Elasticity and Unelasticity of Intermetallic Compounds

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1. The Rectangular Parallelepiped Resonance (RPR) method has been known to be a powerful method for determining the elastic constants, but the amount of numerical calculations for the data analysis is quite large. A new method of analysis is proposed, which is applicable to the case of specimens of cubic crystals. In this method, the resonance frequencies are calculated and stored for various combinations of Poisson's ratio, nu and anisotropy factor. A. The measured spectrum of resonance frequencies is compared in turn with the calculated spectra by a procedure of something like pattern comparison so as to determine roughly the values of elastic constants. Final refinements can be done successfully by the interpolation of the stored data.2. The three elastic stiffness constants of various Ni-based intermetallic compounds Ni_3X (X=Mn, Fe, Al, Ga, Ge and Si) with L1_2 structure have been determined at room temperature by the rectangular parallelepiped resonance method. The elastic anisotropy factor, A, of the compounds is ge nerally large, ranging from 2.5 to 3.3, except for Ni_3Ge(A=1.71). The elastic constants exhibit some correlation with the lattice constants. The minor element, X, can be regarded as exerting "chemical pressure" which causes the expansion of the Ni lattice, thus resulting in the decreaseof the elastic constants.3. The self-diffusion coefficients of both the constituents (D _<Ni> and D_<Ge> in Ni_3Ge) have been first measured for L1_2 compounds. The relation of the self-diffusivities in the temperature range from 1173 to 1273 K is given as follows : 22< D _<Ni>/D_<Ge><29, where D is self-diffusion coefficient.