HREM Study of high temperature metals and ceramics

金属间化合物和陶瓷材料是一种新型的耐热材料，本文采用高分辨电子显微镜（HREM）、分析电子显微镜（AEM）和电子过滤显微镜（EFEM）对它们进行了研究。本研究所得结果归纳如下。(1)Ni_2AlTi和Ni_2AlHf沉淀相颗粒在NiAl金属间化合物中弥散分布，其蠕变强度比无沉淀相颗粒的NiAl有明显提高（约10个数量级）。高分辨电子显微术揭示了位错与粒子之间的相互作用是一种吸引作用。发现变形的阈值应力约为270 MPa。(2)在NiAl金属间化合物中加入Fe，在较高应力下可有效地提高蠕变强度。高分辨电子显微镜（HREM）结果表明，含Fe的NiAl合金在蠕变过程中形成亚晶界，而不含Fe的NiAl合金在蠕变过程中未形成亚晶界。结果表明，含Fe的NiAl合金的蠕变为合金型，而不含Fe的NiAl合金的蠕变为金属型。(3)结果表明，Mn的加入降低了Ti和Al之间的共价键强度，降低了c/a，激活了许多滑移系。结果表明，添加Mn可以改善TiAl的塑性。(4)AEM分析表明，Mn和Fe是改善Ni_3Al塑性的有效合金元素，它们几乎等量地分布在Al和Ni位上。在本实验中，使用无序相校正离域效应。(5)高分辨电子显微镜（HREM）研究表明，强塑性变形法制备的亚微米晶Al-Mg合金的晶粒间存在规则或不规则排列的小平面和台阶，处于高能非平衡状态。

Intermetallics and ceramics, which are attractive as heat-resistance meterials, were examined by high-resolution electron microscopy (HREM), analytical lectron microscopy (AEM) and eneg-filtered electron microscopy (EFEM).The internal structures of the intermetallics and ceramics were controlled by various heat treatments including straining. The results obtained in this stuy are summarized as folows.(1) It was possible to obtaine a fine dispersion of Ni_2AlTi and Ni_2AlHf precipitate particles in NiAl intermetallics.There was a significant improvement of the creep strength (about 10 orders of magnitude) when compared with the NiAl without the particles. HREM revealed that the interaction between dislocations and particles is an attractive type. The threshold stress for the deformation was found to be about 270 MPa.(2) Addition of Fe to NiAl intermetallics was effective at higher stresses to ncrease the creep strength. HREM showed that subboundaries were formed in the creep deformation of NiAl with Fe, whereas no subboundaries were observed in the deformation of NiAl without Fe. It was oncluded thet the creep deformation of NiAl with Fe is the alloy type and that of NiAl without Fe is the metal type.(3) EFEM showed that addition of Mn to TiAl reduced the strength of covalent bonding between Ti and Al and lowered the c/a to activate many slip system. It was then suggested that the ductility of TiAl can be improved by an addition of Mn.(4) AEM showed that alloying elements of Mn and Fe, which are effetive to improve ductility of Ni_3Al, were located at both the Al and Ni sites in almost an equal magnitude. In this experiment, delocalization effect were corrected using disordered phases.(5) HREM showed that the grain bondaries of submicrometer-grained Al-Mg alloys produced by intense plastic straining tehnique contained a regular or irregular arrangement of facets and steps and thus were in a high energy non-equilibrium state.