Development of microstructural observation technique for lessductile materials deformed in tension

为了研究金属间化合物和陶瓷等韧性较差材料的拉伸变形过程中的组织演变，对双剪试验技术进行了改进，该技术可作为常规弯曲试验的简单应用。用分析电子显微镜(AEM)测量了Ni_3Al和Ni_3Ge的互扩散系数，这对评价高温力学性能是很重要的。AEM已被进一步用于定位Ni3Al、NiAl和TiAl中的代位合金元素。研究结果总结如下：1.研究成果。直径为3 mm、长度为11 mm的双剪试件可以提供与常规拉伸试件相同的力学性能。然后，可以使用双剪切测试技术来检查延性较差的材料的拉伸性能。Ni_3Al和Ni_3Ge的互扩散系数符合Arrhenius关系式：D_0=D_0exp(-Q/RT)，D_0=1.18×10~(-4)；m^2/S，Q=276kJ/mol；替代合金元素Mn和Fe几乎等密度地分布在Al和Ni位上，是提高Ni3Al塑性的有效元素。在本实验中，利用无序位相对离域效应进行了校正，同时作者还开发了校正技术。合金元素Fe与Ti合金化时更倾向于占据NiAl位，优先于Al位；而当与Pd合金化时，则更倾向于占据Al位。在这个实验中，作者发展了一个方程式，允许在多组分系统中确定站点占用率。在TiAl中添加Mn降低了Ti与Al之间的共价键强度，降低了C/a，从而激活了许多滑移系统，从而提高了TiAl的塑性。

In order to examine microstructural evolution with tensile deformation of less ductile materials such as intermetallics and ceramics, a modification has been made of double-shear testing technique which can be used as an simple application of a conventional bending test. Analytical electron microscopy (AEM) has been used to measure interdiffusion coefficients of Ni_3Al and Ni_3Ge which are important for the evaluation of mechanical properties at high temperatures. AEM has been further used to locate substitutional alloying elements in Ni_3Al, NiAl and TiAl. The results are summarized as follows.1. Double-shear specimens with 3 mm in diameter and 11 mm in length can give the same mechanical behavior as expected from conventional tensile specimens. It is then possible to examine tensile properties of less ductile materials with use of the double-shear testing technique.2. Interdiffusion coefficients of Ni_3Al and Ni_3Ge are repesented by an Arrhenius relation as D=D_0exp (-Q/RT) with D_0=1.18x10^<-4>m^2/s and Q=276 kJ/mol for Ni_3Al and D_0=9.03x10^<-5>m^2/s and Q=248 kJ/mol for Ni_3Ge.3. Substitutional alloying elements, Mn and Fe, which are effective to improve ductility of Ni_3Al, are located at both the Al and Ni sites in almost an equal maginitude. In this experiment, delocalization effects have been corrected using disordered phases, while the correction technique being developed by the authors.4. Alloying element, Fe, is more likely to occupy the Ni site in NiAl when alloyed with Ti with the preference of Al site, and to occupy the Al site when alloyed with Pd with the preference of Ni. In this experiment, the authors developed an equation which allows site occupancy determination in multi-component systems.5. Addition of Mn to TiAl reduces the strength of covalent bonding between Ti and Al and lowers the c/a to activate many slip systems so that, it has been suggested, the ductility of TiAl can be improved.