Mo-Si-B三元系中T2相的力学特性及其机制

项目名称： Mo-Si-B三元系中T2相的力学特性及其机制

项目编号： No.50871012

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 生物科学

项目作者： 张来启

作者单位： 北京科技大学

项目金额： 39万元

中文摘要： T2相是Mo-Si-B两个热点三相合金重要的组成相，但是由于纯T2相制备困难，对其研究较少，尤其力学特性更为甚少。项目在对原位合成T2相热力学计算、元素粉末除氧热力学和工艺研究的基础上；首次系统研究了Mo-Si-B三元系反应合成的相形成贯序和组织演化规律，实现并优化了一种利用三元素粉末固-液反应、相组成可控的SPS原位反应热压工艺（已申请专利），获得了晶粒细小、高致密的纯T2相合金；利用第一原理计算了室温力学特性；考察了不同温度压缩流变行为；测量了室温维氏硬度；确定了压痕法测量T2相断裂韧性专用方程；用压痕法、三点弯曲法表征了不同温度断裂韧性，探讨了断裂行为。获得了T2相的力学特性基础数据及其机制。1400℃#30340;屈服强度、断裂韧性分别为309MPa、8.28 MPaom1/2。T2相本征脆性的原因是在Mo、Si原子围成的三角区域和Mo、B原子围成的八面体内分别存在定域共价键，这两个共价键交替排列，使得原子难以移动，位错滑动困难，最终导致脆性。高温压缩变形机制是扩散性蠕变。室温、中温、高温断裂机制分别是穿晶解理断裂、穿晶解理-沿晶混合断裂、沿晶断裂。为更加全面认识和利用T2相提供重要依据。

中文关键词： Mo-Si-B三元系；T2相(Mo5SiB2)；原位反应热压；力学特性；机制

英文摘要： The T2 phase is a key phase component of the two research-focus tri-phase alloys. However it especially its mechanical characteristics has been paid less research attention to because it is very difficult to fabricate the pure T2 alloy. Based on the thermodynamic calculations of synthesizing T2 phase in-situ and the investigation of thermodynamics and process of removing oxygen from raw elemental powders, the phase forming order and microstructure evolution of reaction synthesis in Mo-Si-B ternary system was systematically studied for the first time. The SPS In-situ Reactively Hot-Pressing technology by which the phase component can be controllable was realized and optimized using solid to liquid reaction of elemental powders. The pure T2 alloy with small grains and high density was obtained. The mechanical characteristics at room temperature was calculated by the fist-principle. The compressive deformations at different temperatures and Vickers Hardness at room temperature were measured. The special equation of the measurement of T2 phase fracture toughness by indentation method was determined. The fracture toughness values at different temperatures were characterized by indentation method and three-point bend method respectively. The fracture behavior was discussed. The basic data of mechanical characteristics and mechanism of T2 phase were acquired. The yield strength and fracture toughness at 1400℃is respectively 309 MPa and 8.28 MPaom1/2. The reason of the intrinsic embrittlement of the T2 phase is that two kinds of covalent bonding respectively in the triangle area enclosed by Mo and Si atoms and in the octahedron encircled by Mo and B atoms, arranging alternately, lead to being unmovable of atoms and non-sliding of dislocations, and the ultimate embrittlement of T2 phase. The deformation mechanism at high temperature is diffusive creep. The fracture mechanisms at room, medium temperature and high temperature are transgranular cleavage, mixture of transgranular cleavage and intergranular fracture, and intergranular fracture respectively. These results will provide an important guidance for the comprehensively understanding and reasonably utilizing of T2 phase.

英文关键词： Mo-Si-B ternary system;T2 phase(Mo5SiB2);In-situ Reactively Hot-Pressing; mechanical characteristics;mechanism