Fabrication of a PSZ-Ti functionally graded material by spark plasma sintering and its fracture toughness

This paper deals with fracture behavior of a partially stabilized zirconia (PSZ) - pure titanium (Ti) functionally graded material (FGM) fabricated by spark plasma sintering (SPS) technique. The PSZ-Ti FGM in which PSZ content is reduced from PSZ surface to Ti substrate in a stepwise manner was fabricated, and its fracture toughness distribution was evaluated. Large voids and delamination were not observed in the graded layer of the fabricated FGM. The Ti substrate and PSZ surface maintained original hardness of the monolithic Ti and PSZ fabricated by SPS respectively, and the hardness in the graded layer decreased with increasing Ti volume fraction. In fracture toughness tests, unstable crack growth occurred from a small starter-crack in the PSZ surface through the graded layer and stable crack growth occurred in the Ti substrate. The fracture toughness in the Ti substrate increased with being apart from the interface between the graded layer and Ti substrate. These results revealed that the PSZ-Ti FGM had an ability to arrest crack propagation in the Ti substrate.