Mechanical and Surface Characterization of Stainless-Steel Nitride Thin Films Deposited at Different Substrate Temperatures

Stainless-steel nitride thin films were deposited onto silicon substrates at different temperatures ranging from 150 to 600 °C using reactive magnetron sputtering. The influence of substrate temperature on nitrogen incorporation, surface roughness, microstructure, and mechanical properties was systematically investigated. X-ray photoelectron spectroscopy (XPS) analysis showed that the nitrogen content increased with substrate temperature, reaching a maximum value of 34 wt.% at 350 °C, while at higher substrate temperatures (450–600 °C), the nitrogen content decreased. X-ray diffraction analysis revealed that the coating structure strongly depends on the substrate temperature. At temperatures above 450 °C, the films comprise a multiphase structure consisting of CrN, bcc-Fe, and Ni. In contrast, films deposited below 450 °C are dominated by the S-phase, corresponding to a nitrogen-supersaturated fcc structure. Scanning electron microscopy (SEM) analyses confirmed microstructural evolution with substrate temperature, showing fine, compact grains at lower temperatures and coarser structures at higher temperatures. Surface roughness measured by a profilometer exhibited a minimum at 350 °C. The mechanical performance of the films was evaluated using micro-Knoop hardness measurements, together with the calculated elastic strain indicator (H/E) and resistance to the plastic deformation parameter (H3/E2). The results showed that hardness and these mechanical indicators reached their maximum values at a substrate temperature of 350 °C. These findings provide valuable insight into the deposition–structure–property relationships of stainless-steel nitride thin films for wear-resistant and protective coating applications.