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

先进的金属材料对环境很敏感，为了弄清这些金属材料的退化机理并提高其在使用环境中的韧性，我们必须弄清楚氢进入材料的过程以及材料中的氢陷阱位置。在本研究项目中，氢的热脱附谱和原子力显微镜下的纳米原位观察脆化过程；热脱附谱分析了材料中氢的状态或氢陷阱位置，并将材料中负责的氢与氢脆相关联。阴极充电提高了TiAl的析氢速率，具有较低的温度峰和较高的温度峰。较低温度下的峰与氢化物的分解和氢从微结构缺陷(如微孔洞)中的脱陷相关联。AS接收到的材料也在…处显示出演化峰值温度越高，析出速率几乎与阴极充电无关。此外，在800℃以上的较高温度下，阴极充电提高了析出速率。这些氢被认为对加速裂纹扩展具有重要作用。在干燥空气中，脆性裂纹的裂纹尖端位移(CTOD)小于疲劳裂纹的CTOD，表明脆性裂纹的裂纹尖端比疲劳裂纹的尖端尖端尖锐，这是由应力强度因子决定的。然而，脆性裂纹的CTOD受材料结构和材料中局域氢含量的影响，具有较大的散射带。静态SC裂纹沿晶界扩展时，沿晶界稳定地以金银柱的顺序扩展，没有任何滞后现象。然而，裂纹已达到三重晶界，裂纹扩展速率随着CTOD的增加而减小。然而，当裂纹越过三重晶界时，CTOD随裂纹扩展速率的增加而减小。当施加阴极电流时，样品表面附近的裂纹路径是穿晶的，裂纹以之字形方式扩展，并且由于材料中局部含氢量的增加，裂纹以金银柱的顺序加速和滞后扩展。较少

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