Effects of constituent

thermal expansion coefficient and solid phase transformation on the bonding property of porcelain fused to Co-Cr dental alloy were analyzed by XRD（X-ray diffraction）

SEM（scanning electron microscope）and EDS（energy dispersive spectrum）

thermal expansion coefficient and bonding strength testing.The results show that the bonding strength of porcelain fused to Co-Cr alloy reaches 40.9 MPa

exceeding the 25 MPa required by the standard of YY 0621-2008.The microstructure of the alloy is composed of fcc Co solid solution and hcp Co solution and insular intermetallic compound as well as σ phase.Thermal expansion coefficient difference of alloy to ceramic is（0.5

0

.6）×10-6/℃.During firing process

transformation of fcc phase to hcp phase and segregation of acicular σ phase could decrease the compatibility of alloy with ceramic

resulting in the increase of porcelain crack rate and cleft rate.