An analysis of interdiffusion in finite-geometry,two-phase diffusion couples in the Ni−W and Ag−Cu systems

The progress of homogenization in finite, multilayer diffusion couples was studied experimentally using both quantitative metallography to measure phase thicknesses and electron microprobe analysis to determine concentration-distance profiles. Ni?W couples having mean compositions in the nickel-rich terminal solid solution range (12.1 and 15.2 at. pct W) were studied after 4.43 to 240.7 hr interdiffusion treatments at 1156° and 1207°C. Ag?Cu couples having mean compositions in both of the terminal solid solution ranges (8.5 at. pct Cu and 2.1 at. pct Ag) were studied after 3.8 to 65.4 hr interdiffusion treatments at 760°C. Experimental data were in good agreement with calculations of interdiffusion based on equilibrium interface concentrations and concentration-independent interdiffusion coefficients. The good agreement between experimental data and calculated values for the Ni?W couples extended to times necessary for the achievement of essentially complete homogenization,i.e., through both the two-phase dissolution process and the subsequent stage of gradient elimination in the terminal solid solution phase.