  Estimating the diffusion coefficients experimentally in a four-component
inhomogeneous alloy following the conventional diffusion couple method by
intersecting three couples at the same composition is difficult unless a small
composition range of constant diffusivity is identified. Additionally, the
intrinsic diffusion coefficients of the components cannot be estimated in a
system with more than two components. To solve these issues, we have followed
the pseudo-binary and pseudo-ternary diffusion couple methods for estimating
the diffusion coefficients at the equiatomic composition of NiCoFeCr medium
entropy alloy. Along with the pseudo-binary interdiffusion coefficients, we
have estimated the intrinsic diffusion coefficients of all the components by
designing the pseudo-binary couples such that Ni and Co develop the diffusion
profiles keeping Fe and Cr constant in one couple and Fe and Cr develop the
diffusion profiles keeping Ni and Co constant in another couple. Subsequently,
we have proposed the relations for calculating the tracer diffusion
coefficients utilizing the thermodynamic details. We have found a good match
with the data estimated directly following the radiotracer method at the
equiatomic composition. Following, we have produced three pseudo-ternary
diffusion couples intersecting at the compositions close to the equiatomic
composition. The main pseudo-ternary interdiffusion coefficients of Fe are
found to be higher than Ni and Co. Therefore, we have estimated different types
of diffusion coefficients highlighting the complex diffusion process in the
four-component NiCoFeCr medium entropy alloy.
