Pressureless sintering of ZrO2–ZrSiO4/NiCr functionally graded materials with a shrinkage matching process

Shrinkage matching was applied as the basic concept for the processing of five-layered ZrO2–ZrSiO4/NiCr functionally graded materials (FGMs) by pressureless sintering. Shrinkage behavior of the constituent layers of FGM was matched based on the strategy of reducing the mismatches of shrinkage rate between the adjacent layers by a systematic adjustment of the ZrSiO4 inclusion content and the particle size of ZrO2 matrix. Before shrinkage matching, sintering defects such as warping towards the ceramic-rich side of FGM and cracking in the 100 vol% ceramic layer were generated, due to the relatively high mismatches of shrinkage rate between the ceramic- and the metal-rich sides and at the interface of 100 and 75 vol% ceramic layers, respectively. After shrinkage matching, FGMs without any sintering defects were obtained, whereas the green bodies warped towards the metal-rich side already before sintering, due to the relatively higher shrinkage of the metal-rich side during isostatic pressing.