Theoretical model of the transformation superplastic diffusion bonding of eutectoid steel

Based on current theories of diffusion and creep cavity closure at high temperature, a theoretical analysis of phase transformation diffusion bonding for T8/T8 eutectoid steel is carried out. A new theoretical model is established for the process of transformation superplastic diffusion bonding (TSDB) on the basis of a theoretical model for isothermal superplastic diffusion. The model can predict the bonding quality, which is affected by technological parameters, such as the limit cycling temperature, the compressive stress, the number of thermal cycles and temperature cycling through the phase transformation in the thermal cycle, and so on. The result show that the maximum temperature, the compressive stress, the numbers of thermal cycles and the rate of temperature change in the thermal cycle have an important influence on the TSDB process. At the same time, reasonable technological parameters chosen from the theoretical analysis are seen to be in good agreement with those obtained from experimental results.