The Square Root Diffusivity

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9401044 Morral The goal of this program is to model complex diffusional processes with simple equations that are based on rigorous, fundamental principles. Equations have already been derived for single and selected multiphase systems in terms of the "square root diffusivity," a kinetic property of materials. The equations have value to students who are learning how complex alloys differ from binary alloys and to engineers working on alloy and process design. The equations show how to measure the square root diffusivity of complex alloys, how to minimize interdiffusion rates and Kirkendall porosity, and how to vary the phases that form in interdiffusion zones. An experimental program combining electron microprobe and image analysis of nickel-base superalloys is being used to test the accuracy of the equations and to uncover new principles related to diffusion in multicomponent, multiphase systems. %%% Diffusion causes property degradation in coated turbine blades, metal-matrix composites, and other materials used for high temperature service. In addition, diffusion is important during high temperature processing, for example, pack cementation, carburizing and annealing. ***