The present work deals with the characterization of the scratch resistance of two different types of coatings, i.e., chromium nitride (CrN) and diamond-like carbon prepared on X42Cr13/W (1.2083) plastic mold tool steel by physical vapor deposition and plasma-enhanced chemical vapor deposition, respectively. Our study focuses on the influence of the duplex treatment, i.e., plasma nitriding + ceramic coating on the scratch resistance of the tool steel. An advanced 3D scratch testing methodology has been used to investigate the coating adhesion and damage mechanism during scratching. The scratch analysis is completed by ball cratering test and micro-Vickers test to determine the thickness and hardness of the coatings. The test results demonstrate that the applied duplex treatment is an unambiguously advantageous surface technological process which manifests itself in higher loadability and lower sensitivity for cracking of the duplex coatings, increasing the critical forces. The scratch resistance of the combined substrate/coating material system is enhanced by the harder substrate material, providing a better interfacial bonding for both types of the ceramic coatings without changing the basic damage mechanisms.

CrN coatings are widely used in the industry due to their excellent mechanical features and outstanding wear and corrosion resistance. Using scratch and ball-on-disk wear tests, the current study deals with the tribological characterisation of CrN coatings deposited onto an X42Cr13 plastic mould tool steel. Two surface conditions of the secondary-hardened substrate are compared—the plasma nitrided (duplex treated) and the un-nitrided (simply coated) states. The appropriate combination of secondary hardening providing the maximum toughness and the high-temperature nitriding of this high Cr steel is a great challenge due to the nitrogen-diffusion-inhibiting effect of Cr. The beneficial effect of the applied duplex treatment is proven by the 34% improvement of the adhesion strength and the 43% lower wear rate of the investigated duplex coatings. Detailed morphological analyses give insight into the characteristic damage mechanisms controlling the coating failure processes during scratching and wearing. For the simply CrN-coated sample, a new type of scratch damage mechanism, named “SAS-wings”, is identified, providing useful information in predicting the final failure of the coating. The tribological results obtained on tribosystems with the investigated high Cr steel/CrN constituents represent a novelty in the given field.

Tribological investigations are of great importance, especially in the case of novel combinations of materials used for the tribosystem. In the current research, multilayer diamond-like carbon coating deposited by plasma enhanced chemical vapour deposition on an X42Cr13 plastic mould tool steel is studied with two different surface conditions of the substrate. On the one hand, it is secondary hardened; on the other hand, it is additively plasma nitrided preceding the diamond-like carbon coating. This latter combined treatment, called duplex treatment, has an increasingly wide range of applications today. However, its effectiveness largely depends on applying the appropriate nitriding technology. The tribological behaviour was characterised by an instrumented scratch test and a reciprocating ball-on-plate wear test. The results demonstrate better scratch resistance for the duplex-treated samples, while they show weaker performance in the applied wear type of loading. The current comparative study reveals the reason for the unexpected behaviour and highlights some critical aspects of the heat treatment procedure. The architecture of the tested multilayer DLC coating is unique, and no tribological results have yet been published on tribosystems combined with an X42Cr13 steel substrate. The presented results may particularly interest tribologists and the materials research community.

The primary objective of this research is to simplify and make the industrial manufacturing process of coated maraging steels more economical by combining the advantages of additive manufacturing with simultaneous bulk (aging) and surface (nitriding) treatment in an effective manner. With this aim, preliminary experiments were performed that demonstrated the hardness (and related microstructure) of an as-built MS1 maraging steel, produced by selective laser melting (SLM), is comparable to that of the bulk maraging steel products treated by conventional solution annealing. The direct aging of the solution-annealed and as-built 3D printed maraging steel resulted in similar hardness, indicating that the kinetics of the precipitation hardening process are identical for the steel in both conditions. This assumption was strengthened by a thermodynamic analysis of the kinetics and determination of the activation energy for precipitation hardening using Differential Scanning Calorimetry (DSC) measurements. Industrial target experiments were performed on duplex-coated SLM-printed MS1 steel specimens, which were simultaneously aged and salt-bath nitrided, followed by PVD coating with three different ceramic layers: DLC, CrN, and TiN. For reference, similar duplex-coated samples were used, featuring a bulk Böhler W720 maraging steel substrate that was solution annealed, precipitation hardened, and salt-bath nitrided in separate steps, following conventional procedures. The technological parameters (temperature and time) of the simultaneous nitriding and aging process were optimized by modeling the phase transformations of the entire heat treatment procedure using DSC measurements. A comparison was made based on the in-depth hardness profile estimated by the so-called expanding cavity model (ECM), demonstrating that the hardness of the surface layer of the coated composite material systems is determined solely by the type of the coatings and does not influenced by the type of the applied substrate materials (bulk or 3D printed) or its heat treatment (whether it is a conventional, multi-step treatment or a simultaneous nitriding + aging process). Based on the research work, a proposal is suggested for modernizing and improving the cost-effectiveness of producing aged, duplex-treated, wear-resistant ceramic-coated maraging steel.

Polycrystalline diamond (PCD) coatings are widely used in tribological applications, yet their scratch behaviour remains difficult to interpret due to the limitations of conventional Rockwell-C stylus testing, which is prone to premature tool failure. This study employs progressive-loading scratch tests with a hardened steel ball stylus on PCD coatings with different surface roughnesses deposited on steel substrates. Detailed 2D–3D profilometry revealed that the scratching response is strongly influenced by surface microgeometry. Examining the steel ball counterbodies provided insight into the contact evolution, indicating a gradual transition from ploughing-dominated interaction to increasingly rolling-dominated load transfer. Optical microscopy, SEM, and micro-Raman mapping revealed local stress redistribution without significant coating damage. The results demonstrate that reliable interpretation of scratch tests on ultra-hard coatings requires a combined analytical approach integrating surface topography, contact mechanics, and stress evolution. The observed behaviour suggests a progressive shift from distributed deformation to increasingly localised asperity-controlled contact.