Phase maps of Co–Cr alloys bonded to dental porcelain cycled through an incremental number of porcelain firings at two separate thicknesses (0.5 and 1 mm) were analyzed. Bulk hexagonal close-packed (hcp) phase vol% of the alloy was found to increase with the number of porcelain firings for both 0.5 and 1 mm specimens. At the metal-porcelain interface, a uniform fine-grained hcp phase was observed. The depth and grain size of this hcp layer increased with the number of porcelain firings with the thicker specimens undergoing more substantial growth and transformation. Simple heat transfer modeling of the specimens during heat treatment cycles indicated that the thicker specimen had more time at high temperature to affect the face-centered cubic to hcp phase transformation. Therefore, the amount of porcelain firings and the thickness of the alloy should be considered and kept to a minimal when manufacturing metal-porcelain restoration.
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The authors wish to thank the assistance of Brent Pooley from Geology, University of Otago and Jin Yoo from Faculty of Dentistry, University of Otago for their assistance with some specimen preparation.
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Li, K.C., Prior, D.J., Waddell, J.N. et al. Microstructure, phase content, and thermal stability of a cast Co–Cr dental alloy after porcelain sintering cycles using electron backscatter diffraction. Journal of Materials Research 30, 2188–2196 (2015). https://doi.org/10.1557/jmr.2015.178