Study On The Fabrication And Properties Of ZrB₂-SiC Laminated Ultra-high Temperature Ceramics

Ultra-high temperature ceramics?UHTCs? are mainly used in aerospace field and weapons system. It is a research hotpots at present about how to improve the high temperature performance and prepare new composite materials. Laminated structure has attracted a great deal of interest in ceramic field, since laminated ceramics appeared. Laminated ceramics have many advantages, such as anisotropy, easy to cleavage between the layers, simple preparation process and adjustable composition spatial distribution. In this study, the laminated structures are introduced into the fabrication of Zr B₂-SiC laminated ultra-high temperature ceramics. And the microstructure, mechanical properties, anti-oxidant, anti-ablation and oxidation mechanism are investigated. At the same time, the differences of performances are compared between ZrB₂-SiC laminated ultra-high temperature ceramics and ZrB₂-Si C monolithic ultra-high temperature ceramics and the reasons of the differences are analyzed.ZrB₂-Si C laminated ultra-high temperature ceramics are fabricated by tape casting and vacuum hot-pressing sintering method with ZrB₂ powder and SiC powder. The medium includes PVB and PEG. The first step for successful preparation of ZrB₂-SiC laminated ultra-high temperature ceramics is to determine the preparation process. According to the DSC curve, 600°C is the best temperature to remove the binder. Zr B₂-SiC laminated ultra-high temperature ceramics can be successfully prepared by vacuum hot-pressing sintering under 1700°C/30 MPa and 1800°C/30 MPa with the holding time of 90 min. And all aspects of the performances are improved when the sintering temperature became 1800°C/30 MPa, such as microstructure and flexural strength which has been improved to 283 MPa. Therefore, the followed studies use the sample fabricated under 1800°C/30 MPa.In order to investigate the effect of laminated structure for ultra-high temperature ceramics, ZrB₂-SiC laminated ultra-high temperature ceramics and the ZrB₂-Si C monolithic ultra-high temperature ceramics with the same preparation process of laminated material are compared. The results are listed in follow: laminated materials show the typical non-catastrophic fracture and the crack deflections can be clearly observed when the material fracture. The fracture way of monolithic materials is typical brittle fracture. The bending strength is slightly lower of laminated materials than monolithic materials. Laminated materials show a absolute advantage in anti-oxidant and anti-ablation due to its particular structure. Layer structure can effectively prevent oxygen diffusion and the formation of oxide film will cut off the spread of oxygen to the inside material. The content of oxygen in the laminated materials from outside to interior is decreased significantly and there is no regular trend for monolithic materials. Oxidation mechanism of monolithic materials is unordered defect oxidation. The laminated materials are oxidized layer by layer. As a result, the laminated structure can greatly prolong the service life of materials in a high temperature oxidation environment.