The Effect of Crystal Structure and Microstructure on the Hydrogen-Induced Embrittlement of Intermetallic Compounds

本文采用l1_2型结构的Ni_3（Si, Ti）和Co_3Ti金属间化合物，观察了晶界原子组成、晶粒尺寸和第二相分散度的影响。得到了以下结果：1)利用俄歇光谱分析了Ni_3（Si, Ti）合金晶界处的原子组成，并与合金在空气中的拉伸延展性进行了对比。结果表明，硼等晶界成分及其组成原子对Ni_3（Si, Ti）合金在空气中变形后的拉伸延展性有很大影响。说明晶界富集的硼原子影响了空气中水分的分解过程，或阻碍了氢的迁移和凝聚，降低了环境脆化。2)发现含Nb的第二相分散体虽能提高Ni_3（Si, Ti）合金的强度，但能抑制Ni_3（Si, Ti）合金的湿致脆。对这一结果的解释是，吸收的氢可以被捕获在第二相弥散体中，或者在第二相弥散体与基体之间的界面上，或者在第二相弥散体相邻的塑性变形区域。在此基础上，开发了具有高低温断裂韧性和高高温流动强度的高温结构材料。3)细晶组织能有效降低Co_3Ti合金的湿脆。在低变形速率区，Co_3Ti合金的湿致脆化程度降低。Co_3Ti合金自由表面形成的氧化及相应的氧化产物减少了空气中水分的分解，导致湿致脆。

Using Ni_3(Si, Ti), and Co_3Ti intermetallic compounds with L1_2-type structure, the influence of atomic composition at grain boundaries, grain size and the second-phase dispersions has been observed in this study. The following results were obtained.1) The atomic compositions at the grain boundaries of Ni_3(Si, Ti) alloy were analyzed by means of Auger spectroscopy, and then correlated with the tensile ductility in air. Consequently, it was found that grain boundary compositions such as boron as well as constituent atoms strongly affected the tensile ductility of Ni_3(Si, Ti) alloy deformed in air. It was suggested that boron atoms enriched at the grain boundaries affect decomposition process of moisture in air, or block the migration and the condensation of hydrogen, reducing the environmental embrittlement.2) It was found that the Nb containing second-phase dispersions suppress the moisture-induced embrittlement of Ni_3(Si, Ti) alloys though those enhance the strength of Ni_3(Si, Ti) alloys. This result was interpreted so that the absorbed hydrogen can be trapped within the second-phase dispersions or at interface between the second-phase dispersions and the matrix, or in the plastically deformed regions adjoining the second-phase dispersions. Based on these results, high-temperature structural material with high fracture toughness at low temperature and also high flow strength at high temperature was developed.3) It was found that fine-grained microstructure was effective in reducing the moisture-induced embrittlement of Co_3Ti alloy. Also, the moisture-induced embrittlement of Co_3Ti alloy was reduced in the low deformation rate region. As a corresponding mechanism, oxidation and related oxide product formed at free surface of Co_3Ti alloy reduce the decomposition of moisture in air, resulting in the moisture-induced embrittlement.