Graphite-like and Diamond-like Carbon Coatings with Exceptional Tribological Properties

THE PHYSICAL DEMANDS on engineeringcomponents are continually increasing whilstenvironmental controls on the use of lubricants becomemore and more restrictive.This has led to increasingdemand for high load bearing,solid lubricant coatingsthat enable engineered surfaces to rub against oneanother with reduced friction and wear.One of themost promising candidate coatings is diamond-likecarbon,DLC.However,the term DLC is used to describe a broadrange of carbon-based coatings that includes…     

Effect of Annealing Temperature on Tribological Properties and Material Transfer Phenomena of CrN and CrAlN Coatings

This study evaluates the effects of annealing temperature and of the oxides produced during annealing processes on the tribological properties and material transfer behavior between the PVD CrN and CrAlN coatings and various counterface materials, i.e., ceramic alumina, steel, and aluminum. CrAlN coating has better thermal stability than CrN coating in terms of hardness degradation and oxidation resistance. When sliding against ceramic Al₂O₃ counterface, both CrN and CrAlN coatings present excellent wear resistance, even after annealing at 800 °C. The Cr-O compounds on the coating surface could serve as a lubricious layer and decrease the coefficient of friction of annealed coatings. When sliding against steel balls, severe material transfer and adhesive wear occurred on the CrN and CrAlN coatings annealed at 500 and 700 °C. However, for the CrAlN coating annealed at 800 °C, much less material sticking and only small amount of adhesive wear occurred, which is possibly due to the formation of a continuous Al-O layer on the coating outer layer. The sliding tests against aluminum balls indicate that both coatings are not suitable as the tool coatings for dry machining of aluminum alloys.     

Optimum Me-DLC coatings and hard coatings for tribological performance

In this study, hard coatings (TiN, TiCN, CrN, and CrCN) and Me-DLC coatings (Ti _x%-C:H and Cr _x%-C:H) were deposited on tungsten carbide (WC) substrate by multiarc physical vapor deposition (MAPVD) and unbalanced magnetron (UBM) sputtering, respectively. Counterbodies of the AISI 1045 steel cylinder and the AA7075T651 aluminum cylinder were used in the cylinder-on-disk, line-contact wear mode under dry condition; a counterbody of the AISI 52100 steel ball was used in the ball-on-disk, point-contact wear mode, under both dry and lubricated conditions. All wear tests were conducted with a reciprocating machine. After the tests, the most suitable coating for various counterbodies and test environments was selected. For the coating/1045 steel cylinder, the Ti_10%-C:H coating possesses excellent tribological characteristics. For the coating/7075T651 aluminum cylinder, hard coatings display excellent wear resistance. For the coating/steel ball, CrCN and CrN coatings display very little wear under both dry and lubricated conditions. On TiN and TiCN coatings, special wear mechanisms of material transfer, adhesion wear, and fatigue fracture occurred during initial tests under kerosene lubrication.     

W含量对CrWN涂层在干摩擦和油润滑下的摩擦学性能影响

利用扫描电子显微镜、X射线衍射仪、纳米压痕仪、3D形貌仪和往复式摩擦磨损试验机考察了W含量对CrWN涂层在干摩擦和PAO润滑条件下的摩擦学性能影响。结果发现：随W含量的增加,利用离子束辅助沉积技术制备的CrWN涂层显微结构从致密柱状晶变成粗大柱状晶,再变成纤维状晶。硬度随W含量的增加先增大后减小,当W含量为9.96 at.%时硬度最大。CrWN涂层在干摩擦条件下的摩擦系数随W含量的增加先减小后趋于不变,但在PAO润滑条件下的摩擦系数随W含量的增加逐渐减小。干摩擦下, 掺少量W元素会加重CrN涂层试样及其对磨球的磨损;但W掺杂显著改善CrN涂层试样及其对磨球在PAO润滑条件下的耐磨性。     

20CrMo上沉积CrN涂层的力学性能及5W/40润滑下的摩擦学性能

在活塞销材料(20CrMo)上沉积了5种不同厚度的CrN涂层,研究其力学性能及发动机油5W/40润滑下的摩擦学性能。分别对CrN涂层的表面形貌、截面厚度、硬度、弹性模量和高温膜基结合性能进行了测试。探讨了不同接触压力和不同转速下CrN涂层与锡青铜(QSn7-0.2)配副以及基材20CrMo与QSn7-0.2配副在5W/40润滑下的摩擦学性能差异,并分析了接触电阻。结果表明:涂层沉积厚度对CrN涂层的硬度等力学参数的影响较小,但对高温膜基结合性能的影响较大。在5W/40润滑下,CrN涂层与QSn7-0.2配副在接触压力较大或较小的大部分区域都具有相对较低的摩擦因数,且磨损体积极小。     

有机钼添加剂作用下CrN和CrAlN涂层的摩擦学性能∗

CrN 和 CrAlN 涂层以其优异的力学性能可作为汽车发动机运动部件的保护性涂层使用,然而它与常用润滑油添加剂的相互作用仍需要进一步的研究。 采用磁控溅射技术制备氮化铬(CrN)和氮化铬铝(CrAlN)涂层,利用 X 射线衍射和纳米压痕研究涂层的微结构和机械性能,考察常用摩擦改进剂-烷基二硫代氨基甲酸钼(MoDTC)对涂层摩擦学性能的影响,并通过电子扫描电镜和 X 射线光电子能谱技术等表征探究 MoDTC 的减摩作用机制。 结果表明:与 CrN 涂层相比,CrAlN 涂层结构致密,晶粒细化,机械性能更好。 在添加质量分数为 1%的 MoDTC 后的 PAO 基础油润滑下,表现出更优异的减摩抗磨性能。 对磨痕表面的 XPS 分析表明,在边界润滑条件下,钢/ CrN 和钢/ CrAlN 摩擦运动过程中 MoDTC 均发生化学降解反应,生成一层含二硫化钼(MoS₂ )的润滑膜,且后者产生的 MoS₂ 含量更高,因而表现出更优的摩擦学性能。 研究结果对延长汽车发动机的使用寿命具有指导意义。     

不同工作环境下CrN涂层的摩擦磨损性能

为探索研究CrN硬质涂层材料在复杂工况条件下的使用特性,采用多弧离子镀技术在304不锈钢基板表面沉积CrN薄膜,并分析了其在不同工作环境下的摩擦磨损性能。采用X射线衍射仪(XRD)分析了薄膜的相结构,采用冷场发射扫描电子显微镜(FESEM)观察了薄膜的微观形貌,并用其能谱分析(EDS)功能分析了磨痕磨粒的化学成份,采用纳米压痕仪和纳米划痕仪测试了薄膜的机械性能。摩擦试验研究结果表明,在干摩擦环境中,随氧分压增高,CrN薄膜摩擦因数和钢球磨损率均增大,说明粘着磨损和氧化反应形成第三体磨粒磨损应是CrN薄膜发生破坏的主要原因;在真空环境中,CrN薄膜的摩擦因数维持在0.3左右;增大工作环境湿度,CrN薄膜的摩擦因数降低;在去离子水浸润环境中其摩擦因数可降低至0.1左右,说明CrN薄膜可应用于高湿度环境或真空环境中的减摩抗磨防护。     

Synthesis and characterization of multilayer CrN/ZrN coatings

In this study, multilayer CrN/ZrN coatings with various bi-layer periods (δ) were deposited by closed-field unbalanced magnetron sputtering and their compositions, crystalline structures and morphologies were characterized by auger electron spectroscopy (AES), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Additionally, the mechanical properties of the coatings were characterized by nano-indentation and wear tests. The XRD results showed that the diffraction peak of multilayer CrN/ZrN coatings is observable between the CrN (111) and the ZrN (111). This peak has a strong tendency to increase the intensity and sharpen the width as the substrate rotation speed increases, indicating that the grain size of the multilayer CrN/ZrN coatings gradually increases. The hardness of films was dependent on the bi-layer period (δ), and the maximum hardness and elastic modulus were approximately 31.8 GPa and 321.5GPa, respectively. Moreover, the results of the wear tests showed that the multilayer CrN/ZrN coatings exhibited greatly improved wear resistance compared to the monolithic CrN coatings.     

Erosion wear of CrN,TiN, CrAlN,and TiAlN PVD nitride coatings

Four nitride coatings (CrN, ZrN, CrAlN, and TiAlN) were deposited on YT15 cemented carbide by cathode arc-evaporation technique. Microstructural and fundamental properties of these nitride coatings were examined. Erosion wear tests were carried out, the erosion wear of these nitride coatings caused by abrasive particle impact was compared by determining the wear depth and the erosion rates of the coatings. The wear surface features were examined by scanning electron microscopy. Results showed that the coatings with Al (CrAlN and TiAlN) exhibited higher erosion wear resistance over those without Al (CrN and TiN). The H³/E² of the coating seemed to play an important role with respect to its erosion wear in erosion tests. AlTiN and CrAlN coatings being with high H³/E² exhibited lower erosion rates, while CrN coating with low H³/E² showed higher erosion rates under the same test conditions. Analysis of eroded surface of the coatings demonstrated that the TiN and CrN coatings exhibited a typical brittle fracture induced removal process, while AlTiN and CrAlN coatings showed mainly micro cutting and cycle fatigue fracture of material removal mode.     

The structure and properties of chromium nitride coatings deposited using dc, pulsed dc and modulated pulse power magnetron sputtering

The time averaged ion energy distributions and ion fluxes of continuous dc magnetron sputtering (dcMS), middle frequency pulsed dc magnetron sputtering (PMS), and modulated pulse power (MPP) magnetron sputtering plasmas were compared during sputtering of a Cr target in an Ar/N₂ atmosphere in a closed field unbalanced magnetron sputtering system. The results showed that the dcMS plasma exhibited a low ion energy and ion flux; the PMS plasma generated a moderate ion flux of multiple high ion energy regions; while the MPP plasma exhibited a significantly increased number of target Cr⁺ and gas ions with a low ion energy as compared to the dcMS and PMS plasmas. Cubic CrN coatings were deposited using these three techniques with a floating substrate bias. The structure and properties of the coatings were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nanoindentation, microscratch and ball-on-disk wear tests. It was found that the deposition rate of the MPP CrN depositions was slightly lower than those of the dcMS depositions, but higher than in the PMS depositions at similar average target powers. The coatings deposited in the dcMS and PMS conditions without the aid of the substrate bias exhibited large columnar grains with clear grain boundaries. On the other hand, the interruption of the large columnar grain growth accompanied with the renucleation and growth of the grains was revealed in the MPP CrN coatings. The MPP CrN coatings exhibited a dense microstructure, fine grain size and smooth surface with high hardness (24.5 and 26 GPa), improved wear resistance (COF = 0.33 and 0.36) and adhesion, which are the results of the low ion energy and high ion flux bombardment from the MPP plasma.     

Improvement of the tribological behaviour of PVD nanostratified TiN/CrN coatings — An explanation

A hard TiN/CrN multilayered coating, consisting of alternating nanometer scale TiN and CrN layers (bilayer period of 40 nm), was deposited by arc evaporation process on M2 tool steel. Monolayered TiN and CrN are also deposited in the same conditions, and used as references. In order to get a better understanding of the tribological behaviour of coated parts, two types of experiments were performed. The dry-sliding wear resistance was evaluated with a ball-on-disk tribometer, while surface fatigue resistance was determined by a cyclic multi-impact test. The architecture of layers is measured by XRD and observed by TEM. The residual stress field was characterised using XRD and the sin²ψ method at a synchrotron radiation facility.All coatings present a columnar microstructure. TiN demonstrated better wear resistance than CrN and this characteristic is still increased two times by using the nanostratified coating. In the same way, the results of surface oligo-cyclic fatigue test confirm the high performance of the nanostructured coating with respect to the monolayered ones. The differences in mechanical properties of coatings evaluated through nanoindentation measurements do not lead to a direct correlation with the tribological results, and therefore cannot explain such differences. Moreover, a microscopic analysis of the samples after both tribological tests reveals two opposite cracking mechanisms. Monolayered TiN and CrN are subjected to a transversal crack propagation until the peeling of the coating, whereas the multilayered coating only undergoes cohesive cracks deviated in the TiN/CrN interface zones. Both opposite behaviours are the consequence of the distribution of stresses along the thickness of the film.     

润滑条件下WC-CoCr涂层的磨损行为

研究了在润滑条件下,WC-CoCr涂层与SiC摩擦副对磨时的摩擦和磨损性能,分析了加载载荷和润滑条件(干摩擦、润滑脂、金刚石研磨膏)对WC-CoCr涂层摩擦系数和磨损量的影响规律,对涂层的磨损机理进行了探讨。实验结果表明:脂润滑时,WC-CoCr涂层与SiC摩擦副对磨时的摩擦系数和磨损率降为最小,其中摩擦系数基本在0.1左右波动;金刚石研磨膏润滑时,磨损率高达1.521 24×10-6 g/m,为干摩擦条件下的2.68倍,抗磨减摩效果不理想;干摩擦时,涂层表面存在硬挤压痕,主要磨损机制为微切削并伴随着塑性变形,而在金刚石研磨膏润滑条件下,三体磨粒磨损起主导作用。     

Tribological behavior of CrN/WN multilayer coatings grown by ion-beam assisted deposition

CrN monolayer coating and CrN/WN multilayer coatings were deposited on the silicon (100) substrate by ion-beam assisted deposition process. The bilayer period of these coatings was controlled at 8 nm and 30 nm. The cross-sectional morphology of nanoscaled multilayer coatings was characterized by scanning electron microscopy and transmission electron microscopy. The wear resistance of CrN/WN multilayer coatings and CrN monolayer coating was investigated using a pin-on-disc tribometer. The surface roughness (Ra) of the coatings was evaluated by atomic force microscopy, and that of CrN and WN monolayer coating was 6.7 and 5.9 nm, respectively. The employment of multilayer configuration in CrN/WN coating with bilayer period of 8 nm and 30 nm effectively reduced the surface roughness down to 1.9 and 2.2 nm, respectively. The friction coefficient of CrN monolayer coating and CrN/WN multilayer film with a bilayer period of 30 nm was 0.63 and 0.31, respectively. Owing to the high hardness/elastic modulus ratio, as well as the dense structure and the smooth surface roughness, the CrN/WN multilayer coatings exhibited better wear resistance in the consideration of friction coefficient and the worn surface morphology.     

Tribological testing of commercial CrN, (Ti,Al)N and CrC/C PVD coatings — Evaluation of galling and wear characteristics against different high strength steels

The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with galling in sheet metal forming operations. Galling is a tribological phenomenon associated with transfer of material from the steel sheet to the tool surface during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency of galling in sheet metal forming, including the development of new dry lubricants, new forming tool steel grades and improved surface engineering treatments such as the deposition of low friction CVD- and PVD-coatings. In the present study the potential performance of three commercial PVD coatings, including CrN, (Ti,Al)N and a CrC/C DLC-based coating, in the forming of hot and cold rolled high strength steel as well as electro and hot-dip galvanized high strength steel has been evaluated using pin-on-disc testing under lubricated contact conditions. Post-test examination of the tribosurfaces using FEG-SEM and EDS analyses was performed in order to evaluate the mechanisms controlling the tendency to material transfer and wear. The results show that in contact with the hot and cold rolled steel the material pick-up tendency of the PVD coatings tend to increase in the order CrC/C-CrN-(Ti,Al)N while in contact with the two galvanized steel sheets, the CrC/C and the (Ti,Al)N coating show a significantly lower material pick-up tendency as compared with the CrN coating. Further, the substrate hardness has a strong influence on the wear of the PVD coatings and consequently on the friction characteristics and galling tendency of the coating/substrate composite. Low substrate hardness, resulting in a low load bearing capacity, increases the tendency to cracking and subsequently chipping of the brittle coating.     

离子束增强沉积CrN膜层及其微动摩擦学性能研究

以不同氮离子辅助轰击能量制备CrN膜层．利用纳米压入仪及显微硬度计分别测试单晶Si片上膜层的硬度及断裂韧度K1C．使用XRD、XPS及EPMA分析离子轰击能量对镀层组织结构的影响。结果表明，采用能量较低的氮离子轰击得到的涂层，由于金属Cr的存在，涂层硬度虽有所降低，但断裂韧度K1C数值较高。选择较低的4keV辅助轰击能量，在M2高速钢基体上沉积CrN涂层，膜层在空气介质中表现出优异的耐磨减摩特性.但在水介质条件下，由于膜层接触区域的去钝化，再钝化使腐蚀和磨损相互加速，导致CrN膜层摩擦系数，尤其是磨损量明显高于基材。     

Effect of a multilayer structure and lubrication on the tribological properties of coatings of Fe-W alloys

The methods for expanding the use of nanocrystalline electrolytic Fe-W alloys by creating a multilayer structure and using oil lubrication were studied. It was shown that lubricants can reduce the coefficient of friction and oxygen penetration into the sliding pairs, thus enhancing the wear resistance behaviour of Fe- W coatings as compared to that at dry friction, when the surface tribo-oxidation dominates. The electrodeposition of multilayer Fe-W/Cu coatings from a single bath was shown to be feasible. The tribological and mechanical properties of such coatings were investigated. The multilayer structure was found to improve the wear resistance characteristics of the coatings even at dry friction and at a relatively high normal load of 10 N.     

High rate deposition of thick CrN and Cr2N coatings using modulated pulse power (MPP) magnetron sputtering

As a variation of high power pulsed magnetron sputtering technique, modulated pulse power (MPP) magnetron sputtering can achieve a high deposition rate while at the same time achieving a high degree of ionization of the sputtered material with low ion energies. These advantages of the MPP technique can be utilized to obtain dense coatings with a small incorporation of the residual stress and defect density for the thick coating growth. In this study, the MPP technique has been utilized to reactively deposit thick Cr₂N and CrN coatings (up to 55 μm) on AISI 440C steel and cemented carbide substrates in a closed field unbalanced magnetron sputtering system. High deposition rates of 15 and 10 μm per hour have been measured for the Cr₂N and CrN coating depositions, respectively, using a 3 kW average target power (16.7 W/cm² average target power density), a 50 mm substrate to target distance and an Ar/N₂ gas flow ratio of 3:1 and 1:1. The CrN coatings showed a denser microstructure than the Cr₂N coatings, whereas the Cr₂N coatings exhibited a smaller grain size and surface roughness than those of the CrN coatings for the same coating thickness. The compressive residual stresses in the CrN and Cr₂N coatings increased as the coating thickness increased to 30 μm and 20 μm, respectively, but for thicker coatings, the stress gradually decreased as the coating thickness increased. The CrN coatings exhibited an increase in the scratch test critical load as the thickness was increased. Both CrN and Cr₂N coatings showed a decrease in the hardness and an increase in the sliding coefficient of friction as the coating thickness increased from 2.5 to 55 μm. However, the wear rate of the CrN coatings decreased significantly as the coating thickness was increased to 10 μm or higher. The 10-55 μm CrN coating exhibited low wear rates in the range of 3.5-5 × 10⁻⁷ mm³ N⁻¹ m⁻¹. To the contrary, the Cr₂N coating exhibited relatively low wear resistance in that high wear rates in the range of 3.5 to 7.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹ were observed for different thicknesses.     

Micro-scale Abrasion and Medium Load Multiple Scratch Tests of PVD Coatings

THIN film coatings such as titanium nitride(TiN)orDiamond Like Carbon(DLC)are commonly used toprovide wear resistance to tools and mechanicalcomponents.Many tests have been developed to assesstheir characteristics;these tests can determine thehardness,the adhesion and the wear resistance of thecoatings;they can be performed as part of a QualityControl(QC)procedure or as a way of investigating thecoatings properties.As wear by abrasion is an important cause of wearproblems in industry and…     

Tribological behaviour of pulsed magnetron sputtered CrB2 coatings examined by reciprocating sliding wear testing against aluminium alloy and steel

Among the number of attractive properties that transition-metal diborides (TiB₂, CrB₂, etc.) possess, high resistance to wear and chemical inertness are the most important when considering diboride coatings for dry machining of nonferrous materials, such as aluminium and its alloys. Due mostly to the problematic deposition of chromium diboride (preparation of targets, target cracking during the deposition process, control of stoichiometry etc.), these coatings remain comparatively less studied than, for example, titanium diborides, regarding their tribological performance.In this paper we report on the tribological behaviour of pulsed magnetron sputtered (PMS), smooth and fully dense, crystalline, 21-38 GPa hard CrB₂ coatings examined by reciprocating sliding wear testing in ambient air (20 ± 2 °C, 20-30% humidity) against EN AW-2017A aluminium alloy and AISI 52100 chrome steel. The results are compared to those of pulsed magnetron sputter deposited TiN and CrN coatings. It is demonstrated that pulsed magnetron sputtered chromium diboride coatings exhibit the best tribological performance, in terms of amount of aluminium adhered on the surface of the wear track, during testing against aluminium alloy. When slid against AISI 52100 steel PMS CrB₂, CrN and TiN coatings exhibited coefficients of friction of 0.6, 0.6-0.7 and 0.43-0.45 respectively. The tribological behaviour of coatings was found to be dependent on the transfer film formation and its properties. Wear rates were up to ten times lower for pulsed magnetron sputtered CrB₂ coatings, compared to DC sputtered Cr-B films.     

Tribological behavior of TiN and CrN coatings sliding against an epoxy molding compound

TiN and CrN coatings were deposited by unbalanced magnetron sputtering, and then rubbed against an epoxy molding compound (EMC). In sliding against an EMC, TiN exhibited an extremely high wear rate and a low friction coefficient, while the CrN-coated sample showed the opposite behavior. To understand this difference, Raman spectroscopy and thermal testing were used to study both coatings. Combining the results of oxidation, Raman spectroscopy and tribological testing, it can be concluded that the oxidation and pore generation occurring in the TiN coating during sliding deteriorated the mechanical properties of the coating and therefore its wear resistance. The excellent wear performance of the CrN coating against EMC was related to its good oxidation resistance, and adhesion to the substrate at high temperature.