MICROSTRUCTURAL STUDY OF THE Ni-In SUPERSATURATED SOLID SOLUTIONS OBTAINED WITH MECHONOCHEMICAL ALLOING

S.V.Tsybulya, S.V.Cherepanova, G.N.Kryukova, T.F.Grigorieva

¹ Boreskov Institute of Catalysis, pr.Lavrentieva 5, Novosibirsk, 630090 Russia
² Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, 630090 Russia
: tsybulya@catalysis.nsk.su

Keywords: solid solution, microstructure

As a rule, metastable solid solution of metals are characterized by strongly disordered crystal structure. Samples of 20%wt In in 80%wt Ni have been synthesized by mechanochemical alloing. According to TEM analysis, particle size of the alloy is over 100 nm, whereas the effective particle size calculated with a halfwidth of the 1.1.1. X-ray diffraction peak is equal to 8 nm. This does not mean that particles of the alloy consist of microblocks. High resolution electron microscopy (HREM) revealed high concentration of microstrains and stacking faults in the structure In-Ni aggregates, but did not visualize the developed micrograined boundaries. At the same time, X-ray diffraction pattern of this system may be well descriebed (with R-factor equal 6%) on the basis of the model of microcrystallite of small size (about 10 nm) possesing definite concentration of the stacking faults and microstrains of second type. In our case the effective particle size does not fit with the physical size of the particle or that of micrograin, but represents a parameter of the long-range order. This parameter is responsible for the mean distance in the crystal at which the coherence of the X-ray scattering preserves. Interesting that in the system under study long-range order into 00L direction of the close packing is better than that of HK0 direction . Best fitting is realized by using a model of the particle having the anizotropic sizes.

The model diffraction patterns were calculated using program [1]. In this program the structure of crystals of distorted close packing can be simulated by the sequence of biperiodic layers with randomly distributed stacking faults and microstrains. Number of layers, their longitudinal size, density of stacking faults and standard deviations in Gaussian distribution of interlayer translations (that characterize the microstrains) are the variable parameters of the model.

1. Cherepanova S.V., Tsybulya S.V. A new program for full profile analysis of imperfect crystals. 5 European Powder Diffraction Conference -EPDIC-5, Parma, Italy, May 25-28, 1997, p.60.