Metallic Materials by means of Localized Hydrogen Distribution and Nanoscopic Damage Analyses

先进的金属材料对环境非常敏感，为了弄清金属材料在使用环境中的降解机理，提高金属材料的韧性，必须弄清材料中氢的进入过程和氢阱的位置。本课题采用氢的热解吸光谱法和原子力显微镜对脆性过程的纳米级原位观察；热解吸光谱分析的是材料中氢的状态，或氢阱位置，材料中负责的氢与氢脆相关。阴极充电提高了TiAl的析氢速率，温度峰低，温度峰高。较低温度下的峰与氢化物分解和微观结构缺陷（如微孔洞）中氢的脱集有关。As接收材料在更高的温度下也呈现出一个演化峰，且演化速率几乎与阴极充电无关。此外，在800℃以上的高温下，阴极充电可以提高析晶速率。这些氢被认为对裂纹扩展加速有重要作用。在干燥空气中，脆化裂纹的裂纹尖端位移（CTOD）小于疲劳裂纹，表明脆化裂纹比由应力强度因子决定的疲劳裂纹具有更尖锐的裂纹。而脆性裂纹的CTOD受材料结构和材料中局部氢含量的影响，具有较大的散射带。静态SC裂纹沿晶界扩展时，裂纹沿晶界沿瓮状顺序稳定扩展，无迟滞现象。随着CTOD的增大，裂纹扩展速率逐渐减小。当裂纹扩展超过三晶界时，CTOD随裂纹扩展速率的增大而减小。施加阴极电流时，试样表面附近的裂纹路径为穿晶，裂纹扩展呈锯齿形，且由于材料中局部含氢量的影响，裂纹扩展呈瓮级加速和滞后。少

Advanced metallic materials are sensitive to an environment and in order to clarify the degradation mechanisms and to improve the toughness of these metallic materials in a service environment, we must clarify the process of hydrogen entry as well as the hydrogen trap sites in the material. In this research project, thermal desorption spectroscopy of hydrogen and nanoscopic in situ observation of the process of embrittlement by means of atomic force microscopy are applied; the thermal desorption spectroscopy analyze the state of hydrogen in the material, or hydrogen trap sites, and the responsible hydrogen in the material is correlated to hydrogen embrittlement. The hydrogen evolution rate of TiAl is increased by cathodic charging, with lower temperature peaks and higher ones. The peaks at lower temperatures are correlated with hydrides decomposition and detrapping of hydrogen from microstructural imperfections such as microvoids. As received materials also shows an evolution peak at a … More higher temperature, and the evolution rate is almost independent of cathodic charging. In addition, the evolution rate at a higher temperature above 800 ℃ is increased by cathodic charging. These hydrogens are considered to have an important role on crack growth acceleration. The crack tip displacement (CTOD) of the embrittled crack is smaller than that of a fatigue crack in dry air, indicating that the embrittled crack has sharper crack than that of fatigue crack that is determined by the stress intensity factor. However the CTOD of the embrittled crack has large scatter band because the CTOD is influenced by the structure of the material and the localized hydrogen content in the material. The static SC crack grows in a steady manner in the order of urn without any retardation, when it grows along the grain boundary. However, the crack is reaching the triple grain boundary, the crack growth rate is decreasing with an increase in the CTOD. However, the crack passes over the triple grain boundary, the CTOD is decreased with an increase in the crack growth rate. When the cathodic current is applied, the crack path near the sample surface is transgranular, and the crack grows with a zigzag manner, and the crack grows with acceleration and retardation in the order of urn due to the amount of the localized hydrogen content in the material. Less