| Supported financially by the National Natural Science Foundation of China, employing the testing techniques such as optical metallography analysis, scanning electron microscope (SEM), electron microprobe scanning microscope (EMSM) , transmission electron microscope (TEM), X-ray diffraction (XRD) and mechanical performance measurements (including micro-yield strength mys) etc., this research has worked comprehensively and deeply on a very important issue ?the micro-yielding behavior and mechanism of beryllium material for inertial guidance instruments and optical mirrors ?which has been paid more attention to by designers since the 8th even the 7th five-year plan. The research has conducted the first relatively systematic study on the manufacturing process, performance and microstructure of beryllium material made in China, through which we have learned basically the mys condition of Chinese beryllium material and the key influencing factors of the mys. The results acquired will play a positive role in designing the mys index of Chinese beryllium material and in promoting and extending the application of beryllium material in aviation, aerospace and navigation. The research findings with regard to the microstructure of beryllium material, especially the micro-yield mechanism based on the analysis of dislocation movement will perfect and enrich the content of the worldwide research on mys mechanism.Utilizing the beryllium powders with steadily low oxygen made by the newest method of impact grinding, the research pioneered the first attempt in the world in studying the effects of the grain size independently on the mys of the vacuum-hot-pressed (HP) beryllium material and the cold-hot-isostatic (HOP) beryllium material. It has been found that whether the beryllium material is produced by HP or HIP, the mys value will rise remarkably as the grain size is reduced, which conforms to the Hall-Petch formula. Compared with the HTPed beryllium material with the same particle size, the hot-pressed beryllium material has lower mys,. value because its higher consolidation temperature will cause grains to grow. The test has also shown that the purer hot-pressed as well as HIPed beryllium materials with less content of Fe and Al impurities mainly consist of two phases-the matrix beryllium and the second phase of beryllium oxide (BeO). The HIPed beryllium material has higher mys value because of not only its lower consolidation temperature and higher consolidation pressure but also the more uniformly and finely dispersed distribution of its BeO phase. The average mys value of the HIP-LS-5 beryllium material, whose grain size is similar to the HEP-50 beryllium material of America, reaches 99MPa, 19% higher than that of the HIP-5O (83MPa), and also superior to 1-250 (97MPa), the new-generation beryllium material for instrument.Beryllium powders with the same particle size and various contents of BeO were prepared by pre-sintering-acid washing processes initiatively and the influence of BeO alone on o mys of beryllium was observed and some new results have been obtained-compared with the content of BeO, the distribution of BeO in beryllium has more critical influence on mys;finely dispersed BeO along the grain boundaries and in the matrix results in the dispersion strengthening of beryllium matrix and thereby the higher mys value; on the contrary, the coarser BeO particles clustering on the grain boundaries results in negative influence on o mys. The test result of the beryllium materials with medium BeO content and high strength and high elongation showed that the mys value of a kind of hot-pressed beryllium material of 2.5% BeO and produced at 1070癈 reaches 71MPa, and its elongation is up to 3.52%, 17% higher than American 1-250 HIPed beryllium material with the same BeO content. It is a useful trial exploration for preparing beryllium material by HIP with integrated properties reaching or exceeding 1-250 in China in the future.The research prepared the beryllium powders with relatively stable Fe co... |
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