Temperature profile optimization for microwave sintering of bulk Ni–Al2O3 functionally graded materials

Bulk multilayer graded Ni–Al2O3 samples have been sintered under heating by millimeter-wave radiation using a gyrotron system for high-temperature materials processing. By using a purposely designed thermal insulation arrangement, the temperature profile has been adjusted along the concentration gradient to accommodate for different sintering temperatures of the components. The sintered samples have flat boundaries between layers, and their microstructure is free from cracks and delamination. In addition to metal-ceramic graded transitions, metal-ceramic-metal graded insulator structures have also been fabricated.