Structural Features of CrTiZrNbHf Ion-Plasma High-Entropy Coatings Produced by Multi-Cathode Arc Sputtering

Coatings of CrTiZrNbHf system with non-equiatomic chemical composition obtained on steel substrate by vacuum-arc triple-cathode sputtering technology have been investigated. One of the work objectives was to form a coating of equiatomic composition. However, this objective failed to be achieved through the use of various combinations of cathode composition or varying the technological parameters of sputtering. The structure of the coatings of weighted average composition of Cr0.30Ti0.35Zr0.25Nb0.08Hf0.01 was investigated using scanning electron microscopy (SEM) and X-ray spectral analysis (XRS). The analysis has indicated that the coating exhibits a homogeneous microstructure, with the coating components forming a solid solution. No evidence of intermetallic phases was detected. It has been demonstrated by XRS methods that the coating has increased internal stresses caused by atomic distortion of components and elastic atomic displacements. The lattice deformation was determined within 3–4%. Furthermore, XRS has revealed the presence of coherent scattering regions (CSRs) with sizes of up to 6 and 7 nm in the coating structure. The complex of mechanical characteristics of the coating, obtained by continuous indentation methods, has exhibited a significantly higher hardness, as well as resistance to elastic and plastic deformation, than the similar properties of the used substrate of medium-carbon steel doped with Cr, Ni, and Mo. In the final part of the work, the thermodynamic stability of the structure of solid solutions of high-entropy alloys is discussed in general and in CrTiZrNbHf coating, in particular, based on calculated criteria. The belonging of the investigated coating of non-equiatomic composition to the high-entropy alloys is substantiated.