Cast Microstructure of a Complex Concentrated Noble Alloy Ag₂₀Pd₂₀Pt₂₀Cu₂₀Ni₂₀

A complex concentrated noble alloy (CCNA) of equiatomic composition (Ag₂₀Pd₂₀Pt₂₀Cu₂₀Ni₂₀-20 at. %) was studied as a potential high-performance material. The equiatomic composition was used so that this alloy could be classified in the subgroup of high-entropy alloys (HEA). The alloy was prepared by induction melting at atmospheric pressure, using high purity elements. The degree of metastability of the cast state was estimated on the basis of changes in the microstructure during annealing at high temperatures in a protective atmosphere of argon. Characterisation of the metallographically prepared samples was performed using a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Observation shows that the microstructure of the CCNA is in a very metastable state and multiphase, consisting of a continuous base of dendritic solidification-a matrix with an interdendritic region without other microstructural components and complex spheres. A model of the probable flow of metastable solidification of the studied alloy was proposed, based on the separation of L-melts into L₁ (rich in Ni) and L₂ (rich in Ag). The phenomenon of liquid phase separation in the considered CCNA is based on the monotectic reaction in the Ag-Ni system.