Nanolayer CrAlN/TiSiN coating designed for tribological applications

With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H³/E² being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating.     

Wear resistance and hardness properties of TiB2– Fe coating developed on AISI 1020 steel by tungsten inert gas (TIG) cladding

The present work is attempted to improve the microhardness and wear properties of AISI 1020 steel by depositing TiB₂–Fe composite coating using tungsten inert gas (TIG) cladding. In this study, different compositions of TiB₂–Fe paste form were preplaced on the substrate plates and then TIG heat input was applied to deposit hard composite coating layer. The main objective of the present work was to explore the influence of TIG input current as well as iron content on the microstructure and surface properties of deposited coatings. Microhardness, microstructural and phase characterization of the coating have been done by the Vickers microhardness tester, scanning electron microscope (SEM), Energy dispersive spectroscopy (EDS) and X-ray diffractrometer (XRD). The results showed that the microhardness of the TiB₂–Fe coating was strongly influenced by the composition of the coating materials as well as the TIG processing current. The microhardness increases with decreasing Fe contents in the coating materials with constant processing current (90 A) as well as it also increases with decreasing processing current with the fixed composition of coating materials (80TiB₂–20Fe). The maximum average microhardness found was 3082 HV_0.1 for the coating of 100TiB₂–0Fe composition ratio and 90 A processing current which was about 18 times higher than that of the substrate average microhardness value (163 HV_0.1). Average wear rate evaluated by considering weight loss of the TIG cladded samples using pin on disc tribometer by the sliding distance of 864 m and 20 N normal loads. The wear results also showed that the coating contains 100 wt% of TiB₂ (0 wt% of Fe) exhibited lower rate of wear 6.74 × 10^?8 g/Nm which is about 24 times lower as compared to AISI 1020 mild steel wear rate (166.31 × 10^?8 g/Nm).     

Braking behaviours of C/C–SiC mated with iron/copper-based PM in dry,wet and salt fog conditions

C/C–SiC composites have enormous potential as a new generation of brake materials. It is worth studying the friction and wear behaviours of these materials in special environments to ensure the safe and effective braking of trains in practical applications. In this study, the braking behaviours and wear mechanisms of C/C–SiC mating with iron/copper-based PM in dry, wet and salt fog conditions are compared in detail. The results show that the coefficient of friction (COF) in the wet condition is reduced by 14.13% compared with that under the dry condition. The COF value of the first braking under salt fog condition is increased by 12.27% and 30.75% compared to the dry and wet conditions, respectively. Additionally, the tail warping phenomenon of the braking curve disappears in wet condition, which is attributed to the weak adhesion of friction interfaces and the lubrication of the water film. The main wear mechanisms of C/C–SiC mating with iron/copper-based PM under dry condition are adhesive, fatigue and oxidation wear. However, the dominant wear in wet condition is abrasive wear. The cooling and lubrication of water reduce the tendency of thermal stress, and weaken adhesive and fatigue wear. Furthermore, salt fog can accelerate the corrosion of alloy friction film, leading to the damage of friction film. Meanwhile, the third body particles formed in salt fog condition participate in the braking process. The wear mechanisms in salt fog condition are dominated by abrasive and delamination wear.     

Microstructures and properties of nickel-titanium carbide composites fabricated by laser cladding

In this work, Ni/TiC composites were synthesized by the laser cladding technique (LCT). A scanning electron microscope (SEM), X-ray diffractometer (XRD), microhardness meter, electrochemical workstation, and friction and wear tester examined the microstructure, surface morphology, phase structure, microhardness, wear, and corrosion resistances of the Ni/TiC composites. These results indicated the Ni/40TiC composite contained finer equiaxed crystals than the Ni and Ni/20TiC composites. In addition, numerous TiC particles in the Ni/40TiC composite impeded growth of the nickel crystals, which resulted in the fine microstructure of the Ni/40TiC composite. The Ni, Ni/20TiC, and Ni/40TiC composites exhibited face-centered cubic (f c c) lattices. The average microhardness values of the Ni/20TiC and Ni/40TiC composites were approximately 748 HV and 851 HV, respectively. The Ni/40TiC composite had the lowest friction coefficient (0.43) among all three coatings, and only some shallow scratches appeared on the surface of the Ni/40TiC composite. The corrosion potential (E) of Ni/40TiC exceeded the Ni/20TiC composite, and both were larger than the Ni composite, which indicated the Ni/40TiC composite had outstanding corrosion resistance and the Ni composite had poor corrosion resistance. The corrosion current densities (i) of Ni, Ni/20TiC, and Ni/40TiC composites were 5.912, 4.405, and 3.248 μA/cm², respectively.     

Microstructure,mechanical, tribological,and oxidizing properties of AlCrSiN/AlCrVN/AlCrNbN multilayer coatings with different modulated thicknesses

Multilayer structure design is one of the most promising methods for improving the comprehensive performance of AlCrN-based hard coatings applied to cutting tools. In this study, four types of AlCrSiN/AlCrVN/AlCrNbN multilayer coatings, with different modulated thicknesses, were deposited to investigate their microstructure, mechanical, tribological, and oxidizing properties. All multilayer coatings exhibited grain growth along the crystallographic plane of (200) with a NaCl-type face-centered cubic (FCC) structure. The results show that, as the modulation thickness decreases from ～35 nm to ～10 nm, (1) the grain refinement effect is increasingly evident; (2) all multilayer coatings show a hardness of >30 GPa and an elastic modulus of >300 GPa. Both the ability to resist elastic strain to failure and the plastic deformation of multilayer coatings increase. In addition, their resistance to cracking reduces; (3) the wear rates of these multilayer coatings reduce successively from 1.78 × 10^?16 m³ N^?1 m^?1 to 7.7 × 10^?17 m³ N^?1 m^?1. This is attributed to an increase in self-lubricating VO_x and a decrease in adhesives from the counterparts; (4) the best high-temperature oxidation resistance was obtained for the multilayer coating with a modulated thickness of ～15 nm.     

Dependence of mechanical and tribological performance on the microstructure of (CrAlTiNbV)Nx high-entropy nitride coatings in aviation lubricant

The (CrAlTiNbV)N_x coatings are fabricated by controlling the substrate bias via magnetron sputtering method. Under low substrate bias, the coating tends to form a loose columnar crystal structure with (200) preferred orientation. However, when the substrate bias increases, the coating transforms into a dense nanocrystalline structure, and the (111) orientation is enhanced. As the substrate bias increases, the residual stress and hardness of the coating gradually increase, while the adhesion strength decreases slightly. Friction tests show that the coating possesses the lowest average friction coefficient (about 0.06) and wear rate (8.7 × 10^-9 mm³/N·m) in 4050# aviation lubricant, which is achieved under the substrate bias of -96 V and -126 V, respectively.     

Microstructure,wear and corrosion characteristics of multiple-reinforced (SiC–B4C–Al2O3) Al matrix composites produced by liquid metal infiltration

In this study, AA7075 aluminum matrix composites reinforced with the combination of SiC, Al₂O₃, and B₄C particles were fabricated by the liquid metal infiltration method. The effects of the relative ratio of B₄C and Al₂O₃ particles on the microstructural, wear, and corrosion features of the composite samples were analyzed using XRD, light metal microscopy, SEM, EDS, Brinell hardness, ball-on-disc type tribometer, and potentiodynamic polarization devices. It was determined that infiltration occurred more successfully, and homogenously distributed particles with reduced porosity were obtained as the amount of Al₂O₃ increased. Worn surface studies revealed that the specimens were predominantly worn by abrasion and adhesion. The increase in B₄C/Al₂O₃ ratio caused a decrease in the hardness and wear strength, whereas it increased the corrosion resistance.     

Numerical simulation analysis and experimental validation on wear/fracture mechanisms of polycrystalline cubic boron nitride superabrasives in high-speed grinding

In this study, a two-dimensional finite element model is proposed to investigate the wear/fracture mechanisms of polycrystalline cubic boron nitride (PCBN) superabrasives in high-speed grinding process. The special geometric microstructures of PCBN grains are constructed by using the classic Voronoi tessellation technique, and cohesive elements are embedded into the geometric model of PCBN grains as the potential crack propagation paths for simulating the wear/fracture behaviours of PCBN grains under grinding loads. The effects of uncut chip thickness per grain (a_gmax) on the stress distribution characteristics and wear/fracture behaviours of PCBN grains during grinding are discussed in detail. Results show that the wear behaviour of PCBN grains during grinding mainly occurs around the grain vertex region; however, the fracture behaviour, leading to the quick failure of PCBN grains, is prone to appear around the grain–filler bonding interface, which is usually on the opposite side of the in-feed direction. Moreover, to separate the PCBN grains from the macro-fracture during grinding, the uncut chip thickness per grain should be kept smaller than 1.0?µm to prevent the unfavourable fracture behaviour from appearing around the grain–filler bonding interface. Furthermore, the corresponding single-grain grinding trials are performed to validate the numerical simulation results by evaluating the wear/fracture morphologies of the PCBN superabrasives in the actual grinding operation.     

Tribological and mechanical characteristics of AA5083 alloy reinforced by hybridising heavy ceramic particles Ta2C & VC with light GNP and Al2O3 nanoparticles

In this study, AA5083 sheets were reinforced with four different hybrid nanoparticles by friction stir processing (FSP) for the development of surface nanocomposites used in advanced engineering applications. The present research focused on improving the properties and tribological behaviour of AA5083 alloy surfaces, including novel hybrid nanoparticles and the intermetallic phase formed during FSP. A tribometer tester with a constant normal load was used to examine the tribological performance of the hybrid composites. After the wear test, a surface profiler inspector was used to analyse the morphology and surface roughness of the examined materials. The Vickers micro-hardness of the base metal and the manufactured composites were measured. During FSP, a new intermetallic phase of AlV₃ was successfully formed at 300–400 °C in the hybrid nanocomposites containing VC particles. The reinforcements resulted in additional grain refining than FSP. The AA5083/Ta2C–Al₂O₃ exhibited the greatest grain refinement, a sixty-fold reduction in grain size compared to that of the base alloy. The results revealed that the hybrid nanocomposites containing VC particles demonstrated the most significant microhardness values inside the stirred zone as a result of the presence of the AlV₃ phase, which was increased by 25–30%. Moreover, the mechanical properties were significantly improved for all manufactured nanocomposites. The tensile strength was increased by 28% through the hybridisation of AA5083 using a hybrid of VC-GNPs. The dispersion of Ta₂C-GNPs and VC-GNPs in the matrix led to excellent interfacial adhesion, resulting in an enhancement in the mechanical properties. The AA5083/VC-GNPs surface composite outperformed other manufactured composites regarding wear resistance. In addition, due to GNPs soft nature, it reduced the coefficient of friction (COF) of the manufactured composites by 20–25% compared to other reinforcements.     

Improving tribocorrosion performance of chemically bonded ceramic phosphate coating reinforced by GO-ZnO

To enhance the tribocorrosion properties of chemically bonded phosphate ceramic coating (CBPCC), GO-ZnO was prepared and added into CBPCC. And the tribocorrosion behaviour of CBPCC was investigated. Results show that, with the introduction of GO-ZnO, the open circuit potential of CBPCC shifts in a positive direction and corrosion current density decreases. In addition, the total material loss, the total mechanical wear loss and the total electrochemical corrosion loss of CBPCC all decrease with the increase of GO-ZnO. The wear track of CBPCC after tribocorrosion without GO-ZnO is rough and porous, while the wear track becomes smooth and dense with the incorporation of GO-ZnO. The material in wear track is anchored by GO-ZnO due to the strong bond between GO-ZnO and CBPCC, which decreases the wear loss. Because of the extra force from the tribocorrosion experiment, the material anchored by GO-ZnO forms to a dense structure which prevents electrolyte diffusion into CBPCC. Moreover, GO-ZnO can block the electrolyte diffusion pathway and make it more tortuous. The resistance to the electrolyte diffusion decreases the corrosion current density and the increased wear loss due to electrochemical corrosion.