the manufacturing process of cobalt chromium–molybdenum (CoCr–Mo), cobalt chromium–tungsten (CoCr–W), and CoCr–Mo-W alloys on metal–ceramic bond strength. Materials and Methods: Six CoCr-based alloys were included in this study, a were classified into three different groups depending on their elemental composition (Ν = 10, for each group). The first group had molybdenum (Mo) as the third alloying element, the second group contained tungsten (W) (without Mo), and the third group included both alloying elements. The groups were further divided by the manufacturing process (casting or selective laser melting, SLM). Interfacial analysis was carried out using backscattered electron imaging (BEI) and energy-dispersive X-ray microanalysis (EDX) operating in line scan mode. The metal-ceramic bond strength was tested by a 3-point bending test according to the ISO 9693 requirements. The fracture mode of all specimens was examined under a stereomicroscope. The bond strength results were statistically analyzed by 2-way ANOVA and Tukey's multiple comparison post hoc test (a = 0.05). Results: A continuous interface with the porcelain was found without pores, debonding areas, or other defects. Of the major elements found at the interface, Co showed the highest diffusion rate, while titanium (Ti) had the lowest diffusion rate. No statistically significant differences were identified in metal-ceramic bond strength either among materials or between manufacturing processes. The fracture mode was found to be cohesive for all specimens. Conclusions: The metal-ceramic bond strength is independent of the current CoCr alloy type and manufacturing process when comparing conventional casting and SLM. Interfacial analysis revealed no differences between the tested groups.