Diffusion bonding of zirconia to silicon nitride

The application of diffusion bonding ZrO2 to Si3N4 using a Ni interlayer in an industrial construction was studied. The optimal process parameters were determined in laboratory experiments. The optimal conditions were selected by evaluating the shear strength of bonds made under different process conditions. The determined bonding temperature is 1050 degrees C. The bonding pressure and the interlayer thickness do not influence the bonding strength. However, direct application of these conditions in bonding large workpieces results in problems because of residual stresses that appear after cooling the bond. These stresses originate in the difference in thermal expansion of the two ceramics and cause cracks in the ZrO2. It was found that the stress level in the construction can be reduced by applying a thicker interlayer. Furthermore, indications were obtained that the introduction of a recrystallisation period during cooling at 750 degrees C causes relaxation of the residual stresses in the nickel.