This work presents the results of deposition by magnetron sputtering nanostructured multilayer Cr/(Cr/a-C)ml coatings on AISI 316L and AISI 321 steel substrates. Chemical compositions were confirmed through EDX analysis with scanning electron microscopy. The coating thickness was measured with Calotester (KaloMAX II) and the total thickness of the coatings obtained ranged from 1.684 ± 0.193 μm for AISI 316L to 1.749 ± 0.123 μm for AISI 321. A Daimler-Benz Rockwell indentation test for adhesion quality and a nanoindentation test with a Berkovich indenter were carried out. According to the Raman spectroscopy analysis and in agreement with mechanical tests, it is supposed that it is the formation of a diamond-like carbon phase which enhances the mechanical properties. The hardness values obtained for the nanostructured multilayer Cr/(Cr/a-C)ml coatings were improved compared to those of the base stainless steels.

A chromium/amorphous carbon (Cr/(Cr/a-C)ml) nanostructured multilayer coating with a chromium sublayer was deposited on 42CrMo4 (1.7225,BDS EN ISO 683-2:2018), 100Cr6 (1.3505, BDS EN ISO 683-17:2024), and HS18-0-1 (1.3355, BDS EN ISO 4957:2018) alloy steels, selected for their use in contact-loaded components subjected to cyclic fatigue and intense wear. The coating was sputter deposited by MF pulsed magnetron sputtering under consistent process parameters. The resulting coating, approximately 1.8 μm thick, can significantly enhance the service life of these components. Adhesion was evaluated via the Daimler–Benz test, while coating homogeneity was confirmed through energy-dispersive spectroscopy, revealing a consistent chemical composition across sample surfaces. Raman spectroscopy indicated a high sp³/sp² ratio, confirming a dominant diamond-like carbon structure. Nanoindentation measurements verified the coating’s hardness, aligning with the observed structural properties. These results validate the process parameters for depositing a Cr/(Cr/a-C)ml coating on these alloy steels, achieving this study’s objectives.

Test specimens fabricated from 42CrMo4 steel were subjected to heat treatment comprising quenching followed by high-temperature tempering. This treatment is commonly referred to as hardening, and the result is a tempered sorbite microstructure that provides a balanced combination of strength and plasticity. In order to improve the hardness and wear resistance of the contact surfaces, two types of physical vapor deposition (PVD) coatings were deposited onto the specimens: the first was a two-component architecture Cr/CrTiAl and the second was a multilayer Cr/(CrTiAl)N/CrTiAl. In both configurations, an intermediate chromium adhesion layer was initially deposited to enhance interfacial bonding with the substrate. The adhesion strength of the deposited coatings to the steel substrates was evaluated using a standardized adhesion test. The adhesion quality was classified as HF1 (the highest adhesion class in the HF1–HF6 scale, defined in EN ISO 26443), indicating excellent interfacial bonding. The hardness and modulus of elasticity of both coatings were determined through nanoindentation. According to the measured hardness values of the two coatings, 27.3 GPa (Cr/CrTiAl) and 37.5 GPa (Cr/(CrTiAl)N/CrTiAl), they can be classified as hard coatings (hardness greater than 20 GPa). Despite the difference in hardness, the two coatings have comparable elastic modulus values: Eit = 353 GPa for the two-component architecture coating and Eit = 349 GPa for the three-component architecture coating. Tribological characterization was performed using the ball-on-disc method under dry sliding conditions over a total sliding distance of 59 m, whereby the friction coefficient (µ) was recorded. Additionally, the wear rate of the applied coatings was calculated from the measured wear volumes or profiles. The two coatings have comparable friction coefficient values (Cr/CrTiAl–μ = 0.362, Cr/(CrTiAl)N/CrTiAl–μ = 0.325), but the three-component architecture coating Cr/(CrTiAl)N/CrTiAl has a lower wear rate (k = 1.64 × 10⁻⁴) compared to the two-component architecture coating Cr/CrTiAl, which has a wear rate of k = 7.6 × 10⁻⁴. The investigated coatings have hardness, modulus of elasticity and friction coefficient values competitive with those of nitride coatings (two-component architecture and three-component architecture), and their wear rate also corresponds to generally accepted values.

The aim of this work is to investigate the possibility of improving the performance properties of 40CrMnMo7 steel by conducting duplex surface modification treatment. Chemical-thermal treatment processes were used—nitrocarburization and ion-nitriding and subsequent application of a nanostructured multilayer coating, Cr/(Cr-C)ml. The resulting structures and their influence on the adhesion of the applied coating, as well as their influence on the tribological properties of the coating, were studied. By conducting Glow Discharge Optical Emission Spectroscopy (GDOES), it was established that the penetration of nitrogen into the depth is greater in the ion-nitriding process, and the results of the conducted optical metallography and hardness measurement show that after ion-nitriding, the obtained hard layer has a greater thickness and hardness. The data obtained from the studies of the phase composition of the hard layers show that after nitrocarburization the non-stoichiometric, but crystalline phase Fe₃N_1.1 (ξ)—98.4% was formed. In the composition of the hard layer formed after the ion-nitriding process, the presence of Fe₃N (ξ-phase) in an amount of 79.5% and Fe₄N (γ′-phase) in an amount of 19.1% was established. On the chemically and thermally treated surfaces, a Cr/(Cr-C)ml coating was applied through the unbalanced magnetron sputtering technology. The applied coating has a hardness of 17.1 ± 0.6 GPa and a modulus of elasticity of 289 ± 8.7 GPa. The thickness of the coating applied on the test bodies not subjected to diffusion enrichment is 1.967 µm, and the adhesion class is classified as HF-2. It has been established that the profile of the surfaces obtained after the application of the chemical-thermal treatment processes has an impact on the thickness of the applied coating and on its adhesion. After nitrocarburization, the thickness of the coating is 2.9 µm, and the adhesion of the coating is classified as HF-0. The thickness of the applied coating on the test bodies subjected to ion-nitriding is 2.4 µm, and the adhesion class is HF-1. The results of the conducted tribological tests show that the used chemical-thermal treatment processes have an impact on the coefficients of friction and wear of the coating. The coefficient of friction for the combination of the nitriding process and Cr/(Cr-C)ml coating has the highest value (µ ≈ 0.38), while that of the ion-nitrided sample with subsequent coating has a value (µ ≈ 0.21) slightly higher than the COF of the test body with only the coating applied (µ ≈ 0.18). The lowest value of the coating wear coefficient is registered for the combination of the ion-nitriding and coating process (k = 7.96 × 10⁻⁵), while for the combination of nitriding and coating, it is the highest (k = 12.4 × 10⁻⁴). The relevance of the present work is related to the implementation of surface modification of 40CrMnMo7 steel by using established technological processes of chemical-thermal treatment and subsequent deposition of nanostructured multilayer Cr/(Cr-C)ml coating. The other novelty in the present study is related to the use of MF pulsed DC power supplies, operating at a fixed frequency of 100 kHz and a specific pulse shape, similar to the shape of HiPIMS pulses, for the deposition of nanostructured multilayer Cr/(Cr/a-C)ml coatings.

The effect of nanosecond laser modification on X165CrMoV12 tool steel before and after heat treatment was investigated. Three laser texturing modes were applied to the studied material, with the variables being the frequency used and the pulse energy: 50 kHz/pulse energy 0.9 mJ, 100 kHz/pulse energy 0.45 mJ, and 150 kHz/pulse energy 0.3 mJ. The other parameters of laser texturing were power—90%; speed—500 mm/s; hatching angle—0° (horizontal), +60°/−60° (or equivalent 120°), and +30°/−30° (or equivalent 150°); and Hatching Distance—0.02 mm. The surface laser modification process aims to obtain a homogeneous and adaptive surface relief optimizing the operational properties of the working surfaces of the parts under dry contact friction conditions. The influence of the used laser modification modes on the roughness class of the obtained surfaces, the structure of the formed modified surface and the friction coefficient was studied. The comparative analysis showed that the lowest roughness class (Ra—4.123 µm) was obtained when using an operating frequency of 50 kHz. The obtained friction coefficient values were lowest in the following sequence of processes: laser texturing and subsequent thermal treatment. The lowest friction coefficient (µ = 0.0041) was registered in the test bodies processed with a mode in which the operating frequency was 50 kHz and the pulse energy was 0.9 mJ, after which they were subjected to thermal treatment according to the used cycle. In this processing sequence, no diffusion-related defects (decarburization) were observed on the surface layer of the tested steel.

Magnetron-sputtered coatings consisting of multiple alternating layers of chromium and amorphous carbon (Cr/a-C)ml were deposited on HS6-5-2 steel with an intermediate chromium layer by varying deposition rates. Three series of coatings, S1, S2, and S3, with thicknesses of 1.74, 1.15, and 1.14 μm and average chromium contents of 89.3, 66.0, and 59.7 wt.% Cr, respectively, were obtained. Open-circuit potential, cyclic potentiodynamic measurements, and electrochemical impedance spectroscopy were used to characterize their corrosion resistance in 3.5% NaCl. The surfaces were observed with optical and scanning electron microscopy before and after the corrosion tests, and changes in the elemental composition were monitored by energy-dispersive spectroscopy. The protective properties of coatings from series S2 and S3 are similar and significantly better than those of S1. They are characterized by a corrosion current below 1 μA cm^–2 and a stable passive state up to over 0.9 V_Ag/AgCl. The coatings have cathodic behavior towards the substrate, and when the coatings are damaged, galvanic corrosion causes deep pits. Coatings deposited at lower rates and with higher carbon content demonstrate significantly enhanced corrosion resistance in 3.5% NaCl. All three series of Cr/(Cr/a-C)ml@HS6-5-2 exhibit identical corrosion behavior after compromising the coatings’ integrity.