The Study Of Preparation And The Thermal Shock Resistance Of ZrO₂/Ni Gradient Composite Material

In this study, ZrO₂/Ni gradient composite was prepared by vacuum hot-presssintering with ZrO₂powders and Ni powders as raw materials. Themicrostructure and the mechanical properties of this composite were studiedsystematically, by using three-point bending method, SEM and XRD. The mainconclusions are as follows:The optimum preparation process of ZrO₂/Ni gradient composite as follows:1200℃for1h,25MPa in vacuum atmosphere. The combine between the internallayers of the composite is tight. The sample get preferable mechanical properties,and the density, fracture toughness and bending strength reach the maximum, are98.36%、11.7MPa·m1/2and970.40MPa, respectively.There is a gradient change of micro-hardness values of ZrO₂/Ni gradientcomposite from layers of pure Ni to pure ZrO₂. There is no mutation of micro-hardness in ZrO₂/Ni gradient composite because of the gradient change ofcomposition. XRD test results show that there is no compound formed in ZrO₂/Nigradient composite during the sintering. SEM spectrum analysis shows that thereformed a diffusion layer at the interface between two layers during the sintering.Thermal shock resistance test results show that the bending strength of thesample with the sintering temperature of1200℃after thermal shock resistancetest is the best, the value is270.27MPa, about28%of the value before thermalshock resistance test. The mechanical properties and the thermal shock resistanceof the sample are excellent when the sintering temperature is1200℃. Due to thegradient change of the internal composition, the internal stresses of the samplesare moderated and the interfaces between the layers are close. There was no material spalling occurred during the thermal cycles.SEM fracture surface analysis shows that the combination between layers isclose and the fracture mode of ZrO₂/Ni gradient composite is a mixture of brittlefracture of ZrO₂and ductile fracture of Ni. There is no change of fracture modeoccurred during the thermal shock test. However, as the presence of thermalstress in the samples that the cracks are extended easily when external force rolein the samples. The fracture surfaces of layers are more and more flat with theincreasing of ZiO₂content, and the dimple content of Ni layer decreases.