Thermostability,oxidation, and high-temperature tribological properties of nano-multilayered AlCrSiN/VN coatings

In this study, monolithic AlCrSiN, VN, and nano-multilayered AlCrSiN/VN coatings were deposited using a hybrid deposition system combining arc ion plating and pulsed direct current magnetron sputtering. The microstructure, thermostability, mechanical, oxidation and tribological properties of the coatings were comparably investigated. The multilayered AlCrSiN/VN coating exhibited a face-centered cubic (fcc) structure with (200) preferred orientation and showed the highest hardness (30.7 ± 0.5 GPa) among these three coatings due to the multilayer interface enhancement mechanism and higher compressive stress. The AlCrSiN sublayers effectively prevented the V element from rapid outward diffusion to the surface of AlCrSiN/VN coating at elevated temperatures, which improved the oxidation resistance of the coating. Decomposition of V (Cr)–N bonds occurred at annealing temperatures from 800 °C to 1000 °C and V₂N phase appeared at 1100 °C. The AlCrSiN/VN coating showed excellent tribological performance at high temperatures by combining the merits of VN layers for low friction coefficient and AlCrSiN layers for superior oxidation resistance. Compared to VN and AlCrSiN coatings, AlCrSiN/VN coating showed the lowest wear rate of 2.6×10^-15 m³/N·m at 600 °C and lowest friction coefficient of 0.26 at 800 °C with a relativity low wear rate of 39.4×10^-15 m³/N·m.     

Effects of nitrogen flow rate on the microstructure and mechanical and tribological properties of TiAlN films prepared via reactive magnetron sputtering

In this study, TiAlN ceramic films were fabricated via reactive magnetron sputtering on a Ti6Al4V titanium alloy substrate. The effects of N₂ flow rates on the microstructure and mechanical and tribological properties of the films were systematically studied. With increasing N₂ flow rate, the films underwent a morphological evolution from a fine columnar structure to a coarse structure with holes and microcracks. In addition, the preferred orientation of the films varied from TiAlN (220) to the (111) plane. However, a high N₂ flow rate (≥20sccm) resulted in target poisoning and reduced the deposition rate, which resulted in defects such as cavities and holes on the surface. Moreover, with increasing N₂ flow rate, the hardness and elastic modulus first increased and then reduced owing to grain refinement. The films deposited at a N₂ flow rate of 16 sccm exhibited the smallest wear width and the lowest wear rate. As the N₂ flow rate increased from 12 to 24 sccm, the wear mechanism of the films changed from abrasive and adhesion wear to abrasive wear caused by severe plastic deformation, which was directly related to the microstructural evolution and mechanical properties.     

Improving the mechanical and tribological properties of TiB2/a-C nanomultilayers by structural optimization

A novel nanomultilayered architecture was developed through magnetron sputtering to simultaneously achieve excellent mechanical and tribological properties in TiB₂/a-C film. Structural optimization was conducted by adjusting the modulation period from 1 to 10.5 nm. Film hardness and toughness were significantly improved and reached the optimal value at Λ = 6.6 nm. Combination of a sufficient number of heterointerfaces and appropriate individual layer thickness played a key role in hardening and toughening. The internal stress increased linearly with the increase in modulation period, which may be related to the reduction in the number of interfaces. Furthermore, a low friction coefficient of about 0.1 was achieved in the steady state at Λ ≤ 6.6 nm due to the formation of a uniform and compact transfer film on the worn ball surface. The improved mechanical performance and the presence of an effective transfer film resulted in an outstanding anti-wear performance at Λ = 6.6 nm.     

Positive modification on the mechanical,tribological and oxidation properties of AlCrNbSiN coatings by regulating the Nb/Si-doping ratio

The precise control of Nb/Si-doping ratio is the critical factor to tailor AlCrNbSiN coatings with superior comprehensive properties. In this study, the effect of Nb/Si-doping ratio on the microstructure, mechanical, tribological and oxidation properties of AlCrNbSiN coatings was systematically researched. With the increase of Nb/Si-doping ratio, coatings’ microstructures changed from a featureless dense structure to a columnar and equiaxed mixed microstructure gradually. The main phase was transformed from the solid solution phase of h-Al(Cr)N for Nb-free coating (Nb/Si = 0:1) to c-Al(Cr)N solid solution for three Nb-containing coatings (Nb/Si = 1:2, 1:1 and 2:1). When Nb/Si ratio is 1:1, the formation of harmful h-NbN phase was found in the coating. The performance results indicated that, (1) The AlCrNbSiN coating with the Nb/Si ratio of 2:1 achieved optimal hardness (~34.9 GPa), toughness (CPRs ~569.3) and the minimum wear rate of 2.34 × 10⁻⁶ mm³/(N·m); (2) When the Nb/Si-doping ratio is 1:2, the coating exhibited the best oxidation resistance, attributing to the sufficient (Al, Si)O_x oxidation protective layer and only a small amount of AlNbO₄ and CrNbO₄ formed at 1200 °C.     

Effects of Ti2SnC on the mechanical properties and tribological properties of copper/graphite composites

Copper/graphite composites and copper/graphite/Ti₂SnC composites were fabricated through the process of ball-milling, pressing and sintering. The effects of Ti₂SnC as the second lubrication component on the mechanical properties, wear resistance and lubrication properties of copper/graphite composites were studied in this paper. The results showed that copper/graphite/Ti₂SnC composites had better hardness, impact toughness, wear resistance and lubrication performance than copper/graphite composites. The optimum values of hardness, impact toughness, friction coefficient and wear rate of copper/graphite/Ti₂SnC composites were, respectively, 56 HSD, 1.8J/cm², 0.15, 9.126 × 10^?6 mm³/N·m, while these were only 45 HSD, 1.2 J/cm², 0.17, 3.534 × 10^?4 mm³/N·m of copper/graphite composites.     

Improved mechanical and wear properties of hybrid Al-Al2O3/GNPs electro-less coated Ni nanocomposite

Al was successfully reinforced with two ceramics Al₂O₃ coated Ni and graphene nanoplatelets (GNPs) coated Ni by electro-less deposition technique to form Al-Al₂O₃/$\mathit{x}$ GNPs hybrid nanocomposite ($\mathit{x}=0,0.2,0.6,1$and $1.4\%$) with improved mechanical and wear properties. Compressive strength, hardness, wear properties and coefficient of friction were investigated. The results indicated that increasing GNPs volume fraction improves compressive strength, hardness and antifriction properties of composites significantly. In comparison with pure aluminum, 1.52- fold increases in the strength, 2.45-fold increase in the hardness and 19.2-fold decreases in the wear rate of Al-10%Al₂O₃/1.4%GNPs nanocomposite are achieved. This improvement is attributed to the remarkable mechanical strength and excellent self-lubrication of grapheme, the reduction of grain size during electro-less deposition process and the increased efficient stress transfer due to the curled structure of GNPs. Additionally, coating GNPs with Ni particles prevent the formation of Al₃C₄ intermetallic phase which lead to this large improvement in the wear rate. In comparison with the available results in the literature, electro-less coating of GNPs with Ni provides 2.1 times larger hardness than composite with uncoated GNPs.     

Effect of Ti particle size on mechanical and tribological properties of TiCN coatings prepared by reactive plasma spraying

Titanium carbonitride (TiCN) coatings were successfully fabricated by reactive plasma spraying (RPS) from agglomerated Ti-graphite feedstock. The effect of Ti particle size on the microstructure and phase composition of plasma sprayed TiCN coatings was investigated. The Vickers microhardness of coatings was measured by a Microhardness Test and the corresponding Weibull distribution were also analyzed. In addition, a pin-on-disk tribometer was employed to determine the trobological properties of coatings. Results show that all the coatings consist of TiC_xN_1−x (0 ≤ x ≤1) and minor Ti₂O phases, and the amount of Ti₂O increases with the increase of Ti particle size. The Weibull distribution of Vickers microhardness of all the coatings shows apparent scattering, while the coating sprayed with Ti particle size of 28 µm exhibits a relatively even distribution. Compared with the coating sprayed with Ti particle size of 14 µm or 48 µm, the coating sprayed with Ti particle size of 28 µm exhibits improved mechanical and tribological properties, which are attributed to the high microhardness and strong bonding strength.     

Superior mechanical and tribological properties governed by optimized modulation ratio in WC/a-C nano-multilayers

WC/a-C nano-multilayers with different modulation ratio (WC:a-C) ranging from 1:10 to 1.5:1 were deposited by fixing a-C individual layer thickness and tailoring WC individual layer thickness. The effect of modulation ratio on mechanical and tribological performance of WC/a-C nano-multilayers were investigated. Superior mechanical and tribological properties were simultaneously achieved at modulation ratio of 1:1.2. In addition to the improvement of mechanical properties, the improved tribological properties should also be attributed to the friction-induced formation of a WO₃-rich transfer film under an appropriate WC individual layer thickness, which combing the graphitized worn film surface constructed an intrinsically weak-interacting sliding interface (WO₃/C interface). Also, graphitized carbon is an essential coadjutant for the formation of WO₃-rich transfer film.     

Microstructure evolution,mechanical and tribological properties of Ti3(Al,Sn)C2/Al2O3 composites

In this paper, in situ formed Ti₃(Al,Sn)C₂/Al₂O₃ composites were fabricated by sintering the mixture of Ti₃AlC₂ and SnO₂. The Al atoms could diffuse out of the Ti₃AlC₂ layered structure to react with SnO₂, resulting in the formation of Ti₃(Al,Sn)C₂ solid solution and Al₂O₃. When the SnO₂ content was 20?wt.%, the sintered Ti₃(Al,Sn)C₂/Al₂O₃ composite exhibited the best overall mechanical properties, because of the optimized cooperative strengthening effect of solution strengthening and Al₂O₃ enhancement. When the SnO₂ content increased up to 30?wt.%, the flexural strength and fracture toughness of Ti₃(Al,Sn)C₂/Al₂O₃ composite dramatically decreased on account of the large accumulation of generated Al₂O₃. Moreover, according to the SiC ball-on-flat wear tests, it was found that the wear resistance of Ti₃(Al,Sn)C₂/Al₂O₃ composites was significantly improved as the SnO₂ content increased.     

Microstructure,mechanical and tribological properties of TaCN composite films by reactive magnetron sputtering

In this paper, a series of TaCN composite films with different carbon content were deposited by the magnetron sputtering system and the microstructure, mechanical and tribological properties were investigated. The results showed that the deposited TaCN films exhibited a three-phase of face-centered cubic (fcc) Ta(C,N), hexagonal closed-packed (hcp) Ta(C,N) and amorphous CNx. With the increase of carbon content, the hardness of the TaCN films first increased and then decreased, after reaching a maximum of 33.1 GPa; the adhesion strength increased gradually; the coefficient of friction decreased monotonically and the wear property initially improved and then weakened at room temperature. The coefficient of friction of the TaCN film at 28.21 at.% carbon decreased first, then increased and then decreased again and its high-temperature wear rate first decreased slightly and then increased, as the temperature increased from room temperature (RT) to 600 °C. The TaCN film at 28.21 at.% carbon exhibited excellent an elevated-temperature tribological properties.     

Microstructure,mechanical and tribological properties of WC-WCoB coating

A new kind of WC-based coating with superhard WCoB compound as the binder was fabricated by the high velocity oxy-fuel spraying of WC-WB-Co powder. The microstructure, mechanical and tribological properties of the WC-WCoB coating were investigated, together with those of the conventional WC-Co coating for comparison. The results demonstrated that the WC-WCoB coating has simultaneously improved hardness and fracture toughness, and thus remarkably decreased wear rate as compared to the conventional coating. The enhanced tribological properties of the WC-WCoB coating are attributed to the low plastic deformation and the resultant inhibition of the micro-ploughing wear and the increased fracture toughness and interfacial bonding, which can reduce the amount of large cracks. Moreover, the high intrinsic hardness of WC and WCoB, as well as their good interfacial bonding, are more effective in resisting against wear as compared with the conventional coating.     

Effect of hBN addition on the fabrication,mechanical and tribological properties of Sialon materials

This work aims to investigate the effect of hBN on the friction and wear resistance of Sialon composite. Sialon and its composite with 10 wt% hBN were fabricated by SPS sintering. The effect of hBN additive on the phase composition, microstructure, densification behavior, mechanical and dry sliding tribological properties of Sialon material was studied. Being sintered at 1600 °C for 10 min, compared to monolithic Sialon, Sialon-hBN composite has more refined β-Sialon grains with smaller aspect ratios and slightly declined relative density. The hardness of the Sialon-hBN composite was reduced due to the weak bonding between Sialon and hBN grains. Nevertheless, its fracture toughness increased ascribing to the toughening mechanisms, including crack deflection and crack bridging. hBN had an essential impact on the tribological performances of the composite due to its lower friction coefficient and good lubrication action. Under the same densification level (i.e., with a relative density of around 97.5%), the friction and wear resistance of Sialon-hBN composite were much better than monolithic Sialon. The main wear mechanisms were tribolayer formation, oxidized wear, and abrasive wear.     

Microstructural,mechanical and tribological properties of suspension plasma sprayed YSZ/h-BN composite coating

Brittleness, relative high friction coefficient and wear rate limit the applications of ceramic coatings as wear-resistant layers. However, because embedding additives with ceramic matrix has demonstrated to be an effective way to improve coating performances, different contents and size of h-BN were added into an YSZ suspension. Afterwards, the YSZ/h-BN composite coatings were manufactured by suspension plasma spray and their tribological analysis indicated that: i) the reduction of the friction coefficient and wear rate can be achieved by incorporating h-BN into YSZ coating. ii) finer h-BN particle is more helpful to enhance the tribological properties of the coating. iii) the optimum content is dependent on h-BN particle sizes. iv) when the contents and the size of the h-BN inclusion increase, the probability distribution of the micro-hardness can become bi-modal. Three worn surface conditions were summarized and their wear mechanisms were discussed as well.     

Mechanical and tribological properties of TiB2-SiC and TiB2-SiC-GNPs ceramic composites

TiB₂-SiC and TiB₂-SiC-graphene nanoplatelets (GNPs) composites were prepared using field-assisted sintering technology at 2100 °C in argon atmosphere, and the influence of the SiC and different GNPs addition on microstructure development, mechanical and tribological properties has been investigated. Instrumented hardness, bending strength, chevron-notched fracture toughness and ball-on-flat tribological tests were used for the testing and characterization of the composites. The addition of SiC significantly improved the bending strength and elastic modulus with values of 601 MPa and 474 GPa, respectively, but decreased the fracture toughness with a value of 4.8 MPa.m^1/2. The addition of GNPs has a positive effect on fracture toughness and flexural strength but a negative one on the hardness. The increasing amount of both GNPs has a positive influence on wear characteristics of the composites thanks to the described wear mechanisms.     

Mechanical and tribological properties of alumina-MWCNTs composites sintered by rapid hot-pressing

Alumina – MWCNTs composites were prepared using a novel approach. This process comprises functionalization of MWCNTs and stabilization of alumina-MWCNTs dispersion with subsequent freezing, which resulted in formation of granulated powders with homogeneous distribution of MWCNTs. The granulated powders were sintered by rapid hot pressing (RHP) at 1550 °C. Relative densities, microstructural analysis, tribological properties, fracture toughness and bending strength of prepared composites were investigated to reveal the effect of MWCNTs. Compared to pure alumina, bending strength and fracture toughness of dense alumina-5 vol.% MWCNTs composites decreased about 37% and 18%, respectively. At higher MWCNT contents, strength remained almost constant and fracture toughness slightly increased. Thus, the positive effect of CNTs on fracture toughness was demonstrated despite their counteracting effect on the refinement of the microstructure.     

Correlation between micro/nano-structure,mechanical and tribological properties of copper-zirconia nanocomposites

Fine-grained copper (Cu) and copper-zirconia (Cu–ZrO₂) nanocomposites were produced by high-energy ball milling up to 20 h. Scan Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD), microhardness, wear rate and coefficient of friction measurements were performed to investigate the correlation between micro/nano-structure changes of powder and consolidated samples and the properties of the produced nanocomposites. Cu and Cu–15%ZrO₂ nanocomposites with 49.3 and 24.4 nm crystal size, respectively, were produced after 20 h milling achieving 1.76- and 3-times larger hardness than the as received Cu. The wear rate of milled Cu was slightly decreased than the as received Cu, however, it was highly reduced for Cu–15%ZrO₂ nanocomposites reaching 10-times lower than the as received Cu. SEM, TEM and XRD analysis revealed that four main strengthening mechanisms lead to the great improvement of Cu–ZrO₂ nanocomposites properties. The major strength improvement occurred due to Orowan and dislocation strengthening mechanisms activated by the well dispersion of ZrO₂ nanoparticles in Cu matrix and their impedance to dislocation movement, respectively. Besides these two main strengthening mechanisms, work hardening and grain refinement acted as minor strengthening mechanisms for Cu–ZrO₂ nanocomposites while they are the main strengthening mechanisms of Cu samples.     

Influence of Cu on the mechanical and tribological properties of Ti3SiC2

Ti₃SiC₂/Cu composites with different contents of Cu were fabricated by mechanical alloying and spark plasma sintering method. The phase composition and structure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The mechanical and tribological properties of Ti₃SiC₂/Cu composites were tested and analyzed compared with monolithic Ti₃SiC₂ in details. The results show that the Cu leads to the decomposition of Ti₃SiC₂ to produce TiC_x, Ti₅Si₃C_y, Cu₃Si, and TiSi₂C_z. The friction coefficient and wear rate of the composites are lower than that of monolithic Ti₃SiC₂, which is ascribed to the fixing effect of hard TiC_x, Ti₅Si₃C_y, and Cu₃Si to inhibit the abrasive friction and wear. However, at elevated temperatures (ranging from room temperature to 600 °C) the friction and wear of the composites are higher than those at room temperature. Plastic flowing and tribo-oxidation wear accompanied by material transference contribute to the increased friction and wear at elevated temperatures.     

Effects of Ni content on microstructure,mechanical properties and Inconel 718 cutting performance of AlTiN-Ni nanocomposite coatings

AlTiN-Ni coatings with various Ni contents (0–3?at%) were deposited using cathodic arc evaporation. X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, a nanohardness tester, scratch-adhesion tester, and cutting tester were used to examine the microstructure, mechanical properties, and cutting performance of the coatings. The AlTiN coatings exhibited a columnar structure, while the AlTiN-Ni coatings exhibited a nanocrystal structure due to the formation of nc-AlTiN/Ni nanocomposite coatings. The nanohardness of the AlTiN-Ni coatings decreased from 26.2?GPa to 20.9?GPa as the Ni content increased from 0 to 3?at%. At an Ni content of 1.5?at%, the coating possessed a high toughness and sufficient adhesion strength; however, these dropped drastically for the AlTiN-Ni coating with 3?at% Ni owing to the presence of amorphous Ni. The results for the Inconel 718 turning indicated that the wear mode is adhesion at the rake face, abrasion and adhesion (built-up edge) at the flank face, and chipping at the cutting edge. Compared to AlTiN-Ni₃ and AlTiN-coated tools, the lifetime of the AlTiN-Ni_1.5 coated tool increased to 160% at a cutting speed of 40?m/min. This was attributed to less adhesion at the rake face and chipping at the cutting edge, due to the nanocrystal structure and higher toughness of the AlTiN-Ni_1.5 coating.     

The tribological performance of TiN,WC/C and DLC coatings measured by the four-ball test

An innovative approach to improving the wear resistance and load-carrying capacity of surfaces is by development of novel systems featuring coating treatment. Evaluation of the tribological performance of three physical vapor deposition (PVD) coatings, namely, TiN, WC/C, and DLC (diamond-like carbon), is necessary to determine their suitability as coatings for high-speed and heavy-duty power-transmitting gears. The uncoated and coated steel balls were subjected to four-ball tests under lubricated conditions. An optical microscope and a scanning electron microscope were used to observe wear scars, and energy-dispersive X-ray analysis was performed to determine the chemical compositions of the materials; these methods were also used to analyze the wear mechanisms. The wear performance of the three coatings was compared, and a four-ball method extreme pressure test was performed to determine the last nonseizure load of each tribo-pair. The WC/C and DLC coatings showed excellent tribological performance under high contact pressures and thermal loads, and the benefits of these coatings increased with decreasing performance of the lubricating medium. Therefore, WC/C and DLC coatings are suitable for application in high-speed and heavy-duty gears. Oxidation wear and peeling, fatigue pitting, and adhesive transfer are the main coating failure modes of the TiN, WC/C, and DLC coatings, respectively.     

Synergistic optimization of mechanical and tribological properties of TiC modified copper-graphite composites by direct current in-situ sintering

The application of Cu-graphite composites in the field of friction materials is limited by the poor wettability between Cu and graphite and weakened mechanical properties. In this work, in-situ TiC layers were generated by interfacial resistance sintering with direct current to manipulate the interfacial bonding of the composites and enhance their comprehensive properties. The Ti added to the composites would react with graphite at the interface to generate TiC layers and form strong Cu–TiC-graphite interfaces due to interfacial reactions. When the added Ti content is 6 wt%, the composite demonstrates the most excellent mechanical properties and tribological characteristics, i.e., yield strength (168 MPa) and wear rate (2.7 × 10⁻¹⁰ m²/N) are 93.1% higher and 29.7% lower than those of the Cu-graphite composite without Ti addition, respectively. The dense TiC layer induces the strengthening of the Cu matrix and serves as the reinforcing phase to optimize the interfacial bonding and stress transfer, which not only greatly enhances the mechanical properties of the composite but also enables the composite to take full advantage of the hard TiC and graphite phases to obtain stable friction coefficient and low wear rate. This work provides a simpler technique to prepare modified Cu-graphite composites with excellent performance and contributes to the in-depth understanding of the enhancement mechanism of hard ceramic layers on the mechanical and tribological properties of composites.