Environmental Strength Evaluation and Investigation into Degradation Mechanisms of Advanced Metallic Materials based upon Analyses of State of Hydrogen and Nanofractography

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，氢的热脱附谱被用来分析材料中氢的状态，或氢陷阱位置，并将材料中负责的氢与氢脆相关联：所研究的材料为钛铝化物金属间化合物和Ti-6Al-4V合金，并研究了环境对疲劳裂纹扩展行为的影响。在钛铝化物的情况下，双相材料的拉伸强度在环境中按水分子含量的顺序下降：真空中的强度最高，按实验室空气和水的顺序下降。在层状材料的情况下，疲劳c…在干燥空气中，R-C裂纹面方向的齿条扩展速率高于L-C裂纹面方向：裂纹扩展速率随裂纹的剥离而增大。然而，对于双相材料，在低ΔK(ΔK_&lt；Off&gt；)区，R-C裂纹面方向的裂纹扩展速率较小。当施加阴极充电时，疲劳裂纹扩展速率比在干燥空气中更高，特别是在较高的应力强度因子范围内。阴极充电提高了析氢速率，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接收材料在较高温度下也有一个演化峰，演化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。这些氢被认为在加速疲劳裂纹扩展方面起着重要作用。相反，当裂纹平面取向为T-L时，Ti-6Al-4V合金的裂纹扩展速率对环境敏感，而在溶液中的裂纹扩展速率与在干燥空气中的裂纹扩展速率几乎相等。然而，当施加的应力强度因子范围超过一定值时，裂纹路径向纵向改变。氢析出动力学与试验环境无关，也与裂纹扩展的加速无关，并对裂纹加速的机理进行了讨论。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 hydrogens is applied to analyze the state of hydrogen in the material, or hydrogen trap sites, and correlate the responsible hydrogen in the material to hydrogen embrittlement : the materials investigated are titanium aluminides intermetallic compound and Ti-6Al-4V alloys, and the influence of environment on fatigue crack growth behavior was investigated. In the case of titanium aluminides, the tensile strength of the duplex material decreases in order of a water molecule content in an environment : the strength in vacuum is the highest, and decreases in order of laboratory air and water. In the case of the lamellar material, the fatigue c … More rack growth rate in dry air is higher in the R-C crack plane orientation than that in L-C crack plane orientation : the crack growth rate becomes higher when the crack grows as the lamellae are tearing off. However, in the case of the duplex material, the crack growth rate in the R-C crack plane orientation is smaller in low ΔK (ΔK_<off>) region. When the cathodic charging is applied, the fatigue crack growth rate becomes higher than that in dry air, in particular at higher stress intensity factor range. The hydrogen evolution rate 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 a evolution peak at a 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 fatigue crack growth acceleration. In contrast with these, the crack growth rate of Ti-6Al-4V alloy is sensitive to environment when the crack plane orientation is T-L, whereas the crack growth rate in a solution is almost equal to that conducted in dry air. However, the crack path changes towards the longitudinal direction, when the applied stress intensity factor range exceeds a certain value. The hydrogen evolution kinetics are independent of the testing environment, or the acceleration of crack growth, and the mechanisms of the crack acceleration are discussed. Less