Abstract: For solid state bonding, the faces of ceramic and metal parts to be bonded re placed together, acted upon by a gage pressure if desired, and are heated to a bonding temperature which is under their melting temperatures so that an inbetween or intermediate layer is formed between the two parts. For increasing the bond strength the metal used is one undergoing a phase transition on cooling down from the bonding temperature, the phase in existence at the bonding temperature having a smaller volume than the phase stable at room temperature, so that the decrease in the volume of the metal as dependent on the coefficient of thermal expansion is balanced at least to some degree by the volume change on phase transition.