Multicomponent diffusion in ternary and quaternary diffusion couples and in multilayered assemblies

Two main objectives of this research were to determine diffusional interactions among various components in ternary Cu-Ni-Zn and quaternary Cu-Ni-Zn-Mn alloys and to study evolution of concentration profiles and diffusion paths in multilayered structures. Diffusion couples were assembled with alpha-phase (FCC) Cu-Ni-Zn alloys and annealed at 775°C. The annealed couples were analyzed for concentration profiles by electron probe microanalysis and interdiffusion fluxes and interdiffusion coefficients were determined over selected composition ranges by Dayananda-Sohn analysis. The interdiffusion analysis was carried out by using a computer program, MultiDiflux, developed by Dayananda and Ram-Mohan. In the Cu-Ni-Zn couples, interdiffusion fluxes of Ni and Cu were observed to be enhanced up the concentration gradient of Zn.;Applicability of the MultiDiflux program for the interdiffusion analysis of quaternary diffusion couples was assessed with the aid of a test couple characterized by an arbitrarily selected set of constant quaternary interdiffusion coefficients. The MultiDiflux program was also utilized for the determination of quaternary interdiffusion coefficients from profiles of two experimental Cu-Ni-Zn-Mn diffusion couples investigated at 775°C. The quaternary interdiffusion coefficients evaluated over selected composition ranges from the test as well as the experimental Cu-Ni-Zn-Mn couples were checked for their acceptability by regenerating the concentration profiles from error function solutions for n-component diffusion couples derived by Ram-Mohan and Dayananda through a transfer matrix method (TMM). The TMM methodology was implemented in the MultiDiflux program and used successfully for all the quaternary couples. In the Cu-Ni-Zn-Mn couples, the interdiffusion flux of Ni was enhanced up the concentration gradients of Mn and the interdiffusion flux of Cu increased up the gradient of Zn. Also, the main interdiffusion coefficients of Zn and Mn were observed to be one order of magnitude larger than that of Ni.;Analytical expressions were developed for spatial and temporal evolution of concentration profiles in single-phase multicomponent multilayered diffusion assemblies (MDAs) assembled with a number of finite alloy-layers of various compositions sandwiched between two bulk terminal alloys. The expressions were successfully used for the prediction of concentration profiles in an experimental Cu-Ni-Zn MDA assembled with a single sandwiched layer and annealed at 775°C. The analytical expressions were also used to simulate evolution of concentration profiles and diffusion paths for a ternary MDA containing a single finite middle layer as a function of layer thickness (h) and time (t). The diffusion path of such an MDA varies with time and each path configuration is associated with a unique h/ t ratio. Diffusional interactions among components may lead to either depletion or accumulation of individual components in the middle layer of an MDA.;The MultiDiflux program was also employed for the determination of ternary interdiffusion coefficients for the (beta) Ni-Ru-Al alloys from diffusion couple assembled with NiAl and RuAl disks and annealed at 1100°C.