Thermal stability of superhard Ti-B-N coatings

Ternary transition-metal boron nitride Ti-B-N offers outstanding hardness and thermal stability, which are increasingly required for wear resistant applications, as the protective coatings are subjected to high temperature, causing thermal fatigue. Ti-B-N coatings with chemical compositions close to the quasibinary TiN-TiB₂ tie line and boron contents below ∼ 18 at.% contain a crystalline supersaturated NaCl structure phase, where B substitutes for N. Annealing above the deposition temperature causes precipitation of TiB₂, which influence dislocation mobility and hence the hardness of TiB_0.40N_0.83 remains at a very high level of ∼ 43 GPa with annealing temperature T_a up to 900 °C. Growth of Ti-B-N coatings with B contents above ∼ 18 at.% results in the formation of nm sized TiN and TiB₂ crystallites embedded in a high volume fraction of disordered boundary layer. The compaction of this disordered phase during annealing results in a hardness increase of TiB_0.80N_0.83 coatings from the as-deposited value of ∼ 37 GPa to ∼ 42 GPa at T_a = 800 °C. Excess B during growth of TiB_2.4 coatings causes the formation of bundles of ∼ 5 nm wide TiB₂ subcolumns encapsulated in a B-rich tissue phase. This nanocolumnar structure is thermally stable up to temperatures of ∼ 900 °C, and consequently the hardness remains at the very high level of ~ 48 GPa, as nucleation and growth of dislocations is inhibited by the nm sized columns. Furthermore, the high cohesive strength of the B-rich tissue phase prevents grain boundary sliding.     

Tribological behavior of a TiSiCN coating tested in air and coolant

One TiSiCN coating and one TiN coating as a comparison basis were investigated in this paper. The coatings were deposited on stainless steel substrates using a Plasma Enhanced Magnetron Sputtering (PEMS) process, a variation of the physical vapour deposition (PVD) technique. The XRD pattern for the TiSiCN coating implied that the coating either consists of TiN and TiC phases or C be incorporated in TiN as a single solid solution. Both coatings exhibited good adhesion, although their thickness (17 μm-45 μm) was much larger than that of many commercial PVD coatings. The TiSiCN coating showed higher hardness than the TiN coating. The sliding tribological behavior of the coatings against alumimium and alumina counterparts was studied both in air and in a coolant (Hangsterfer's S-500) by pin-on-disc tests. Scanning electron microscopy (SEM) was used to examine the wear tracks on the discs and the wear scars on the pins. Compared to the TiN coating, the TiSiCN coating exhibited lower wear rates and lower coefficients of friction (C.O.F.) against those two kinds of counterparts when tested in air. The cutting coolant provided a lubricant effect and reduced the adhesive wear and C.O.F. between the coating and the counterpart.     

TiN及TiSiN涂层在海水环境下的摩擦学行为研究

目的对比研究海水环境下Ti N及Ti Si N涂层与Al2O3对磨的摩擦磨损行为。方法采用多弧离子镀技术在316L不锈钢及单晶硅片上制备Ti N及Ti Si N涂层。利用场发射扫描电子显微镜(SEM)、X射线衍射仪(XRD)及X射线光电子能谱仪(XPS)分析了涂层的截面形貌及化学组织成分。选择纳米压痕仪测量了Ti N及Ti Si N涂层的硬度及弹性模量,使用UMT-3往复式摩擦试验机研究了人工模拟海水环境下Al2O3与Ti N及Ti Si N涂层对磨后的摩擦磨损行为,并采用扫描电镜(SEM)、电子能谱(EDS)及表面轮廓仪来深入分析了磨痕的摩擦磨损情况。结果研究表明,Ti N涂层的硬度为32.5 GPa,当Si元素掺入涂层以后,Ti Si N涂层的硬度提高到了37 GPa。同时,较之于Ti N涂层,Ti Si N涂层的腐蚀电流密度下降了一个数量级。在摩擦实验中,Ti N涂层的摩擦系数和磨损率分别为0.35和5.21×10-6 mm3/(N·m),而Ti Si N涂层的摩擦系数和磨损率均有明显下降,分别为0.24和1.96×10-6 mm3/(N·m)。结论 Si元素掺杂后能显著提高Ti N涂层在海水环境下的摩擦学性能,主要归因于结构的致密,硬度、韧性、抗腐蚀性的提高及润滑相的形成。     

Structure-property-performance relations of high-rate reactive arc-evaporated Ti-B-N nanocomposite coatings

This study demonstrates the successful synthesis of hard and wear resistant nanocomposite Ti-B-N coatings by high-rate reactive arc-evaporation from Ti/B compound targets in a commercial industrial-sized deposition chamber. Morphological investigations by profilometry and scanning electron microscopy indicate that the coatings exhibit a lower droplet density as compared to a TiN reference as well as a compositionally graded multilayer structure. These results will be related to the previously reported microstructural characterization, which revealed a highly stressed nanocrystalline TiBN solid solution formed at lower N₂ fractions and a stable TiN/(amorphous) BN dual-phase structure obtained at higher N₂ partial pressures. Emphasis is further laid on mechanical and tribological characterization. A maximum hardness of 34.5 GPa is detected for the TiBN solid solution decreasing to 24 GPa for the coatings containing approximately 30-40 vol.% amorphous BN. The maximum in hardness coincides with the minimum in wear, while the coefficient of friction is fairly constant at 0.7-0.8.     

TiSiN nanocomposite coatings by chemical vapor deposition in a fluidized bed reactor at atmospheric pressure (AP/FBR-CVD)

TiSiN nanocomposite coatings were deposited on stainless steel by chemical vapor deposition in a fluidized bed reactor at atmospheric pressure (AP/FBR-CVD) by reaction of TiCl₄ and SiCl₄ with NH₃ at 850 °C. Coatings were characterized by means of GD-OES, XPS and XRD. TiSiN coatings with a Si content of 9 at.% showed a hardness of 28 GPa (the hardness of TiN and SiN_x coatings was around 21 GPa) and a lower oxidation rate under dry air at 600 °C. Our results show for the first time that AP/FBR-CVD can be tuned for the deposition of nanocomposite ceramic coatings.     

Mechanical and tribological properties of TiN/Ti multilayer coating

A large area filtered arc deposition (LAFAD) technique was used to deposit TiN/Ti multilayer coatings with fixed TiN layer thickness and different Ti layer thickness. Nanoindention and pin-on-disk tribometer were used to characterize the hardness, elastic modulus, plasticity, friction coefficient, and wear rate of the multilayer coatings. The dependence of the mechanical and tribological properties of the coating on the Ti interlayer thickness was systematically studied. It was found that the increase in the Ti layer thickness resulted in a decrease in the effective hardness and elastic modulus, and an increase in the wear rate, plasticity, and toughness. The coatings with a Ti layer thicknesses of 0, 25 nm and 50 nm possess an excellent combination of high effective hardness (> 20 GPa), high plasticity (> 69%), low friction coefficient, and high wear resistance.     

High-temperature tribological properties of CrAlN, CrAlSiN and AlCrSiN coatings

Cr-Al-Si-N coatings with high and low Cr/Al ratios (CrAlSiN and AlCrSiN, respectively) were deposited on WC substrates by cathodic arc and compared with a reference Cr-Al-N coating. The silicon content was close to 3 at.%. X-ray diffraction analysis showed that CrAlN and CrAlSiN coatings exhibited the cubic Cr(Al)N structure, whereas in AlCrSiN a mixture of cubic Cr(Al)N and wurtzite-type AlN was identified. All three coatings showed excellent thermal stability and oxidation resistance up to 800 °C. The tribological properties were evaluated by ball-on-disk tribometer in the temperature range 25-600 °C. Two materials were used as counterparts: alumina and 440C steel. Sliding against 440C steel balls led to the extensive wear of the balls and transfer of the ball material to the surface of the coatings. The coatings were not damaged. When sliding against alumina balls, the coating wear was low up to testing temperature 300 °C. At 400 °C, CrAlSiN coating was partially worn through. CrAlN and AlCrSiN coatings were almost immediately worn out at 600 °C. The analysis of the wear debris identified high-temperature adhesive failure of the coatings.     

Characterization and wear properties of nanoscaled TiN/TaN multilayer coatings

The structural, morphological, mechanical and tribological characterization of nanoscaled multilayer TiN/TaN coatings deposited by magnetron sputtering technology were investigated by low angle X-ray diffractometry, high angle X-ray diffractometry, atomic force microscopy, microhardness, pin-on-disc testing and 3-D surface profiler. The results show that the TiN/TaN coatings exhibit good modulation period and sharp interface between TiN and TaN layers. In mutilayered TiN/TaN coatings, TiN layers have cubic structure, but hexagonal structure emerged among TaN layers besides cubic structure as modulation period is beyond 8.5 nm. The mierohardness is affected by modulation period and the maximum hardness value of 31.5 GPa appears at a modulation period of 8.5 rim. The coefficient of friction is high and the wear resistance is improved for TiN/TaN coatings compared with those of TiN coating; the wear mechanism exhibits predominantly ploughing, material transfer and localized spallation.     

Nanoscratching deformation and fracture toughness of electroless Ni-P coatings

In the present investigation electroless Ni-P coatings were prepared. Structural characterizations indicated that the as-deposited coating had an amorphous structure with a P content of 23 at.%. The deformation behavior of an electrolessly amorphous Ni-P coating was investigated by using the Vickers indentation and the Tribo-indenter instrumented nano-indentation technique. The hardness of the Ni-P coating is remarkably improved after proper heat-treatment and the hardness is as high as 12.7 GPa for the coating annealed at 400 °C for 1 h. However, the cracks were observed during the indentation of the Ni-P coatings annealed at 400 °C and 500 °C for 1 h. The corresponding fracture toughness was evaluated as 2.58 MPa m^0.5 and 1.33 MPa m^0.5, respectively. Nanoscratching tests indicated that the wear resistance of the Ni-P coatings was improved significantly with an increasing ratio of hardness (H) to elastic modulus (E). It was observed that the friction coefficient increased from 0.083 ± 0.006 for the Ni-P coating annealed at 300 °C up to 1.337 ± 0.009 for the IF steel substrate, while the H/E simultaneously decreased from 0.084 (10.7/128) to 0.009 (1.85/200). The study revealed that the electrolessly amorphous Ni-P coating had offered better corrosion resistance than the Ni-P coatings after heat-treatment. An annealing temperature of 300 °C is preferentially suggested for the trade-off between the wear resistance property and anti-corrosion property of the Ni-P coating.     

Effects of relative humidity on tribological properties of boron carbide coating against steel

Boron carbide coatings of 100 nm thick were synthesized on silicon substrate by DC magnetron sputtering using B₄C target with a mixture of Ar and methane (CH₄ at 1.2 vol.%) as processing gases. Tribological properties of the coating were studied in relation to the effects of relative humidity (RH). Reciprocating wear tests using 3 mm diameter steel balls as a counterpart were carried out at three relative humidity conditions. Confocal microscopy was used to observe worn surfaces and the wear scars on the steel balls. Elemental composition of the coating and worn surfaces were characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy. The tribological properties of boron carbide coating slid against steel ball were strongly affected by relative humidity. Lower and steady friction coefficient and higher wear resistance for both the coating and the steel ball were achieved at higher relative humidity. At high RH, tribochemical reaction occurred in the sliding surfaces, forming boric acid and carbon in a graphitic form on the worn surface of coating and a soft layer on the ball surface. The formation of boric acid on boron carbide coating combined with graphite structure led to the low and stable friction of boron carbide coating in medium and high relative humidity conditions. Smooth layer was formed on the worn surface of the steel ball at high relative humidity due to the tribochemical reaction. Low and steady value of friction coefficient and reduction of wear loss of both steel ball and boron carbide coating were attributed to the formation of the soft layer.     

Friction and wear properties of TiN,TiAlN, AlTiN and CrAlN PVD nitride coatings

Four nitride coatings, TiN, TiAlN, AlTiN and CrAlN were deposited on YG6 (WC + 6 wt.% Co) cemented carbide by cathodic arc-evaporation technique. The friction and wear properties were investigated and compared using ball-on-disc method at high speed with SiC ball as a counter material. The tests were evaluated by scanning electron microscopy, X-ray diffractometer, energy dispersive X-ray, micro hardness tester and an optical profilometer. The results showed that TiN and TiAlN coatings presented lower friction coefficient and lower wear rate, and that high Al content AlTiN and CrAlN coatings didn't present better anti-wear properties in this test. Oxidation and abrasive wear were the main wear mechanism of TiN coating. In spite of the observation of micro-grooves and partial fractures, TiAlN possessed perfect tribological properties compared with the other coatings. High Al content increased the chemical reactivity and aroused severe adhesive wear of AlTiN coating. CrAlN coating presented better properties of anti-spalling and anti-adhesion, but abundant accumulated debris accelerated wear of the coating under this enclosed wear environment.     

Structure and tribological properties of AlCrTiN coatings at elevated temperature

In this study, we analyzed the high temperature tribological behavior of AlCrTiN coatings deposited on WC substrates by low cathodic arc technique. The coatings chemical composition, Al 31 at.%, Cr 16 at.%, Ti 7 at.% and N 46 at.%, and the bonding state were evaluated by X-ray photoelectron spectroscopy. The mechanical properties of the coatings were studied by scratch-test and nanohardness depth sensing indentation. The morphology of the coatings surface, ball scars, wear tracks and wear debris as well as the oxidized samples was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The structure was analyzed using X-ray diffraction (XRD). Wear testing was carried out using a high temperature tribometer (pin-on-disc) with alumina balls as counterparts. The evaluation of the friction coefficient with the number of cycles (sliding distance) was assessed at different temperatures and the wear rates of the coatings and balls were determined; the maximum testing temperature was 800 °C. The coating showed an excellent thermal stability and wear resistance. The friction reached a maximum at 500 °C and then decreased, whereas the wear rate was negligible up to 600 °C and increased significantly at higher temperatures.     

Dry sliding wear behavior of PVD TiN,Ti55Al45N,and Ti35Al65N coatings at temperatures up to 600 °C

Three PVD nitride coatings (TiN, Ti₅₅Al₄₅N, and Ti₃₅Al₆₅N) with different Al content were deposited on the cemented carbides by cathode arc-evaporation technique. Microstructural and fundamental properties of these nitride coatings were examined. The friction and wear behavior of these coatings were evaluated at temperatures up to 600 °C. The wear surface features of the test samples were examined by scanning electron microscopy. Results showed that the friction coefficient of these nitride coatings is different depending on the temperature. The friction coefficient of TiN coating increased with the increase of test temperature; while the friction coefficient of Ti₅₅Al₄₅N and Ti₃₅Al₆₅N coatings with the addition of Al decreased with the increase of test temperature. The Ti₅₅Al₄₅N and Ti₃₅Al₆₅N coatings exhibited higher wear resistance over the one without Al (TiN coating). The wear resistance of these nitride coatings at high temperature wear tests is significantly dependent on their tribological oxidation behavior. The Ti₅₅Al₄₅N and Ti₃₅Al₆₅N coatings with the addition of Al exhibited improved wear resistance as compared to the TiN coating, which was attributed to that their tribo-chemically formed Al₂O₃ exhibited better tribological properties than the TiO₂ of the latter.     

纳米复合Ti-B-N薄膜的结构和摩擦学性能

研究了射频等离了体辅助化学气相沉积（PCVD）技术获得的Ti-B-N薄膜的组织结构和力学性能。结果发现，B元素的加入使薄膜中出现TiN纳米晶和BN非晶（nc-TiN／a-BN）的复合结构，其硬度显著高于TiN薄膜，最高可达40GPa。用球盘式摩擦磨损实验考察了薄膜的磨损特性。结果表明：与TiN薄膜相比，Ti-B-N薄膜抗磨损性能有显著提高，磨损机制与TiN薄膜不同，摩擦系数较TiN稍高。     

Mechanical and tribological properties of duplex treated TiN, nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings deposited on 410 low alloy stainless steel

The use of hard and superhard nanocomposite (nc) coatings with tailored functional properties is limited when applied to low alloy steel substrates due to their low load carrying capacity. Specifically in this work, in order to enhance the performance of martensitic SS410 substrates, we applied a duplex process which consisted of surface nitriding by radio-frequency plasma followed by the deposition of single layer (TiN, nc-TiN/a-SiN_x or nc-TiCN/a-SiCN) or multilayer (TiN/nc-TiN/a-SiN_x, TiN/nc-TiCN/a-SiCN) coating systems prepared by plasma enhanced chemical vapor deposition (PECVD). We show that plasma nitriding gives rise to a diffusion layer at the surface due to diffusion of nitrogen and formation of the α-Fe and ε-Fe₂N phases, respectively, leading to a surface hardness, H, of 11.7 GPa, compared to H = 5 GPa for the untreated steel. Among the TiN, nc-TiN/a-SiN_x and nc-TiCN/a-SiCN coatings, the latter one possesses the highest H value of 42 GPa and the highest H³/E_r² ratio of 0.83 GPa. Particularly, the TiN/nc-TiCN/a-SiCN multilayer coating system exhibits superior tribological properties compared to single layer TiN and multilayer TiN/nc-TiN/a-SiN_x coatings: this includes excellent adhesion, low friction (C_f = 0.17) and low wear rate (K = 1.6 × 10^− 7 mm³/N m). The latter one represents an improvement by a factor of 600 compared to the bare SS410 substrate. The significance of the relationship between the H/E and H³/E_r² ratios and the tribological performance of the nano-composite coatings is discussed.     

不同气氛下电火花沉积钛合金涂层的组织性能

分别在氮气、氩气和空气3种气氛下,在45钢上电火花沉积制备TC4钛合金涂层。利用OM、SEM、EDS、XRD、XPS等对钛合金沉积层的微观形貌、组织结构进行分析;利用纳米力学探针仪测试对比沉积层的力学性能;采用CETR摩擦磨损仪测试涂层的耐磨性。结果表明:氮气下电火花沉积生成含TiN及少量TiO和TiO2的陶瓷增强层。氮气中制取的涂层微裂纹较明显,但几无坑蚀和微孔,表面形貌优于氩气和空气下的沉积层。纳米硬度高达15.18GPa,无需增加沉积层厚度,即可获得较高硬度和抗变形能力。其摩擦因数为0.41,磨损量为2.2mg,均远低于45钢,也低于空气和氩气下制备的普通的钛合金涂层,并且改善了钛合金涂层的粘着磨损。     

Tribological performance of hybrid filtered arc-magnetron coatings. Part II: Tribological properties characterization

Nano-structured coating architectures were developed to provide a best blend of corrosion and wear resistance for high chromium content steels used in aerospace bearing and gear applications. A hybrid filtered arc-magnetron deposition process was employed to deposit functionally graded, multilayered and nanocomposite TiCrN/TiCrCN + TiBC cermet coatings on carburized steel substrates. Coatings exhibited excellent adhesion to the carburized surfaces and had hardness in the range of 23-25 GPa. Tribological properties of the coatings were characterized by: pin-on-disk COF, lubricated sliding, reciprocating sliding, and 3 ball half thrust bearing tests in dry and lubricated environments at high contact stresses. Both polyester and perfluoropolyalkylethers (PFPAE) based lubricants were used to evaluate coating performance with neutral and chemically aggressive lubrication. Sliding friction and reciprocating sliding wear tests were performed using modified disk-on-ring and point-on-disk arrangements, respectively. Contact stresses were estimated using the Hertzian contact formula (sliding friction), and through direct measurements of contact areas by SEM (reciprocating sliding). Low-speed thrust bearing high load rolling contact was evaluated at 350 °C, using Si₃N₄ balls and PFPAE-based lubricant, at contact stresses of ∼ 3.2 GPa. Aggressive corrosion testing was performed on coated samples using MIL-STD-810F “salt-fog” testing. Wear and corrosion behavior was investigated using SEM/EDS, EDX, AFM, profilometry, and optical microscopy. The influence of coating architecture on wear properties was investigated. Multifold improvements in the surface dry and lubricated wear life, reduction of the dry friction coefficient, prevention of corrosion attack from the products of PFPAE lubricant degradation, and improvement of salt-fog corrosion resistance are demonstrated.     

Effect of TiN/Ti composite coating and shot peening on fretting fatigue behavior of TC17 alloy at 350 °C

A TiN/Ti composite coating has been prepared on a TC17 titanium alloy substrate by an ion-assisted arc deposition (IAAD) technique with a view to improving the fretting fatigue resistance of the titanium alloy at 350 °C. The composition distribution, bonding strength, micro-hardness, ductility, tribological properties, and fretting fatigue resistance at elevated temperature of the coating have been investigated. The results indicate that the IAAD technique can be used to prepare a TiN/Ti composite coating with high hardness, good ductility, excellent bonding strength, and high load-bearing capability. The TiN/Ti composite coatings can improve the resistance to wear and fretting fatigue of the Ti alloy, as manifested in its excellent tribological behavior at 350 °C. However, the fretting fatigue resistance of the titanium alloy treated by shot peening (SP) combined with IAAD TiN/Ti coating post-treatment was lower than that by IAAD TiN/Ti coating or SP alone, because the compressive residual stress induced by SP was significantly relaxed during coating process and the coating easily cracked and broke off.     

Internal stress in TiAlBN at high temperatures

Hard TiAl(B)N coatings were deposited by radio-frequency magnetron sputtering in reactive mode in an argon and nitrogen environment using a TiAlB target with 12 at.% of boron. The deposition was carried out under ion bombardment at various negative bias voltages in the range of 0 to 170 V, and at substrate temperatures between 453 and 523 K. The internal stress in the coatings was studied at room temperature as a function of annealing temperatures in ambient air up to 1123 K. The heating duration was 2 h followed by annealing for 1 h. The microstructure, phase composition and hardness were also studied prior to and after annealing.We found that the TiAlBN coatings consist of TiAl₃ and TiN phases. With increasing ion bombardment, the structure of the coatings changes from columnar to nano-scale features. Prior to annealing we also observed a correlation between the residual stress and hardness. After annealing, the compressive stresses of the TiAl(B)N coatings decreased from 1.0 GPa to less than 0.2 GPa, while the hardness remained constant or increased from ∼ 10 GPa to ∼ 25 GPa. The hardness increase of the coatings after annealing is related to a self-hardening effect.     

A comparative study of reactive direct current magnetron sputtered CrAlN and CrN coatings

Approximately 1.5 μm thick CrN and CrAlN coatings were deposited on silicon and mild steel substrates by reactive direct current (DC) magnetron sputtering. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy (XPS). The surface morphology of the coatings was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD data showed that the CrN and CrAlN coatings exhibited B1 NaCl structure. Nanoindentation measurements showed that as-deposited CrN and CrAlN coatings exhibited a hardness of 18 and 33 GPa, respectively. Results of the surface analysis of the as-deposited coatings using SEM and AFM showed a more compact and dense microstructure for CrAlN coatings. The thermal stability of the coatings was studied by heating the coatings in air from 400 to 900 °C. The structural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data revealed that CrN coatings got oxidized at 600 °C, whereas in the case of CrAlN coatings, no detectable oxides were formed even at 800 °C. After annealing up to 700 °C, the CrN coatings displayed a hardness of only about 7.5 GPa as compared to CrAlN coatings, which exhibited hardness as high as 22.5 GPa. The potentiodynamic polarization measurements in 3.5% NaCl solution indicated that the CrAlN coatings exhibited superior corrosion resistance as compared to CrN coatings.