Papers by Author: Zhen Sheng Qu

Abstract: Based on preparing large bulk Al2O3/ZrO2 (4Y) eutectics, SiO2 additive is used for controlling the microstructures, densification and mechanical properties. XRD pattern showed SiO2 additive in the ceramics was in the form of glass phase. SEM images showed that the microstructure morphologies transformed from the cellular eutectics to the rod-shaped colonies with increasing content of SiO2 additive. With increasing content of SiO2 additive, the relative density of the ceramics increased whereas the hardness of the ceramics decreased. As the content of SiO2 additive reached 4%, fracture toughness of the ceramics had the maximum value due to the coupled toughening mechanisms of crack-pinning, crack- bridging and crack-deflection by rod-shaped colonies. As content of SiO2 additive reached 6%, the highest flexural strength of the ceramics was achieved due to high fracture toughness and small-size critical defect.

Abstract: Based on preparation of Al2O3/ZrO2 (4Y) by combustion synthesis in high-gravity field, the microstructure transformation and properties of the materials are investigated through adjusting the ZrO2 (4Y) content in the composites. As the content of ZrO2 changed from 37% to 40%, the microstructures of the ceramics transformed the sphere-like tetragonal ZrO2 crystals from the rod-shaped colonies with nanocrystalline structures. Al2O3/33%ZrO2 (4Y) had the maximum relative density, hardness and flexural strength due to the low solidification temperature, the highest volume fraction of the colonies, small-size defect and high fracture toughness, whereas Al2O3/44%ZrO2 (4Y) was somewhat weakened in strength in despite of its highest fracture toughness.

Abstract: The large-bulk solidified TiC-TiB2 composites were prepared by combustion synthesis in high-gravity field. XRD, FESEM, SEM and EDS results showed that TiC-TiB2 composites were mainly composed of TiC matrix in which a number of fine TiB2 platelets were embedded, surrounded by the boundary regions consisting of (Cr, Ti) C0.63 carbides. The hardness, flexural strength and fracture toughness of TiC-TiB2 composites measured 28.5GPa, 750±25MPa and 6.2±0.5MPa•m1/2. High hardness of the composites benefits from the absence of the intermediate borides and the achievement of stoichiometric TiC phases due to rapid solidification, whereas the achievement of high strength benefits the refinement and homogeneity of the microstructures due to rapid separation of liquid oxides in high-gravity field and rapid coupled growth of TiC and TiB2 phases.

Abstract: The large bulk Al2O3/ZrO2 (Y2O3) eutectics were achieved by combustion synthesis in high-gravity field. With increasing high-gravity level, the matrix of eutectics transformed the rod-shaped colonies from the cellular ones, and the nanocrystalline microstructures came into existence as the high-gravity level was larger than 200g. The relative density, hardness, flexural strength and fracture toughness increased simultaneously with increasing high-gravity level, and reached the maximum values of 98.6%, 18.6GPa, 1248MPa and 15.6MPa•m1/2 respectively as the high-gravity level was 250g.