Search Results (20)

The article discusses the phenomena and destructive mechanisms occurring on the surface of 1.2344 steel dies used during the hot forging of disc-type forgings. Preliminary research has shown that gas nitriding alone, used so far, is insufficient due to the occurrence of destructive mechanisms other than abrasive wear, such as thermal and thermomechanical fatigue, which cause the average durability of such tools to be approximately 5000 forgings. Analyses were also carried out to assess the load on forging tools using numerical modeling (Forge 3.0NxT), which confirmed the occurrence of large and cyclically changing thermal and mechanical loads during the forging process. Therefore, in order to increase operational durability, it was decided to use two types of hybrid layers, differing in the PVD coating used: TiCrAlN and CrN, and then subjected to gas nitriding (GN). The obtained results showed that, depending on the area of the tool and the current working conditions, the applied PVD coatings protect the surface layer of the tool against the dominant destructive mechanisms. In both cases, the strength increased to the level of 7000 forgings, the tools could continue to work, and globally, slightly better results were obtained for the GN+TiCrAlN layer. The CrN-type layer protects the tool more against thermal fatigue, while the TiCrAlN layer is more resistant to abrasive wear. In areas where the hybrid layer was worn, a decrease in hardness was observed from 1300 HV to 600–700 HV, and in places of intense material flow (front—point 2 and tool bridge—point 9) the hardness dropped to below 400 HV, which may indicate local tempering of the material. Moreover, the research has shown that each process and tool should be analyzed individually, and the areas in the tool where particular destructive mechanisms dominate should be identified, so as to further protect the forging tool by using appropriate protective coatings in these areas. Full article

CrAlTiN-Si coatings have demonstrated their ability to prolong the operational life and improve the performance of cutting tools, primarily attributable to their exceptional mechanical, thermal, and tribological properties. Consequently, this investigation focused on the deposition of CrAlTiN-Si coatings utilizing the high-power impulse magnetron sputtering (HiPIMS) technique. The chemical composition, morphology, and microstructure of these coatings, as well as their mechanical and tribological properties, were investigated. The obtained results revealed that the incorporation of silicon into the CrAlTiN matrix significantly influenced the chemical composition, microstructure, and mechanical properties of the coatings. Specifically, silicon contents ranging from 0 to 1.0 at.% led to the formation of a face-centered cubic (fcc) solid solution within the coatings, resulting in a reduction in the lattice parameter from 0.412 nm to 0.409 nm. However, when the silicon content reached 1.9 at.%, a nanocomposite phase comprising an fcc solid solution of CrAlTiSiN and an amorphous phase of SiNx was observed, along with an increase in the lattice parameter from 0.409 nm to 0.413 nm. An XPS analysis confirmed the presence of oxides in all the coatings, but only the sample with a silicon content of 1.9 at.% showed the presence of Si-N bonds. Furthermore, all the coatings exhibited a distinctive cauliflower-type morphology. The nano-hardness testing demonstrated that the incorporation of silicon resulted in coatings with high nano-hardness values, from 20.0 GPa for the sample without silicon to 22.2 GPa when the silicon content was 1.9 at.%. Moreover, as the Si content increased, the presence of silicon contributed to enhancements in the toughness and fracture resistance of the coating. Full article

(CrMoNbTaZr)N_X coatings were deposited on Si (100) by magnetron sputtering under various N₂/(Ar+N₂) flow ratios. An X-ray diffractometer, transmission electron microscopy, scanning electron microscopy and atomic force microscopy were used to characterize the crystallinity and microstructure of the films. The elemental composition was characterized by energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The hardness and friction coefficient were respectively determined by nanoindentation and nanoscratch. The sheet resistance was studied using a four-point probe. The results suggest that the crystallinity is strongly influenced by the nitrogen content in the films. The chemical stoichiometry of nitride determines the evolutions of the microstructure, mechanical properties and resistivity. Correlations between the microstructure and the properties of the (CrMoNbTaZr)N_X films were studied. Full article

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. Full article

CrN_x coatings with a low nitrogen content below 31.7 at.% were deposited using closed field unbalanced magnetron sputtering by varying the N₂:Ar flow ratio. A dense and column-free CrN_x coating was obtained at a nitrogen content of 14.8 at.%, whereas the other CrN_x coating were all columnar structured. The column-free CrN_x coating was composed of two types of structures: an N-incorporated Cr(N) solid solution matrix with a high number of point defects and a Cr(N) matrix with dispersed Cr₂N nanocrystallines. The pinning effect of Cr₂N nanocrystallines and point defects in Cr(N) grains are responsible for the formation of a column-free CrN_x coating. The columnar-free CrN_x coating exhibits a high hardness of 33.7 GPa, which is comparable to the hardness of Cr₂N coating but 2.6 times larger than that of the Cr coating. It also has significantly better corrosion resistance than both Cr and Cr₂N coating, with a corrosion current density of 4.1 × 1.0⁻⁹ A/cm² that was only 1/20 than that of Cr coating. Full article

The paper’s aim is the assessment of corrosion behaviour of a CrN_x-coated 310 H stainless steel under simulated supercritical water conditions (550 °C and 25 MPa) for up to 2160 h. The CrN_x coating was obtained by the thermionic vacuum arc (TVA) method. The oxides grown on this coating were characterized using metallographic and gravimetric analysis, SEM with EDS, and grazing incidence X-ray diffraction (GIXRD). A diffusion mechanism drives oxidation kinetics because it follows a parabolic law. By XRD analysis, the presence of Cr₂O₃ and Fe₃O₄ on the surface of the autoclaved CrN_x-coated 310 H samples were highlighted. Corrosion susceptibility assessment was performed by electrochemical impedance spectroscopy (EIS) and linear potentiodynamic polarization. EIS impedance spectra show the presence of two capacitive semicircles in the Nyquist diagram, highlighting both the presence of the CrN_x coating and the oxide film formed during autoclaving on the 310 H stainless steel. Very low corrosion rates, with values up to 11 nm × year⁻¹, obtained in the case of autoclaved for 2160 h, CrN_x-coated samples indicated that the oxides formed on these samples are protective and provide better corrosion resistance. The determination of micro hardness Vickers completed the above investigation. Full article

The high-power impulse magnetron sputtering (HiPIMS) technique was applied to deposit multilayer-like (Cr, Y)N_x coatings on AISI 304L stainless steel, using pendular substrate oscillation and a Cr-Y target and varying the nitrogen flow rate from 10 to 50 sccm. The microstructure, mechanical and tribological properties were investigated by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, instrumented nano-hardness, and wear tests. The columnar grain structure became highly segmented and nanosized due to pendular substrate oscillation and the addition of yttrium. The deposition rate increased continuously with the growing nitrogen flow rate. The increase in nitrogen flow from 10 to 50 sccm increased the hardness of the coatings (Cr, Y)N_x, with a maximum hardness value of 32.7 GPa for the coating (Cr, Y)N_x with a nitrogen flow of 50 sccm, which greatly surpasses the hardness of CrN films with multilayer-like (Cr, Y)N_x coatings architecture. The best mechanical and tribological performance was achieved for a nitrogen flow rate of 50 sccm. This was enabled by more elevated compressive stresses and impact energies of the impinging ions during film growth, owing to an increase of HiPIMS peak voltage with a rising N2/Ar ratio. Full article

Friction and wear resistance are important factors that affect the selection of accident-tolerant fuel coating materials. In this study, the wear behavior of a series of Cr-N_x coatings with different N contents was investigated using a reciprocating sliding tester. The coating morphology, change in the coefficient of friction during the friction and wear tests, and wear volume after the friction and wear tests, were characterized and discussed in detail. The results show that the Cr₂N coating has better anti-friction and wear resistance behaviors than the Cr and CrN coatings under anhydrous and aqueous conditions. In addition, the water environment promoted the wear of the Zr-4 alloy and Cr coatings and inhibited the wear of the CrN and Cr₂N coatings. The mechanisms of friction and wear were also discussed. Full article

Ceramic coatings deposited on orthopedic implants are an alternative to achieve and maintain high wear resistance of the metallic device, and simultaneously allow for a reduction in metal ion release. Silicon nitride based (SiN_x) coatings deposited by high power impulse magnetron sputtering (HiPIMS) have shown potential for use in joint replacements, as a result of an improved chemical stability in combination with a good adhesion. This study investigated the effect of N, C, Cr, and Nb content on the tribocorrosive performance of 3.7 to 8.8 µm thick SiN_x coatings deposited by HiPIMS onto CoCrMo discs. The coating composition was assessed from X-ray photoelectron spectroscopy and the surface roughness by vertical scanning interferometry. Hardness and Young’s modulus were measured by nanoindentation and coating adhesion was investigated by scratch tests. Multidirectional wear tests against ultrahigh molecular weight polyethylene pins were performed for 2 million cycles in bovine serum solution (25%) at 37 °C, at an estimated contact pressure of 2.1 MPa. Coatings with a relatively low hardness tended to fail earlier in the wear test, due to chemical reactions and eventually dissolution, accelerated by the tribological contact. In fact, while no definite correlation could be observed between coating composition (N: 42.6–55.5 at %, C: 0–25.7 at %, Cr: 0 or 12.8 at %, and Nb: 0–24.5 at %) and wear performance, it was apparent that high-purity and/or -density coatings (i.e., low oxygen content and high nitrogen content) were desirable to prevent coating and/or counter surface wear or failure. Coatings deposited with a higher energy fulfilled the target profile in terms of low surface roughness (Ra < 20 nm), adequate adhesion (L_c2 > 30 N), chemical stability over time in the tribocorrosive environment, as well as low polymer wear, presenting potential for a future application in joint bearings. Full article

CrN_x/Ag multilayer coatings and a comparative CrN_x single layer were deposited via reactive magnetron sputtering. In multilayer coatings, the thickness of each CrN_x layer was constant at 60 nm, while that of the Ag layer was adjusted from 3 to 10 nm. Microstructure of the films was characterized by X-ray diffraction and transmission electron spectroscopy. The results suggest that the film containing 3 nm of Ag layer presents a nanocomposite structure comprising fine nano-grains and quasi-amorphous clusters. With Ag layer thickness reaching 4.5 nm and above, Ag grains coalesce to produce continuous an Ag layer and exhibit (111) preferential crystallization. Hardness of the films was detected by nanoindentation and it reveals that with increasing the Ag layer thickness, the hardness continuously decreases from 30.2 to 11.6 GPa. Wear performance of the films was examined by the ball-on-disk test at 500 °C. The result suggests that the out-diffusion of Ag towards film surface contributes to the friction reduction, while the wear performance of films depends on the thickness of the Ag layer. Full article

Molds made of tool steels used in aluminum high-pressure die casting should routinely withstand tens of thousands of injection cycles, but repeated loading and temperature spikes result in their frequent premature wear. Extending their lifetime could be sought by nitriding or application of coatings of even higher hardness or both. Therefore, in the present experiment the arc-deposited Cr/(CrN)/n^x(CrN/CrAlN)/m^x(CrAlN/VN) or Cr/(CrN)/n^x(CrN/TiAlN)/m^x(TiAlN/VN) nano-multilayer stacks were deposited on glow discharge nitrided X40CrMoV5.1 steel. The scanning and transmission electron microscopy backed by Energy Dispersive X-ray Spectroscopy measurements of local chemical composition helped to confirm that the coatings are built of nanolayers of respective nitrides of period less than 10 nm. They also showed that droplets being characteristic for arc deposition method were enriched either in chromium, aluminum or vanadium but not in titanium. Both coatings presented comparable hardness of ~25 GPa, but the one covered with TiAlN/VN was roughly twice as wear resistant as the CrAlN/VN. Simultaneously, they were ~200 and ~100 more wear resistant than X40CrMoV5.1reference steel. Full article

PEMFC are considered to be the most promising for automotive energy because of their good working effect, low temperature, high efficiency, and zero pollution. Stainless steel as a PEMFC bipolar plate has unparalleled advantages in strength, cost, and processability, but it is easy to corrode in a PEMFC working environment. In order to improve the corrosion resistance, the surface modification of 316L stainless steel is a feasible solution for PEMFC bipolar plates. In the present study, the plasma-nitrided coating and CrN_x coating were prepared by the plasma-enhanced balanced magnetron sputtering technology on the 316L stainless steel surface. The microstructures, phase compositions, and corrosion resistance behavior of the coatings were investigated. The corrosion behavior of the prepared plasma-nitrided coating and CrN_x coating was investigated by potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy (EIS) in both cathodic and anodic environments. The experimental results show that corrosion resistance of the CrN_x coating was better than the plasma-nitrided coating. It was indicated that the technology process of nitriding first and then depositing Cr was better than nitriding only. Full article

In the present work, the structure, stress state and phase composition of MeN/SiN_x (Me = Zr, Cr, Al) multilayered films with the thickness of elementary layers in nanoscale range, as well as their stability to high temperature oxidation, were studied. Monolithic (reference) and multilayered films were deposited on Si substrates at the temperatures of 300 °C (ZrN/SiN_x and AlN/SiN_x systems) or 450 °C (CrN/SiN_x) by reactive magnetron sputtering. The thickness ratios of MeN to SiN_x were 5 nm/2 nm, 5 nm/5 nm, 5 nm/10 nm and 2 nm/5 nm. Transmission electron microscopy (TEM), X-ray Reflectivity (XRR) and X-ray Diffraction (XRD) testified to the uniform alternation of MeN and SiN_x layers with sharp interlayer boundaries. It was observed that MeN sublayers have a nanocrystalline structure with (001) preferred orientation at 5 nm, but are X-ray amorphous at 2 nm, while SiN_x sublayers are always X-ray amorphous. The stability of the coatings to oxidation was investigated by in situ XRD analysis (at the temperature range of 400–950 °C) along with the methods of wavelength-dispersive X-ray spectroscopy (WDS) and scanning electron microscopy (SEM) after air annealing procedure. Reference ZrN and CrN films started to oxidize at the temperatures of 550 and 700 °C, respectively, while the AlN reference film was thermally stable up to 950 °C. Compared to reference monolithic films, MeN/SiN_x multilayers have an improved oxidation resistance (onset of oxidation is shifted by more than 200 °C), and the performance is enhanced with increasing fraction of SiN_x layer thickness. Overall, CrN/SiN_x and AlN/SiN_x multilayered films are characterized by noticeably higher resistance to oxidation as compared to ZrN/SiN_x multilayers, the best performance being obtained for CrN/SiN_x and AlN/SiN_x with 5 nm/5 nm and 5 nm/10 nm periods, which remain stable at least up to 950 °C. Full article

Ceramic coatings may be applied onto metallic components of joint replacements for improved wear and corrosion resistance as well as enhanced biocompatibility, especially for metal-sensitive patients. Silicon nitride (SiN_x) coatings have recently been developed for this purpose. To achieve a high coating density, necessary to secure a long-term performance, is however challenging, especially for sputter deposited SiN_x coatings, since these coatings are insulating. This study investigates the time-dependent performance of sputter-deposited SiN_x based coatings for joint applications. SiN_x coatings with a thickness in the range of 4.3–6.0 µm were deposited by reactive high power impulse magnetron sputtering onto flat discs as well as hip heads made of CoCrMo. SiN_x compositional analysis by X-ray photoelectron spectroscopy showed N/Si ratios between 0.8 and 1.0. Immersion of the flat disks in fetal bovine serum solution over time as well as short-term wear tests against ultra-high molecular weight polyethylene (UHMWPE) discs showed that a high coating density is required to inhibit tribocorrosion. Coatings that performed best in terms of chemical stability were deposited using a higher target power and process heating. Full article

The high temperature oxidation performance of nitride thin films has become an important issue when they are used as protective coatings on dry cutting tools or on die casting molds. In this study, the high temperature oxidation behaviors of CrN_x and Cr-Si-N thin films were investigated at 1000 °C for 6 h in ambient air. The CrN_x and Cr-Si-N thin films were prepared by a bipolar asymmetric pulsed direct-current (DC) magnetron sputtering system. Cr-Si-N films with silicon content ranging from 3.9 to 12.2 at.% were deposited by adjusting the Si target power. A thermogravimeter was adopted to study the oxidation kinetics of thin films. The weight gains were measured to calculate the parabolic rate constants of thin films. X-ray diffraction, X-ray mapping, and Auger electron spectroscopy were employed to study the microstructure and elemental redistributions of oxidized thin films. The as-deposited CrN_x and Cr-Si-N thin films consisted of CrN and Cr₂N mixed phases. The faceted Cr₂O₃ surface oxides, porous inner oxide layer, and oxygen-containing CrSi₂ phases were found for the CrN film after oxidation test. On the other hand, the Cr-Si-N film containing 12.2 at.% Si showed a dense surface oxide layer and a thick and compact nitride layer, which indicates its best oxidation resistance. The high temperature oxidation resistance of Cr-Si-N thin films was improved by increasing Si content, due to the amorphous matrix contained nanocomposite microstructure and the formation of amorphous silicon oxide to retard the diffusion paths of oxygen, chromium, silicon, and nitrogen. The lowest parabolic rate constant of 1.48 × 10^–2 mg²/cm⁴/h was obtained for the 12.2 at.% Si contained Cr-Si-N thin films, which provided the best oxidation resistance at 1000 °C for 6 h in this work. It should be noted that the residual tensile stress of thin film had a detrimental effect on the adhesion property during the oxidation test. Full article