Development of Functionally Gradient Materials via Powder Metallurgy

Powder Metallurgical (P/M) processing of thermal-stress relief type of functionally gradient materials (FGM) was reviewed on the basis of the work achieved by the authors' laboratory of Tohoku University. The role of thermal stress relaxation function in thermal barrier performance was emphasized. The processing routes of FGM were briefly summarized, in which the sintering balance for different mixing conditions of metals and ceramics and the fineness of compositional profile were mentioned. Spray deposition technique and differential temperature sintering have been developed of material species. The characteristic microstructural transition in a graded materials and the accompanying property transion were demonstrated. Two aspects in designing an optimum compositional profiles were described for the reduction of the thermal stress generated during processing ( during cooling from sintering temperature) and in a temperature gradient of thermal barrier situation. Two kinds of thermal loading tests were applied for the evaluation of thermal barrier performance of P/M FGM; a thermal shock test and a differential thermal loading test. The thermal stress conditions during the testing were discussed.