Tribochemistry of TiN films sliding against ceramic counterparts in vacuum condition and N2 atmosphere

With the rapid development of aerospace technology, the tribological performance of moving parts under extreme operating conditions has attracted a great deal of attention and interest. The application of solid lubricant coatings has become a major means of improved performance to ensure stable operation. Although molybdenum disulfide (MoS₂) and diamond-like carbon (DLC) films have excellent low coefficients of friction, they are prone to failure in vacuum because they cannot overcome the challenges of assembly in atmospheric environments. Surprisingly, unexpected results were obtained in this study using conventional nitride films. Specifically, the friction coefficient of TiN/SiC friction pair in vacuum is 0.21 and the wear rate is 8.8 × 10^?7 mm³/mN. The relatively stable friction coefficient is mainly attributed to the formation of carbonaceous lubricating layer at the interface, which is the decisive factor in reducing wear. The friction coefficient of TiN/WC friction pair under N₂ atmosphere is 0.31 and the wear rate is 4.5 × 10^?7 mm³/mN. It can be summarized as follows: first, the mechanochemical induced chemical reaction of the interface, and secondly, the thermally excited nitrogen atoms saturate the dangling bonds of the transfer film. The results further reveal the friction mechanism of TiN films with advanced ceramic materials under harsh conditions and suggest a guide for engineering applications.     

Tribological behavior studies of chemically bonded phosphate ceramic coatings reinforced with modified multi-walled carbon nanotubes (MWCNTs)

To improve the wear resistance of the chemically bonded phosphate ceramic coatings, MWCNTs are selected as the reinforcement after the modification. The high temperature wear experiment is carried out to investigate the wear behavior of the coatings with different temperatures. The results suggest that, when the temperature is below 500℃, MWCNTs can decrease friction coefficient, and the lowest friction coefficient is about 0.28, but MWCNTs lose the lubricant function at 500℃ and the friction coefficient keeps at the level of ~ 0.68. In addition, the wear resistance of coatings is improved with the introduction of MWCNTs at 100℃ and 300℃ (the wear rate is below 15X10^-3mm³/Nm), but keeps similar level at 500℃ (the wear rate is ~ 22 × 10⁻³mm³/Nm). Besides, the wear mechanism of the coatings reinforced by MWCNTs is also investigated based on the wear behavior and microstructural characterizations. MWCNTs improve the fracture toughness by preventing the crack generation and forming the bridge when crack occurs, which leads to smooth wear tracks and good wear resistance of coatings. The coatings with MWCNTs achieve poor wear resistance at 500℃ because MWCNTs lose their strength and resistance to fatigue by oxidizing.     

粘结剂对超音速火焰喷涂碳化钨涂层磨粒磨损性能的影响

采用超音速火焰喷涂(HVOF)工艺在35钢基体上制备了WC-10Ni涂层和WC-12Co涂层,研究了镍、钴这两种粘结剂对WC涂层的显微硬度、摩擦系数和抗磨粒磨损性能的影响,采用扫描电子显微镜观察涂层磨损前后的表面形貌,探讨了WC涂层的磨粒磨损机理。结果表明,以HVOF方法制备的2种WC涂层均有较高的显微硬度,WC-10Ni涂层和WC-12Co涂层与SiC砂纸摩擦副之间的干摩擦系数相差不大。2种涂层在低载荷下均有较好的抗磨粒磨损性能,但在较高载荷下WC-12Co涂层的抗磨性明显优于WC-10Ni涂层。2种涂层的磨粒磨损形式主要为均匀磨耗磨损,磨损机理以微切削和微剥落为主。WC-12Co涂层的磨损表面损伤较轻微,综合性能优于WC-10Ni涂层。     

Advanced TiC/a-C:H nanocomposite coatings deposited by magnetron sputtering

TiC/a-C:H nanocomposite coatings have been deposited by magnetron sputtering. They consist of 2–5 nm TiC nanocrystallites embedded in the amorphous hydrocarbon (a-C:H) matrix. A transition from a columnar to a glassy microstructure has been observed in the nanocomposite coatings with increasing substrate bias or carbon content. Micro-cracks induced by nanoindentation or wear tests readily propagate through the column boundaries whereas the coatings without a columnar microstructure exhibit substantial toughness. The nanocomposite coatings exhibit hardness of 5–20 GPa, superior wear resistance and strong self-lubrication effects with a friction coefficient of 0.05 in air and 0.01 in nitrogen, under dry sliding against uncoated bearing steel balls. Especially, reversible transitions from low to ultra-low friction are observed if the atmosphere is cycled between ambient air and nitrogen. The lowest wear rate is obtained at high humidity.     

Self-lubrication and wear-resistance mechanism of graphene-modified coatings

To reduce the friction coefficient of WC-17Co wear-resistant coatings, Graphene oxide were used to mix with WC-17Co powder. The SEM, EDS and Raman results were used to analyze the morphology and phase composition of graphene oxide in the powder and coating obtained by plasma spraying processes. The mechanical properties of the coatings were studied by using a microhardness tester and a universal testing machine. The friction and wear properties of the coatings were studied by using a UMT-2 friction and wear tester. The results show that among the pulverization processes, the spray granulation process can achieve a stronger and more uniform adhesion of graphene oxide on the surface of WC-17Co particles, and the graphene oxide content in the coating is higher. Graphene is still embedded in the coating as transparent, thin sheets. The bonding strength is approximately 63 MPa, the hardness is approximately 931 HV0.1, and the friction coefficient of the graphene oxide coating is reduced by approximately 22% compared to that of the coating without graphene. The formation of lubrication films in the micro-area improves the self-lubrication and antiwear effects.     

相结构对Ni-Co合金镀层摩擦磨损性能的影响

采用硫酸盐体系电镀Ni-Co合金镀层,考察了钴含量对合金镀层相结构的影响,并进一步研究了相结构对镀层摩擦磨损性能的影响.实验发现:随着镀层中钴含量的增加,合金镀层由面心立方结构逐渐向密排立方结构转变.干摩擦条件下,面心立方结构的Ni-Co合金镀层具有较高的摩擦系数和较差的耐磨性.相比之下,密配六方结构的合金镀层起到了很好的减摩和抗磨作用,其摩擦系数降低了2/3,磨损率降低1个数量级以上.     

Friction behavior of TiN–MoS2/PTFE composite coatings in dry sliding against SiC

To improve the dry friction behavior of traditional hard coatings, MoS₂/PTFE lubricating coatings were prepared on the PVD TiN-coated cemented carbide using spray method. The influences of MoS₂/PTFE lubricating coatings on the primary characteristics of TiN coatings were investigated. Reciprocating sliding tests were carried out with the TiN–MoS₂/PTFE coated specimen (T-M-P) under dry sliding conditions, and the tribological behaviors were compared to those of the TiN-coated one (T-N). The test results indicated that the adhesion force of coatings with substrate for T-M-P specimen increased, the surface micro-hardness, roughness and friction coefficient significantly decreased. Meanwhile, the surface adhesions and abrasion grooves of T-M-P specimen were reduced, and the main wear forms of T-M-P were abrasion wear and coating delamination. The MoS₂/PTFE lubricating coatings can be considered effective to improve the friction properties of traditional hard coatings.     

Microstructure and wear resistance of in-situ synthesized Ti(C,N) ceramic reinforced Fe-based coating by laser cladding

In order to enhance the wear resistance of Fe-based cladding layer, TiN, Ti and graphite were added into Fe313 powder and in-situ formation of Ti(C, N) ceramic reinforcement phase was carried out by laser cladding. Firstly, thermodynamic calculations were used to determine the feasibility and favorability of a chemical reaction. Then, the reaction mechanism was investigated by adding five groups of different contents and carrying out EDS and phase analysis. We report that large TiN particles do not completely decompose and in-situ synthesized TiC phase forms around large TiN particles. However, small TiN particles are completely decomposed and directly formed the Ti(C, N) phase. Finally, through the friction and wear tests, it has been observed that the friction coefficient of a sample, with three powders added, was 0.559 times smaller than the substrate and 0.725 times smaller than the initial powder, and the wear volume of the same sample was 0.365 times smaller than the substrate and 0.799 times smaller than the initial powder. Therefore, it can be concluded that the in-situ synthesis of Ti(C, N) ceramic reinforced Fe-based coatings by laser cladding greatly improves the wear resistance of the Fe313 layer.     

载荷、速度及环境温度对聚醚砜酮摩擦磨损性能的影响

利用MM—2000型和THT07—135型摩擦磨损试验机系统考察了载荷、滑动速度和环境温度对含二氮杂萘联苯型聚醚砜酮(PPESUK)摩擦磨损性能的影响，并利用扫描电子显微镜(SEM)观察分析了其磨损表面形貌及磨损机理。研究表明，干摩擦条件下，随载荷增加PPESUK的摩擦系数降低、磨损率增加；在高的滑动速度下，摩擦系数和磨损率都降低；环境温度对PPESUK的摩擦系数影响不大，并且粘着磨损是其主要磨损机理。     

聚四氟乙烯/纳米氮化钛复合材料的摩擦磨损性能研究

利用摩擦磨损试验机考察了填料含量及载荷对纳米氮化钛(TiN)填充聚四氟乙烯(PTFE)复合材料摩擦磨损性能的影响,采用扫描电子显微镜观察分析磨损表面形貌,探讨了磨损机理。结果表明,纳米TiN可以提高PTFE的硬度和耐磨性,当纳米TiN质量分数为7%时,PTFE纳米TiN复合材料的磨损量最小;随载荷的增大,PTFE/TiN复合材料的磨损量增加。PTFE纳米TiN复合材料的摩擦因数比纯PTFE小。     

Tribomechanical and microstructural properties of cathodic arc-deposited ternary nitride coatings

Sintered carbides are promising materials for surfaces that are exposed to extreme wear. Owing to their high service load, ceramic-based thin films are coated on carbides using different techniques. In this study, non-toxic and cobalt-free powder metallurgy-sintered carbide samples were coated with TiN, TiAlN, CrAlN, and TiSiN ceramic-based thin film coatings by cathodic arc physical vapor deposition. The microstructure (phase formation, coating thickness, surface roughness, and topography), mechanical properties (hardness, modulus of elasticity, and plasticity indices), and tribological properties (nanoscratch and wear behavior) of the thin film coatings were investigated. No cracks or defects were detected in these layers. The ceramic-based ternary nitride thin film coatings exhibited better mechanical performance than the TiN coating. The TiN thin film coating had the highest average surface roughness, which deteriorated its tribological performance. The ternary nitride thin film coatings exhibited high toughness, while the TiN thin film coating exhibited brittle behavior under applied loads when subjected to nanoscratch tests. The wear resistance of the ternary nitride coatings increased by nearly 9–17 times as compared to that of the TiN coating and substrate. Among all the samples investigated, the substrate showed the highest coefficient of friction (COF), while the TiSiN coating exhibited the lowest COF. The TiSiN thin film coating showed improved mechanical and tribological properties as compared to other binary and ternary nitride thin film coatings.     

Substrate effect on wear resistant transition metal nitride hard coatings: Microstructure and tribo-mechanical properties

Four types of different hard transition metal nitrides (TMN:ZrN, CrN, WN and TiN) coatings were deposited on Si (100) and 316LN stainless steel substrates using DC magnetron sputtering. A comprehensive study of microstructure and substrate dependent tribo-mechanical properties of TMN coatings was carried out. Higher hardness (H) and elastic modulus (E) were obtained for WN (H=40 GPa and E=440 GPa) and TiN (H=30 GPa and E=399 GPa) coatings. This is related to the formation of (100) and (111) preferred orientations in WN and TiN coatings, respectively. However, the less hardness and elastic modulus were obtained for ZrN and CrN coatings where (200) orientation is preferred. Remarkably, low friction coefficient (0.06–0.57) and higher wear resistance in the coatings deposited on steel substrates are directly associated with the higher resistance to plastic deformation (H³/E²) and the presence of intrinsic compressive stress. Three body wear modes enhanced the friction coefficient (0.15–0.62) and the wear rate in the coatings deposited on Si substrates. This is primarily associated with low fracture toughness of brittle single crystalline Si (100) substrates. Steel-on-steel contact was dominated in ZrN/steel sliding system. This occurs due to the severe adhesive wear mode of steel ball, whereas, the abrasive wear modes were attained for the CrN, WN and TiN coatings sliding against steel balls.     

环氧树脂基复合涂层摩擦磨损性能研究

研究了不同质量分数石墨、碳纤维、纳米ZrO2对环氧树脂(EP)涂层摩擦磨损性能的影响,并用扫描电子显微镜观察了涂层磨损表面形貌并探讨了磨损机理。结果表明:石墨质量分数为20%时复合涂层的磨损率仅为纯EP的7.75%;纳米ZrO2质量分数为4%时复合涂层的磨损率为纯EP的30%;纳米ZrO2与碳纤维以及石墨的协同作用提高了EP的摩擦磨损性能。EP复合涂层的磨损机理以粘着磨损、磨粒磨损以及疲劳磨损为主。     

纳米颗粒增强摩擦材料摩擦学性能研究

以丁腈橡胶改性酚醛树脂为基体,芳纶纤维、玻璃纤维为增强纤维,选用不同类型的纳米颗粒作为填料设计摩擦材料组分配比,并通过热压烧结制备摩擦材料。通过摩擦磨损试验机测试其在干摩擦条件下的摩擦学性能,并用扫描电镜(SEM)对材料的磨损形貌进行观察分析,以研究不同类型的纳米颗粒对摩擦材料性能的影响。研究表明:在干摩擦条件下,经过纳米颗粒改性的摩擦材料摩擦系数、硬度比未改性的材料有不同程度的提高,同时磨损率有很大程度的降低;纳米颗粒改性的摩擦材料摩擦系数、磨损率变化趋势具有一致性,均随着实验载荷、滑动速度的增大而逐渐减小;纳米颗粒改性后的摩擦材料磨损机理表现为疲劳磨损与磨粒磨损并存,而未改性的材料磨损机理主要表现为疲劳磨损。     

Characterization of TiCN and TiCN/ZrN coatings for cutting tool application

Coating a cutting tool improves wear resistance and prolongs tool life. Coating performance strongly depends on the mechanical and chemical properties of the coating material. In a machining process, the type of selected coating depends on the cutting condition because of the properties of the applied coating material. In addition, many factors, such as coating thickness, composition ratio, sequences of layers in multilayer coatings, and the deposition method influence the performance of a coating. In this study, the mechanical properties of TiCN and TiCN/ZrN were investigated using a ball on disk test. The substrate material made from a carbide-based cutting tool was also developed in-house. The analysis performed shows that the performances of TiCN and TiCN/ZrN coatings were found to be comparable to that of the commercial TiN-coated carbide-based cutting tool. Both the in-house and commercial coated inserts had significantly lower coefficient of friction than uncoated inserts, and the friction coefficient of TiCN coatings was constantly slightly lower than that of TiN coatings. Moreover, the coefficient of friction of the in-house developed TiCN was slightly lower than that of commercial TiN coating. However, the coefficient of friction of the in-house developed uncoated carbide inserts was slightly higher than that of commercial uncoated carbide inserts.     

Wear behaviors of TiN/TiCN/DLC composite coatings in different environments

Diamond like carbon (DLC) coatings have high wear resistance and low coefficient of friction and its features are being tried to be further developed. We deposited TiN/TiCN/DLC composite coatings on inconel substrates with closed field unbalanced magnetron sputtering system to improve the features of the conventional DLC coatings. Structural, chemical and bond types of the coating were obtained with the XRD, SEM, EDS and XPS analyses. Wear behaviors of the coatings were determined in atmosphere, distillated water and commercial oil conditions under low (2 N) and high (10 N) constant load values with using pin-on-disc tribo-test system. The wear results demonstrated that using the TiN/TiCN layers with the DLC coatings increased the load carrying capacity, decreased the CoF, and wear rates at the high load values.     

Tribological properties of polyimide coatings filled with PTFE and surface‐modified nano‐Si3N4

Polyimide (PI) coatings filled with PTFE and nano‐Si₃N₄ were prepared by a spraying technique and successive curing. Nano‐Si₃N₄ particles were modified by grafting 3‐aminopropyltriethoxysilane to improve their dispersion in the as‐prepared coatings. Friction and wear performances and wear mechanisms of the coatings were evaluated. The results show that the incorporations of PTFE and modified nano‐Si₃N₄ particles greatly improve the friction reduction and wear resistance of PI coating. The friction and wear performance of the composite coating is significantly affected by the filler mass fraction and sliding conditions. PI coating incorporated with 20 wt % PTFE and 5 wt % modified nano‐Si₃N₄ displays the best tribological properties. Its wear rate is more than one order of magnitude lower and its friction coefficient is over two times smaller than that of the unfilled PI coating. Differences in the friction and wear behaviors of the hybrid coatings as a function of filler or sliding condition are attributed to the filler dispersion, the characteristic of transfer film formed on the counterpart ball and the wear mechanism of the coating under different sliding conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40410.     

Influence of WS2 content on high temperature wear performance of magnetron sputtered TiN-WSx thin films

TiN-WS_x thin films with varying WS_x content were co-deposited by reactive magnetron sputtering. GAXRD analyses showed that the addition of 4 at.% WS_x led to loss of crystallinity of TiN phase and a complete amorphous characteristic was manifested upon incorporation of 19 at.% WS_x. Nanohardness results indicated that TiN-WS_x containing 4 and 19 at.% WS_x presented 19.7 GPa and 18.4 GPa, respectively, following the rule of mixtures. Friction coefficient and wear rates measured in reciprocated tribological tests revealed that TiN-WS_x coatings present an improved tribological performance when compared to pure TiN thin film at room temperature, registering friction coefficient of 0.42 ± 0.05 and 0.19 ± 0.03 for samples with 4 and 19 at.% WS_x, respectively. Wear tests at high temperatures evidenced that sample with 4 at.% WS_x did not provide advanced protection to substrate at 343 K and above due to deterioration. On the other hand, coating with 19 at.% WS_x maintained low friction coefficient up to 343 K, registering an optimum wear rate of 0.86 × 10⁻¹⁷ m²/N with no cracking occurrence.     

Microstructure,mechanical and high temperature tribological behaviour of graphene nanoplatelets reinforced plasma sprayed titanium nitride coating

In the present study, graphene nanoplatelets (GNPs: 1–2 wt. %) reinforced TiN coating were successfully fabricated over titanium alloy using a reactive shroud plasma spraying technique. All coatings were completely oxide free, while the addition of GNPs suppressed the non-stoichiometric TiN_0.3 phase. Improvement of 19%, 18% and 300% in hardness, elastic modulus and fracture toughness was achieved by mere addition of 2 wt. % GNP. The addition of GNP in TiN also reduced the wear volume loss and the wear rate of the coatings for the entire range of temperature (293–873 K). Moreover, GNPs also manifested the coefficient of friction (COF) of the coating. Post wear characterization revealed that the presence of GNP throughout the wear track even at 873 K. The multi-layer structure of GNPs assisted in long term lubricity to the surface and increased the wear resistance of the coating.     

酚醛改性环氧树脂耐磨防腐涂料的研制

利用酚醛改性环氧树脂为基料,同时添加固体自润滑材料、硬质抗磨材料、助剂等研制出一种耐磨防腐涂料。该涂料除具有良好的防腐蚀性,还具有优异的耐磨性、自润滑性及水润滑性,是抽油管杆等恶劣腐蚀条件下较理想的耐磨防腐涂料。