LAUSR

Abstract The present study aimed to evaluate the microstructural and bending behavior of five-layers FGM structures fabricated by spark plasma sintering under different sintering temperatures. For this purpose, FGM samples containing four layers of Al2O3–Al ceramic matrix alongside an alumina layer were sintered under 40 MPa pressure and three different sintering temperatures 1050, 1400 and 1450 °C. The optimum microstructure with less micro-voids and aluminum islands was observed in the sample with maximum relative density of 90.7%, which sintered at 1450 °C. For the sample sintered at 1050 °C, the amount of porosity reached about 36%, which caused the lowest bending strength of 55 MPa and the maximum bending strain of (6.35%). Indeed, the flexural strength which depends on relative density, controlled by sintering temperature. For instance, the maximum bending strength of ~358 MPa associated with minor elongation (~3.7%) was obtained in sample sintered at the highest temperature. Also, the bending strength results were accorded with the fracture analysis. While the fracture surface of sample sintered at lowest temperature comprised of cracked particles and remarkable voids, the fracture surface analysis of specimens sintered at 1400 °C and 1450 °C illustrated transgranular and intergranular fracture. For the latter samples, the contribution of each fracture mechanism was governed by sintering temperature and chemical composition of layers. Considerably, sintering at 1400 °C prevents grain growth and extends weak boundary, which tends to intergranular fracture. In addition to temperature, the presence of aluminum reduced the strengthen ceramic/ceramic bonds, and consequently, motivated intergranular fracture in layers having further metal constituent.