DISLOCATION MECHANISMS FOR THE RELAXATION OF THERMAL-STRESS AT METAL CERAMIC INTERFACES

Thermal stresses in the vicinity of the interface between metal and ceramic components result from the difference in the thermal expansion coefficients between the two materials when the temperature is changed. The dislocation structure in and near NiO-Pt interfaces that survived large temperature changes was studied in order to understand how a metal-ceramic couple accommodates thermal stresses that frequently can exceed the yield stress of the metal and the fracture stress of the ceramic. The interface structure for the exact (001) epitaxial orientation relationship between Pt and NiO is a square grid of misfit dislocations. A larger misfit dislocation spacing is expected to be present at room temperature than at the high temperature used during hot pressing to form the metal-ceramic bond. A dislocation mechanism based on climb and glide was suggested to produce this change of spacing and relieve the thermal stress. Experimental observations were obtained which are consistent with this mechanism.