Abstract:

Objective To study the effect of solid phase transformation on the metal-ceramic compatibility of Co- Cr alloy during firing programs. Methods 9 foils of Co-Cr and Ni-Cr alloy with the dimension of 25 mm×3 mm×0.5 mm were casted using lost wax technology respectively. Among them, 6 specimens were subjected to metal-ceramic bonding strength test（three point bending method）, the ceramic layer of 3 specimens were removed for X-ray diffraction（XRD） analysis. One cylindrical specimen of each alloy was casted for the test of coefficient of thermal expansion, cooling curves were recorded. Results The metal-ceramic bonding strength of Ni-Cr, Co-Cr alloy was （49.1±3.40）, （40.9± 2.02）MPa respectively. There was significant difference between the two groups’bonding strength（P=0.00）. The coefficient of thermal expansion in the 20-500 ℃ interval of Ni-Cr and Co-Cr alloy was 13.9×10-6, 13.8×10-6·K-1 respectively. XRD analysis indicated that the microstructure of Ni-Cr alloy was austenite. While Co-Cr alloy was constituted by fcc phase, hcp phase and σ phase. Conclusion During the cooling procedure, the transformation of fcc phase to hcp phase and segregation of needle-like σ phase intensify the linear contraction speed of Co-Cr alloy, which decreases
the metal-ceramic adaptability.

Key words: metal-ceramic bonding, Co-Cr alloy, coefficient of thermal expansion, solid phase transformation