X-ray diffraction line profile analysis of diffusional homogenization in powder blends

Abstract

A new nondestructive method — based on computer simulation of X-ray diffraction line profiles — is proposed to characterize homogenization in compacted binary powder blends. As a parameter to characterize the stage of homogenization the relative peak position is proposed. This parameter is easy to determine in practice: during homogenization the position of an X-ray diffraction maximum is traced. As compared to other methods the present one has the following advantages: (i) it is fast and simple and (ii) it allows a more severe test of the model of interdiffusion applied. Experiments were performed with compacted blends of copper and nickel powders at 800, 900 and 1000° C. At the start of homogenization diffusion was very fast. Experiments at lower temperatures revealed that this was due to surface diffusion at the contact places between the copper and nickel particles with an activation energy of about 12 kcal mol⁻¹. Because of the sensitivity of the relative peak position to the interdiffusion model adopted it was shown that the generally accepted concentric sphere model: nucleus of nickel and shell of copper, should be modified to include a pre-alloyed shell at the copper/nickel interface at t=0. Then good correspondence between theory and experiment is obtained. Finally it was found that in the temperature range applied one diffusion mechanism is dominant with an activation energy of 32 kcal mol⁻¹, indicating grain boundary diffusion.