1985 Volume 3 Issue 1 Pages 104-109
As a basic research of diffusion bonding between dissimilar materials which have the marked difference in coefficients of thermal expansion, diffusion bonding of WC-Co hardmetal to steel has been carried out.
Thermal stresses generated as a result of the difference in the coefficients of thermal expansion of the hardmetal and the steel during the cooling of bonded parts have been estimated by. the theory of thermal elastic analysis based on the finite element method. Tensile strengths of the bonded joints have been also discussed on the effects of thermal stress, interlayer thickness and cooling rate after bonding.
It is found from the result of the calculation that a maximum tensile stress is generated on the surface of the bonded hardmetal. Therefore, the bonding strength seems to be lowered by the thermal stress.
The use of an interlayer affected the bonding strength. The bonding strength increased through a maximum at 0.25 mm thickness of the interlayer then decreased with increasing the thickness. The improvement of the bonding strength is due to the decrease of the thermal stress.
The bonding strengths were improved at faster cooling rates than 13°C/min. The improvement of the bonding strength was interpreted by the decrease of the thermal stress whihc is due to the expansion of the bonded steel caused as the result of the martensite transformation during cooling.