Development of microstructural observation technique for lessductile materials deformed in tension

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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.