Nanohardness and tribological properties of nc-TiB2 coatings

The work is devoted to the investigation of nanohardness and tribological properties in TiB₂ coatings deposited on austenitic steel substrates using an unbalanced magnetron sputtering with the focus on the coatings prepared under small negative bias to reduce compressive stresses. The coating prepared under floating potential exhibited nanocomposite microstructure with the size of TiB₂ (hcp) nanocrystallites in the range of 2–7 nm. It is in contrast with the textured microstructure typically developed under higher negative bias. The reduction of the compressive stresses up to ?0.4 GPa while keeping the nanohardness >30 GPa and the coefficient of friction of 0.77 were obtained in this coating. The highest nanohardness of 48.6 ± 3.1 GPa and indentation modulus of 562 ± 18 GPa were achieved at ?100 V bias in the textured coating. The friction mechanisms include mechano-chemical formation of a tribological oxide film between the sliding partners combined with an abrasive wear.     

Effect of annealing on the cohesion,adhesion, and tribological behavior of amorphous silicon-containing diamond-like carbon (Si-DLC) coatings on steel

Amorphous silicon-containing diamond-like carbon (Si-DLC) coatings were deposited by Ar+ ion beam-assisted physical vapor deposition of tetraphenyl-tetramethyl-trisiloxane (704 Dow Corning diffusion pump oil) on AISI 4340 low alloy and 440° C high alloy steel specimens, as well as on thin wafers of the same compositions, in order to evaluate residual stresses within the coatings. During annealing in an argon atmosphere at 200°C for up to 30 min, the residual compressive stress, attributed to hydrogen entrapment during deposition, gradually changed to tensile due to loss of hydrogen, and the rate of stress increase decreased with increasing annealing time. The cohesion and adhesion failure loads of the coatings decreased with annealing time, as did the friction coefficient between the coating and a diamond stylus. The specific wear rate, measured by pin-on-disk tribometry, increased with annealing time. These properties are affected not only by the change in residual stress state during annealing, but most likely also by devitrification and the accompanying grain growth. If these effects are neglected, then the properties may be correlated directly with residual stresses in the coating.     

Nanostructure,mechanical and tribological properties of reactive magnetron sputtered TiCx coatings

This study describes the correlation between microstructure, mechanical and tribological properties of TiC_x coatings (with x being in the range of 0–1.4), deposited by reactive magnetron sputtering from a Ti target in Ar/C₂H₂ mixtures at ~ 200 °C. The mechanical and tribological properties were found to strongly depend on the chemical composition and the microstructure present. Very dense structures and high hardness, combined with low wear rates and friction coefficients, were observed for coatings with chemical composition close to TiC. X-ray diffraction and X-ray photoelectron spectroscopy analysis, used to evaluate coating microstructure, composition and relative phase fraction, showed that low carbon contents in the coatings lead to sub-stoichiometric nanocrystalline TiC_x coatings being deposited, whilst higher carbon contents gave rise to dual phase nanocomposite coatings consisting of stoichiometric TiC nanocrystallites and free amorphous carbon. Optimum performance was observed for nanocomposite TiC_1.1 coatings, comprised of nanocrystalline nc-TiC (with an average grain size of ~ 15 nm) separated by 2–3 monolayers of an amorphous a-DLC matrix phase.     

Influence of substrate treatment on the tribological properties of DLC coatings

Due to the very thin nature of DLC coatings, the substrate must carry the main part of the applied load. If the substrate has insufficient strength to carry the contact load and thus support the coating, plastic deformation will occur, leading to premature failure of the coating. The challenge to improve the properties of hard DLC coatings by thermo-chemical pre-treatment of the substrate has gained much attention in recent years, leading to a new method called duplex treatment. In the present study, a hydrogen-free hard carbon coating deposited on plasma nitrided AISI 4140 steel was investigated with respect to microhardness, residual stress, scratch adhesion and dry sliding wear resistance. The pin-on-disc results showed that nitriding of the substrate improves the wear resistance of the hydrogen-free hard carbon coating as compared to the hardened substrate. The improvement can be related to the increased load carrying capacity of the steel substrate and to improved coating to substrate adhesion.     

耐高温PAI/EP涂层的制备及摩擦学性能研究

通过溶剂法对环氧树脂(EP)和聚酰胺酰亚胺(PAI)进行共混,加入增韧剂、润滑剂、固化剂及其他助剂,制备出性能优异的耐高温耐磨涂层材料。采用热失重分析仪(TGA)、环块型摩擦磨损试验机(MRH-3G)测试了复合涂层材料的耐高温性能、摩擦磨损性能。结果表明,当PAI含量为10%时,涂层材料的降解温度可达到273℃;润滑剂总量为25%,石墨与二硫化钼(MoS_2)配比为3∶2时,其摩擦磨损性能最佳。采用扫描电子显微镜(SEM)表征了涂层磨损表面的微观形貌。结果表明,润滑剂添加过少,复合涂层表面磨损严重,出现犁沟且变形;添加过多会产生轻微裂纹,润滑膜翘起甚至脱落。采用能谱(EDS)分析了涂层表面磨损前后的元素成分,结果表明润滑剂均匀分散在基体树脂中,形成自润滑膜。     

固液研磨法制备的SBA-15介孔分子筛催化剂在纤维素氢解制低碳多元醇的研究

纤维素的催化氢解制备低碳多元醇是一种行之有效的生物质利用途径,其核心是催化剂的研究。以SBA-15为模板,引入生物碳源(大豆油),通过固液研磨法制备自还原型金属双功能催化剂x%Ni-y%W/SBA-15,并将其应用于纤维素氢解制备低碳多元醇。当镍、钨含量分别为10%和20%时,低碳多元醇的总收率最高,为51.37%。改变加氢组分,与20%W/SBA-15制成混合型双功能催化剂M+20%W/SBA-15(M=Pd/C,Raney Ni,Rh/C,Pt/C,Ir/C)催化纤维素氢解时,加入Pt/C和Ru/C的混合型催化剂催化效果最好,低碳多元醇的总收率分别为68.39%和53.43%。最后,对用固液研磨法制备自还原型金属双功能催化剂进行优缺点分析,在此基础上,对今后此法制备的催化剂在纤维素氢解中的应用进行了展望。     

Optimized a-C coatings by doping with zirconium for tribological properties and machining performance

In this study, a-C:Zr_x% coatings with various levels of zirconium (Zr) addition are deposited on cemented tungsten carbide (WC-Co) substrates using a medium frequency twin magnetron sputtering and unbalanced magnetron sputtering system. The tribological properties of the coatings are investigated by conducting wear tests against an AISI 1045 steel counterbody under a cylinder-on-disk line contact wear mode using an oscillating friction and wear tester system. The machining performance of coated turning cutters and micro-drills is then evaluated by performing turning tests and high-speed through-hole drilling tests using AISI 1045 steel counterbodies and printed circuit board workpieces, respectively. The experimental results reveal that the fabricated a-C:Zr_x% coatings not only have improved tribological properties, but also yield an enhanced machining performance. For sliding against the AISI 1045 steel counterbody under loads of 10 N and 100 N, respectively, the optimal tribological properties are provided by the a-C:Zr_13%coating. However, the optimal turning and drilling performance is obtained using the a-C: Zr_45% coating.     

Microstructure,adhesion, and tribological properties of conventional plasma-sprayed coatings on steel substrate

A variety of metallic and oxide coatings were deposited under various conditions on 1020 mild steel substrate by conventional plasma spraying. The coating thickness, microhardness, cohesion and adhesion failure loads, friction coefficient, and abrasive wear resistance were evaluated. The coatings were classified as follows, in order of decreasing microhardness and wear resistance: alumina, chromia, 316 stainless steel, Ni-5% Al, elemental aluminum and aluminum-polyester. Wear resistance increased with increasing microhardness and decreasing friction coefficient. The microhardness and wear resistance of high-velocity oxy-fuel (HVOF) diamond jet (DJ)-sprayed aluminum were found to be superior to those of plasma-sprayed aluminum. Plasma or flame-sprayed metallic coatings adhered well to the substrate. The cohesion, adhesion, microhardness, and wear resistance of alumina coatings exceeded those of equally thick chromia coatings.     

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.     

Hydrogen content influence on tribological properties of nc-WC/a-C:H coatings

Hydrogen content has high influence on low-friction properties of an amorphous carbon coating a-C with or without transition metal additions. In the paper the nanocrystalline nc-WC/a-C:H coatings deposited by means of magnetron sputtering were investigated. Hydrogen content up to 37% was obtained by the use of different flows of pure hydrogen or methane mixed with pure argon. The coatings were investigated by means of SEM, EDS, and SAED HR TEM in order to obtain thickness, sufrace morphology, chemical composition as well as nanostructure. Moreover, these were investigated: type of bonds between carbon atoms by means of Raman Shift Spectroscopy and hydrogen content by means of SIMS and inert gas fusion crucible method. Tribological properties were elaborated by means of ‘pin-on-disc’ method. It was stated that coefficient of friction, microstructure and type of bonds between carbon atoms are highly dependent from the hydrogen content. It is the main parameter for achieving of low friction coefficient (below 0.1) as well as very low wear rate (in a range of 10⁻¹⁷ m³·N⁻¹·m⁻¹. Obtained results confirmed that proposed nc-WC/a-C:H coatings can be used for improving tribological properties of hard steels and hardened titanium alloys.     

Analysis of instrumented scratch hardness and fracture toughness properties of laser surface alloyed tribological coatings

The mechanical characteristics of ceramic matrix composite (CMC) coatings are widely different from the same materials in bulk form or the individual constituents and are very important to be assessed to carry out application oriented studies on CMC coatings with novel compositions. In the present work, a composite coating of TiB₂, TiN and SiC is fabricated in-situ through a combination of high temperature chemical reaction and laser surface alloying. The formation of the surface layer is due to the laser-assisted chemical reaction followed by laser melting. A mixture of TiO₂, SiO₂, hBN and graphite in stoichiometric proportions is used as the precursor for the chemical reaction. The presence of all the reaction products in the CMC coatings developed is confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). A thorough evaluation of various mechanical properties achieved more insight into the CMC coatings developed. Hardness and fracture toughness of the coatings are measured with a scratch tester. The property evaluations are performed in a similar way for two more coatings fabricated with precursor mixtures containing more than a stoichiometric amount of SiC and hBN respectively. For comparison, a number of composites fabricated through various other routes are characterized afresh with the same set of techniques. Coatings formed with SiC in precursor show higher values of scratch hardness (14.37 GPa), microhardness (24.37 GPa) and fracture toughness (6.63 MPa-m^1/2).     

Methods for studying the mechanical and tribological properties of hard and soft coatings with a nano-indenter

This study illustrates the capabilities of a nanoindentation/nanoscratch tester to assess mechanical and tribological properties of coating films. Properties such as hardness, elastic modulus, mar and scratch resistance, and critical force for cracking can be accurately measured. Operation of the Nano-Indenter is described in detail. A scanning probe microscope (SPM) is shown to be a valuable supplement to the Nano-Indenter. Well-characterized thermoset acrylic clearcoats and thermoplastic latex films were studied. For the first time, operating parameters are described for measurement of relatively soft coatings, such as films cast from a latex with a glass transition temperature (T_g) of 8°C. Thus, the method is made available for study of most types of coatings. The method can easily discriminate between coatings with different T_gs and crosslink densities. Once operating parameters are established, it takes about 10 minutes for an indentation test and 10 minutes for a scratch test with the Nano-Indenter, and with further automation this time could be reduced. Each indentation test accurately measures hardness and elastic modulus as a function of depth within the coating, and each scratch test provides additional insight into the material’s behavior. The method is sensitive to small changes in polymer composition and formulation, and results are highly reproducible. Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia, PA.     

Tribochemical reaction of Si-DLC coating in water studied by stable isotopic tracer

Tribochemical reaction of Si-DLC coating in water was investigated by stable isotopic tracer. Heavy water (deuterium oxide, D₂O) was used to carry out the friction test of the coating against a 440C ball. The worn surfaces were analyzed by ToF-SIMS. The results showed that tribochemical reaction of Si-DLC occurred with D₂O, and CD, OD groups were formed on the contact surfaces. The formation of SiOD and CO₂D groups was also confirmed on the worn ball surface. The tribochemical products containing hydrophilic hydroxyl and carboxyl groups are considered to be responsible for low friction and wear of Si-DLC coating and the counter part in a water environment. On the other hand, the Si amount of the coating decreased due to the rubbing. The decrease in the Si amount was not only caused by the removal of the surface layer in which Si concentrated, but also by the tribochemical reaction. The presence of Si may accelerate the tribochemical reaction resulting in the lower friction and the wear of the counter ball, although the wear of the coating increases due to chemical wear, compared with Si-free DLC coating.     

Microstructural,mechanical and tribological properties of carbon nanotubes reinforced plasma sprayed molybdenum disulphide composite coatings

The development of 1-Dimensional (1D) and 2-Dimensional (2D) materials have gained considerable attention towards achieving solid-state lubricity. Herein, we present the effect of carbon nanotubes (1D) reinforcement into the molybdenum disulphide (2D) coatings. Plasma sprayed MoS₂ coatings reinforced with 2-4 wt% CNTs were fabricated using shroud plasma spraying over steel substrates. The shroud attachment envelops the plasma plume and cut down its exposure to surroundings, which minimizes the oxidation of MoS₂ powder during spraying. The microstructural analysis revealed the presence of MoS₂ and CNTs in the composite coating. The mechanical hardness and elastic modulus of MoS₂ coating improved by 2–3 folds in the composite coating. In tribological performance, the coefficient of friction (COF) decreased from 0.13 to 0.07 in M2C coating. The wear weight loss was estimated as 0.89 ± 0.07 mg, 0.18 ± 0.02 mg and 0.39 ± 0.03 mg for M, M2C and M4C coatings respectively. It can be attributed that tubular CNTs acted as bearing on MoS₂ layers. This work opens an impressive stepping for the synergistic mixture of 1D (CNTs) and 2D (MoS₂) material to obtain high-quality wear-resistant coatings.     

Mechanical and tribological properties of diamond-like carbon coatings films deposited from an electron cyclotron resonance plasma

The friction coefficients have been investigated in amorphous diamond-like carbon (DLC) films deposited by a dual ECR–r.f. method, as a function of r.f. substrate bias in relation with the H content and bonding. Combined infrared absorption, elastic recoil detection analysis and tribological tests are used to characterize fully the films in their as-deposited state. Friction coefficients (μ) of the coatings against sapphire balls are determined in air at room temperature. The results indicate clearly that the samples exhibit high compressive stresses and the friction coefficients are found to be low and are affected by the magnitude of the biaxial stress and the microstructure of the films.     

Microstructural,mechanical and tribological properties of nanostructured YSZ coatings produced with different APS process parameters

Plasma sprayed ceramic coatings can be used in turbine engines as thermal barrier or abradable coatings, in order to improve the durability of the components as well as the efficiency. The presence of nanostructures, deriving from partial melting of agglomerated nanostructured particles, represents an interesting technological solution in order to improve their functional characteristics. In this work nanostructured yttria stabilized zirconia (YSZ) coatings were deposited by air plasma spraying (APS). The influence of the main process parameters on their microstructural, mechanical and tribological properties was investigated by scanning electron microscopy (SEM), indentation techniques at micro- and nano-scale and wear tests, respectively. Their porous microstructure was composed of well melted overlapped splats and partially melted nanostructured areas. This bimodal microstructure led to a bimodal distribution of the mechanical properties. An increase of plasma power and spraying distance was able to produce denser coatings, with lower content of embedded nanostructures, which exhibited higher elastic modulus and hardness as well as lower wear rate.     

Mechanical and tribological properties of nano/micro composite alumina coatings fabricated by atmospheric plasma spraying

Adding nano particles can significantly improve the mechanical properties and wear resistance of thermal sprayed Al₂O₃ coating. However, it still remains a challenge to uniformly incorporate nano particles into traditional coatings due to their bad dispersibility. In the present work, nanometer Al₂O₃ (n-Al₂O₃) powders modified by KH-560 silane coupling agent were introduced into micrometer Al₂O₃ (m-Al₂O₃) powders by ultrasonic dispersion to afford nano/micro composite feedstock, and then four resultant coatings (weight fraction of n-Al₂O₃: 0%, 3%, 5% and 10%) were fabricated by atmospheric plasma spraying. The features and constitutes of feedstock and as-sprayed coatings, as well as their porosity, bonding strength, microhardness and frictional behaviors were investigated in detail. Results show that the nano/micro composite feedstock with uniform microstructure can be better melted in the spraying process, thereby obtaining coatings with denser microstructure, higher hardness and bonding strength. Added n-Al₂O₃ has no obvious effect on the friction coefficient of composite coatings, whereas can improve their wear-resistant and reduce the worn degree of counterpart. The wear mechanism of traditional coating is brittle fracture and lamellar peeling, while that of composite coating with weight fraction of n-Al₂O₃ of 10% is adhesive wear.     

Investigation of the tribological and biomechanical properties of CrAlTiN and CrN/NbN coatings on SST 304

This study examines the influence of thin layer coatings of CrAlTiN and CrN/NbN, deposited via physical vapor, on the biocompatibility, mechanical, tribological, and corrosion properties of stainless steel 304. The microstructure and morphology of the thin CrAlTiN and CrN/NbN layers were characterized by scanning electron microscopy (SEM), EDX, and X-ray diffraction. The pin on disc wear test was performed on bare and metal-nitride coated SST 304 under a 15 N load at 60 rpm and showed that the wear rates of the thin CrAlTiN and CrN/NbN film coatings were lower than the bare substrate wear ratio. The coefficients of friction (COFs) attained were 0.64, 0.5, and 0.55 for the bare substrate, CrN/NbN coating, and CrAlTiN coating, respectively. Nano indentation tests were also performed on CrAlTiN-coated and CrN/NbN-coated SST 304. The nanohardnesses and Young's moduli of the coated substrates were 28 GPa and 390 GPa (CrN/NbN-coated) and 33 GPa and 450 GPa (CrA1TiN-coated), respectively. For comparison, the nanohardness and Young's modulus of the uncoated substrate were 4.8 GPa and 185 GPa, respectively. Corrosion tests were conducted, and the behaviors of the bare and metal nitride-deposited substrates were studied in CaCl₂ for seven days. The corrosion Tafel test results showed that the metal-nitride coatings offer proper corrosion resistance and can protect the substrate against penetration of CaCl₂ electrolyte. The CrN/NbN-coated substrates showed better corrosion resistance compared to the CrAlTiN-coated ones. In evaluating the biocompatibility of the CrAlTiN and CrN/NbN coatings, the human cell line MDA-MB-231 was found to attach and proliferate well on the surfaces of the two coatings.     

Numerical identification of bulk behavior law of manganese phosphate coatings. comparison with tribological properties

The tribological properties of a manganese phosphate treatment are optimized with consideration of the process parameters and a thermal annealing before lubrication. The analysis was first realized through a friction test. This article deals with the application of a numerical identification procedure of coating bulk behavior to the studied cases. The mechanical properties of the chosen coatings are identified using Vickers microindentation. A plastic behavior law representing the coating and its neighboring substrate is identified using an inverse approach. The obtained bulk behavior law of the coating provides an accurate understanding of the performance of that coating. Many correlations are posited between the behavior laws, such as resistance to seizure and other characterization results, particularly SEM examination and coating weight. This knowledge leads to an objective optimization of the manganese phosphating process using finite element computation. CALFA, 1230 rue de l’Université, BP 819, 62408 Béthune, Cedex, France. Voice: 33.3.2163.2350; fax: 33.3.2168.4957; email: philippe.hivart@univ-artois.fr. Saint-Quentin-en-Yvelines, France. LAMIH, UMR CNRS 8530, France.