Measuring residual stress and its influence on properties of porous ZrO₂/(ZrO₂+Ni) ceramics

Ceramic-metal functionally graded materials (FGMs) have been extensively used in aerospace engineering where high strength and excellent heat insulation materials are desired. However, their performance highly depends on the internal residual stress, which is generated inevitably due to the thermal mismatch of ceramic and metal. In this paper, based on the nanoindentation test, the field distribution of the residual stress of porous ZrO₂/(ZrO₂+Ni) ceramic-metal FGMs is measured. The residual stress field measured by nanoindentation agrees qualitatively with the finite element simulation results. Then a constitutive relation is established to investigate the effects of residual stress on the macroscopic deformation behavior of porous ZrO₂/(ZrO₂+Ni) FGMs, which agrees well with the bending and compression experiments. It is found that residual stress can improve both the flexural strength and stiffness of the porous ZrO₂/(ZrO₂+Ni) FGMs, by densifying and compensating the tensile stress of the porous middle layer (ZrO₂) during the bending process, respectively. However, it has no obvious influence on the ultimate compressive strength of the porous ZrO₂/(ZrO₂+Ni) FGMs, but mainly influences its initial stage of elastic deformation in the compressive behavior.