The service life of components with metallic or ceramic overlay coatings directly depends on a number of their mechanical and physical properties. For parts operating in friction assemblies, the strength of the applied coatings – closely linked to their hardness – is of particular importance. This study presents an analysis of hardness variation across the cross‑section of the coatings and substrate materials. A comparison is made between heat‑treated samples and their untreated counterparts, highlighting notable differences in hardness. The susceptibility to failure of low‑ and medium‑entropy coatings applied via plasma spraying onto cast irons, copper alloys, and composite materials is examined. The work also demonstrates the potential for optimizing the substrate to enhance coating performance.