ENVIRONMENTAL STABILITY OF INTERMETALLICS

金属间化合物在实际应用中，除了强度和塑性外，其在环境中的稳定性也受到关注。环境中的氢和氧引起的高温氧化和脆化是最重要的现象。为了提高TiAl合金的高温抗氧化性能，研究了添加微量合金元素和表面处理，或两者结合的方法。添加少量的Hf和Zr（0.2-0.5mass%）可提高合金的抗氧化性，直至1300 K。表面改性由30 μ m厚的涂层的Co-30 Cr-4Al与磁控溅射增加抗氧化性高达1300 K。合金元素（0.2mass%Hf）的加入和表面处理（Cr_2O_3/Cr包埋）的结合可显著提高合金的抗氧化性能。合金元素对金属间化合物氢脆的抑制 关于我们 元素及其作用机理进行了研究。在Ni_3（Si，Ti）中加入少量的B和C，可抑制其在大气中和沸水中的脆化，也可部分抑制其在氢气中的脆化。氢原子在晶界的聚集和氢在晶格中扩散率的降低被认为是抑制晶界断裂的原因。在Ni_3（Si，Ti）中加入少量Cr、Mn、Fe，可抑制其脆性。Fe和Al的加入抑制了Co_3Ti的脆化，其作用机理是抑制了表面水分解为氢原子。本文用Ni_3（Al，Ti）和Ni_3（Si，Ti）单晶和多晶研究了环境氢和体内残余氢的作用。极少量（ppm水平）的残余氢引起脆化，并且即使在10 μ m的高真空条件下，来自环境的氢也影响延展性损失<-6>。少

For practical applications of intermetallics, their stability in the environment has been concerned as well as their strength and ductility. High temperature oxidation and embrittlement induced by hydrogen and oxygen which come from the environment are the most important phenomena. In order to improve the high temperatrure oxidation resistance of TiAl which is expected to be utilized in quite near future, addition of minor alloying elements and surface treatment, or combination of both methods were studied. Addition of small amounts of Hf and Zr (0.2-0.5mass%) was found to increase the oxidation resistance up to 1300K.. Surface modification by a 30 mu m thickness coating of Co-30Cr-4Al with magnetron sputtering increased the oxidation resistance up to 1300k. Combination of alloying element addition (0.2mass%Hf) and surface treatment (Cr_2O_3/Cr pack) was found to improve drastically the oxidation resistance.Suppression of hydrogen embrittlement of intermetallics by addition of alloying … More elements and its mechanism have been studied. Addition of small amount of B and C to Ni_3 (Si, Ti) was found to inhibit the embrittlement in the atmosphere and distillled water and also to suppress partly the embrittlement in hydrogen gas. Aggregation of hydrogen atoms at grain boundaries and decrease in hydrogen diffusivity in lattice were suggested to suppress grain boundary fracture. Addition of small amount of Cr, Mn and Fe to Ni_3 (Si, Ti) was found to inhibit the embrittlement. The embrittlement of Co_3Ti was suppressed by addition of Fe and Al, the role of which was explained rationally by suppression of water dissociation to hydrogen atoms on the surface. The role of hydrogen from the environment and residual hydrogen in the bulk was studied by using Ni_3 (Al, Ti) and Ni_3 (Si, Ti) single or poly crystals. Extremely small amount ( ppm level) of residual hydrogen caused the embrittlement, and hydrogen from the environment affeted on ductility loss even at the high vacuum condition of 10^<-6> torr. Less