| With the development of modern science and technology, on the material properties of the increasingly high demand in the aerospace, nuclear reactors and other fields, high strength, high hardness and excellent high temperature mechanical properties of materials has been growing attention to the metal materials high temperature performance is difficult to meet people's needs, special ceramics into sight. The ceramic material in addition to the characteristics of high hardness, it also has excellent high temperature performance, so gradually in some hot areas of attention has been paid. Silicon nitride is an excellent representative of ceramic materials, because of its good high temperature mechanical properties, excellent chemical stability and good corrosion resistance, has aroused extensive attention.It's well known that ceramic materials although the high temperature, abrasion and chemical resistance and a series of excellent performance, but because of its fatal weakness-brittle, and limit its excellent performance of the play, and therefore limits its application. Therefore, the toughening of ceramic materials in recent years has become the core issues of ceramic materials. So far, of the several ways of toughening ceramics, and has achieved remarkable results. Toughening of ceramics can be divided into two types:one is self-toughened ceramics, it is by sintering or heat treatment process from birth to the internal microstructure of the toughening phase (fraction). The other is the preparation of the sample group to join the second phase element, in order to achieve the purpose of toughening.In this study, alumina and yttria as sintering aids, the use of liquid phase sintering method, and by mechanical property test, electron microscopy and a series of techniques to study the self-toughening, the second phase particle toughening, phase change and mixed toughened toughening silicon nitride ceramic materials and other aspects of the impact, in order to improve the performance of silicon nitride ceramics, from the microscopic structure of its control, to achieve the silicon nitride material conditions of use. This paper is divided into two parts:the preparation of silicon nitride ceramics and performance testing. The main results are as follows:1. Nitride ceramic in the sintering process, sintered powder should be buried to avoid high temperature, silicon nitride decompose and become a single mass.2. In the mechanical properties of self-toughening ceramic study, rod-likeβ-Si3N4 added benefit of elongated grain formation and growth, regulating the material microstructure, silicon nitride ceramics to improve strength and toughness. And, with increasing the content ofβ-Si3N4, Si3N4 ceramics gradually homogenized microstructure, density and mechanical properties are first increased and then decreased, while (3-Si3N4 content of 40%, the density and mechanical properties of ceramic while achieving the way (93% density, transverse rupture strength 583.4MPa, fracture toughness 5.42MPa.m.1/2).3. To MoSi2 particulate material as the second phase toughening silicon nitride materials, the results show:With the increase of MoSi2 content, silicon nitride materials, the density and bending strength decrease simultaneously, indicating that nitrogen is not MoSi2 toughening of silicon materials.4. to SiC particles as reinforcement, the second phase particles of Si3N4 ceramic toughening of the mechanical properties and microstructure. The results show:With the increase of SiC content, Si3N4 ceramics relative density and transverse rupture strength also decreased. When the SiC content is 0, Si3Nt ceramics relative density and transverse rupture strength is maximum. Note, SiC relative Si3N4, it is a difficult phase sintering, SiC addition on sintering of composite materials from the impediment.5. ZrO2 particles as reinforcement to study the ZrO2 content on the properties of silicon nitride ceramics. The results show that:with the increase of zirconia content, increased density of silicon nitride ceramics; transverse rupture strength and fracture toughness first increases and then decreases, when the content reached 10% ZrO2, Si3N4 transverse rupture strength and fracture toughness while the maximum value,respectively,362MPa and 7.0MPa.m1/2.Microstructure of fracture surface observations showed that the improvement of toughness of zirconia from the stress induced transformation toughening.6. Mixed series, bothβ-Si3N4 and ZrO2 as a reinforcement to improve the performance of Si3N4 ceramics. The results show:mixed series of ceramic density and mechanical properties of both the minimum and appear abnormalβ-Si3N4 grain growth, with the expected findings. |
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