HREM Study of high temperature metals and ceramics

利用高分辨电子显微镜(HREM)、分析电子显微镜(AEM)和ENEG过滤电子显微镜(EFE)对金属间化合物和陶瓷这两种耐热材料进行了研究。结果表明：(1)NiAl金属间化合物中弥散分布着Ni_2AlTi和Ni_2AlHf析出相，其蠕变强度较未添加析出相的NiAl合金有显著提高(约10个数量级)。高分辨电子显微镜显示，位错与颗粒之间的相互作用是一种吸引的类型。变形的门槛应力约为270 Mpa。(2)在NiAl金属间化合物中添加Fe可以在较高应力下有效地提高蠕变强度。高分辨电子显微镜分析表明，添加Fe的NiAl合金在蠕变变形过程中形成了亚晶界，而不含Fe的NiAl合金在蠕变变形过程中没有观察到亚晶界。结果表明，含Fe的NiAl为合金型蠕变变形，而不含Fe的NiAl为金属型蠕变变形。(3)有限元分析表明，添加Mn降低了TiAl与Ti之间的共价键强度，降低了c/a，激活了多个滑移系统。(4)AEM分析表明，对提高Ni_3Al塑性有重要作用的合金化元素Mn和Fe几乎等比例地分布在Al和Ni位上。实验中利用无序相修正了离域效应。(5)高分辨电子显微镜分析表明，采用强塑性应变技术制备的亚微晶Al-Mg合金的晶界具有规则或不规则的小面和台阶排列，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.