The effects of AlCrN coating,surface modification and their combination on the tribological properties of high speed steel under dry conditions

In this study, the effects of a combination of ultrasonic nanocrystalline surface modification (UNSM) technique and AlCrN coating on the tribological properties of high speed steel (HSS) were investigated. The AlCrN coating with a thickness of about 3 µm was deposited by the physical vapor deposition (PVD) technique onto the polished and UNSM-treated HSS specimens. The tribological and scratch tests results revealed that the AlCrN coating deposited onto the UNSM-treated specimen showed better tribological properties compared to that of the AlCrN coating deposited onto the polished specimen, which may be attributed to the modified surface beneath the AlCrN coating. Hence, it is expected that the results of this study can be applied to reduce the wear of fine blanking punches.     

Abrasive wear behavior of high speed steel and hard metal coated with TiAlN and TiCN

The wear behavior of M2 high speed HSS steel and WC hard metal coated with TiAlN and TiCN were investigated and compared, using the pin on disk standard test with different loads. The coating PVD process has been done by two different suppliers, using an industrial equipment unit with optimized conditions. The coated layers were measured and characterized. The load, sliding distance and velocity of 0.5 m/s were kept constant during the abrasion test in order to control these variables. The counterface disks used were electric steel sheets from three different suppliers. The lost volume and temperature at the pin end have been measured during the wear test. Comparisons of tribological performance for the coated HSS and hard metal were done, using a plot of lost volume versus sliding distance for substrates and coatings. The pin worn surfaces were observed using a scanning electron microscope. A significant increase in the wear resistance of M2 steel and WC hard metal when coated with TiAlN and TiCN was observed. Quality of these coatings depended upon the supplier. Excessive porosity has diminished the TiAlN counting wear resistance from one supplier. However, in general the performance of TiAlN is superior to TiCN. The pin wear rate depended on the disk microstructure.     

Improvement of the tribological properties of Al6061–T6 alloy under dry sliding conditions

The tribological properties of ultrasonic nanocrystalline surface modification (UNSM) treated Al6061–T6 alloy were investigated at various normal loads under dry sliding conditions. Electron backscattering diffraction (EBSD) analysis revealed a microstructure alteration of about 70 μm in thickness generated by the UNSM technique. The friction test results showed that the friction coefficient and wear rate of the UNSM-treated specimen reduced by about 25 and 20% compared to that of the UNSM-free specimen, respectively. X-ray photoelectron spectroscopy (XPS) results showed that the oxide percentage on the worn surface increased, but that of carbon percentage decreased after the UNSM treatment.     

Effect of heat treatment on wear behavior of HVOF thermally sprayed WC-Co coatings

A WC-17Co coating was deposited onto ST37 mild steel substrate using HVOF spray technique and then heat treated at different temperatures in a vacuum chamber. The coatings were then evaluated in the as sprayed and heat treated conditions. Inspections by SEM and phase analysis by XRD indicated that some brittle eta (η) phases were produced at high temperature heat treatments. Generation of these phases increased the coating's hardness and decreased fracture toughness of the coating. Tribological properties were studied under dry condition by using pin on disc machine and diamond metal matrix composite disc as counterface. Wear test results showed that as sprayed deposit had the best wear resistance and its wear mechanism was sharp cutting abrasion. The weight loss in heat treated samples increased by increasing heat treatment temperature and the wear mechanisms gradually changed from cutting to gouging abrasion.     

Friction and wear of polyphenylene sulfide composites filled with micro and nano CuO particles in water-lubricated sliding

The tribological behavior of polyphenylene sulfide (PPS) composites filled with micro and nano CuO particles in water-lubricated sliding condition were studied. Pin-on-disk sliding tests were performed against a steel counterface of surface roughness 0.09–0.11 μm. The lubrication regimes were established from friction data corresponding to various combinations of loads and sliding speeds. Later experiments were performed using the sliding speed of 0.5 m/s and contact pressure of 1.95 MPa, which corresponded to boundary lubrication regime. Micro CuO particles as the filler were effective in reducing the wear of PPS but nano CuO particles did not reduce wear. The steady state wear rate of PPS-30 vol.% micro CuO composite was about 10% of that of unfilled PPS and the coefficient of friction in this case was the lowest. The examination of the topography of worn pin surfaces of nano CuO-filled PPS by SEM revealed grooving features indicating three-body abrasion. The transfer films formed on the counterfaces during sliding were studied by optical microscopy and AFM. The wear behavior of the composites in water-lubricated sliding is explained using the characteristics of worn pin surfaces and transfer films on the counterface.     

链斗式卸料机链条的选材与耐磨性试验

笔者选用40Cr、55SiMnVB、60Si2Mn和65Mn作为链斗式卸料机链条材料,经过不同热处理后进行磨损对比试验,以验证它们在热处理后的耐磨性。碾压磨损试验和销盘磨损试验表明,55SiMnVB等温淬火和60Si2Mn钢淬火-回火试样的耐磨性较好,比原材料40Cr钢的耐磨性提高了1．4倍.     

Amorphous diamond coating of tungsten carbide and titanium carbonitride for erosive slurry pump component service

Tungsten carbide spray coatings have become well established for resisting abrasion and erosion in pumps used in conventional oil production and in oil sands operations. To achieve additional benefits from the extreme wear resistance of tungsten carbide its use is being extended to solid forms for some critical components. Slightly harder titanium carbonitride-based cermets have much lower density and coefficient of thermal expansion and for these reasons are being considered as an alternative to tungsten carbide. PVD amorphous diamond coating also has potential to further increase the service life of selected pump parts fabricated from solid cermets. Micro-abrasion testing and single scratch and nano-indentation evaluation have been carried out on non-coated and PVD amorphous diamond coated WC-4.8% TaC–4.5% TiC/6% Co–1% Cr and TiCN-17% WC/8% Mo materials. Data obtained illustrate that the tungsten–carbide based product has superior wear properties to the titanium carbonitride material and that PVD amorphous diamond coating of both cermets enhanced wear resistance significantly and displayed potential for successful service application.     

New tribometer designed for the characterisation of the friction properties at the tool/chip/workpiece interfaces in machining

This work deals with the development of a new tribometer designed for the characterisation of the frictional properties at the tool/chip/workpiece interfaces in cutting processes. Based on a plane–sphere contact configuration, the experimental set‐up enables a continuous regeneration of the pin–workmaterial contact. The average contact pressure can be selected up to 3 GPa under sliding velocities reaching 16 m/s. Under such severe conditions, which are not reachable with conventional tribometers, the apparent friction coefficient is quantified in parallel to the heat flux transmitted to the pin. This new system has been applied to the characterisation of the frictional properties during the dry machining of a 27MnCr5 annealed steel with a carbide cutting tool. The influence of the sliding velocity and of an additional TiN layer deposited by PVD on the carbide pins has been investigated in dry conditions. It has been shown that the sliding velocity is the more influential parameter, followed by the coating. Copyright © 2007 John Wiley & Sons, Ltd.     

Sliding tribological behavior of AlCrN coating

The sliding tribological behavior of the PVD AlCrN coating against Si₃N₄ ball have been investigated by using the CETR multi-functional UMT-2 test system under two sliding conditions (bidirectional and unidirectional). Reciprocating sliding tests (bidirectional) were performed under varied normal loads (5, 10 and 20 N) at sliding velocity of 0.48 m/min. Ball-on-disc tests (unidirectional) were performed at varied sliding velocities (0.48 and 5 m/min) under normal load of 5 N. The wear scars of the coating were evaluated by surface profilometer, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and the sliding wear mechanism of the coating was consequently discussed. The results showed that AlCrN coating had excellent anti-abrasion properties. Both the normal load in reciprocating sliding test and the sliding velocity in ball-on-disc test had significant influence on the sliding tribological behavior of the AlCrN coating. The combination of abrasion and oxidation was the main sliding wear mechanism for the AlCrN coating. The wear resistant and thermally stable oxides formed by the tribo-chemical reactions of chromium and aluminum protected the AlCrN coating against wear admirably.     

Synergy Effect of Ultrasonic Nanocrystalline Surface Modification and Laser Surface Texturing on Friction and Wear Behavior of Graphite Cast Iron

Laser surface texturing (LST) followed by an ultrasonic nanocrystalline surface modification (UNSM) process was applied to graphite cast iron to improve the friction and wear behavior. The surface hardness of the UNSM-treated and UNSM + LST-treated specimens was increased significantly compared to the polished and LST-treated specimens. The friction and wear behavior of the specimens was assessed using a ball-on-disk friction tester at an applied load of 10 N and a speed of 5 cm/s in both dry and lubrication conditions. The friction coefficient of the UNSM-, LST-, and UNSM + LST-treated specimens reduced in both dry and lubrication conditions compared to the polished specimen by 64, 30, and 64% and 63, 67, and 75%, respectively. In lubrication condition, the friction coefficient of the UNSM- and LST-treated specimens was further reduced by about 30 and 25% by UNSM + LST processes. In dry condition, the UNSM + LST-treated specimen exhibited a reduction in the friction coefficient of 46% compared to the LST-treated specimen, whereas no reduction in friction coefficient was found compared to the UNSM-treated specimen. The wear resistance of the UNSM-, LST-, and the UNSM + LST-treated specimens was enhanced by 22, 11, and 37% in the dry condition, respectively, whereas minuscule wear was observed in the lubrication condition that was difficult to quantify in our experiment. UNSM and LST processes were effectively combined to improve the friction and wear behavior of graphite cast iron.     

A study on the restoration method of friction, wear and fatigue performance of remanufactured crankshaft

Crankshaft translates reciprocating linear piston motion into rotation in internal combustion engine. So it receives complex combination of stresses. Therefore, crankshaft remanufacturing process is designed thoroughly with special attention to fatigue and tribological performance. Experimental study is carried out in order to show that UNSM (ultrasonic nanocrystal surface modification) technology which will be used as final surface treatment after 0.2 mm depth surface grinding, could restore original fatigue strength and tribological performance. Furthermore the feasibility steady to replace conventional overlay welding in crankshaft remanufacturing process by UNSM (ultrasonic nanocrystal surface modification) technology is carried out. Effects of UNSM technology are established through rotary bending test, rolling contact fatigue (RCF) test and wear simulation test. The test specimen used SCM435 material of crankshaft and commercial bush. The test result showed fatigue limit improved by 30% and RCF life increased by 40% for UNSM treated specimen. And friction coefficient decreased by 24% and wear amount decreased by 85%.     

Sliding friction and wear properties of CNX/TiN composite films

A combined dc magnetron sputtering and multi-arc deposition system was used to grow CN_X/TiN composite films on a high-speed-steel (HSS) substrate. The thickness of these films is about 3 μm, the hardness of the coating exceeds 50 GPa. The sliding friction properties were studied by ball-on-disc tests under different loads and speeds. The wear mode of the films was observed and analyzed. There exist spallation, abrasion and micro-ploughing wear modes under different loads. The critical load value was theoretically determined and tested to be 55 N. The results show that the alternating films have good wear resistance under heavy load and high speed.     

Micro-scale abrasive wear testing of PVD coatings on curved substrates

A method is presented which enables a micro-scale abrasion test to be used to measure the wear performance of a coating over a small region, typically of millimetre dimensions, on a curved surface. The method is also applicable to studies of the wear resistance of any bulk material with a surface having complex curvature. The technique is illustrated by measurement of the intrinsic abrasion resistance of thin PVD coatings of TiZrN, ZrNbN and TiNbN on both flat and cylindrical tool steel and flat stainless steel substrates. The ability to measure the wear resistance of both a coating and its substrate, independently of each other and by a single test, is confirmed by experiment.     

Wear resistance of coatings in high speed gear hobbing

Coating technology is one means of achieving a crucial enhancement in tool performance, especially in hobs that were among the first tools to be coated on a large scale. Nevertheless only few detailed analysis of wear mechanism have been done on field machines. The bifunctional coatings (combination of a tough, hard and refractory coating and of a self lubricating coating possessing a good thermochemical and abrasion resistance but a lower hardness) are very interesting since it is difficult to get a simple coating showing all these characteristics. The use of bilayer coatings raises several problems especially for dry and high speed cutting. Therefore, in order to investigate the behaviour of these bifunctional coatings, hobs have been coated by physical vapour deposition (PVD) methods. After the elaboration of a procedure for hobs testing, field tests have been performed. Results of tool life tests and investigations on tool wear mechanisms for different coated hobs are presented and discussed. The interesting performance in high speed gear hobbing of sintered high speed steel (HSS) hobs (ASP2052) combined with a (Ti,Al)N+MoS₂ coating is particularly underlined.     

Friction Reduction and Wear Resistance Enhancement of SiC and Si3N4 Ceramics under Dry Conditions

In this study, an effort was made to control the friction and wear behavior of silicon carbide (SiC) and silicon nitride (Si₃N₄) ceramics using an ultrasonic nanocrystalline surface modification (UNSM) technique. The friction and wear behavior of the ceramic specimens was investigated using a ball-on-disk tribotester under dry conditions against two different Si₃N₄ and bearing steel (SUJ2) balls. The experimental test results revealed the possibility of controlling the friction and wear behavior of ceramics, where the friction coefficient and wear resistance of the specimens were improved by the UNSM technique. The hardness of the specimens also increased after UNSM treatment, but it decreased abruptly with increasing depth from the very top surface. Microscratch tests showed that the critical load of the specimens was improved by the UNSM technique. In addition, Raman spectra results revealed that no additional phase was detected after UNSM treatment, but the intensity decreased after UNSM treatment. Hence, the UNSM technique ensures stronger ceramics and enables better friction and wear behavior than available conventional sintered ceramics.     

High temperature wear resistance of (TiAl)N PVD coating on untreated and gas nitrided AISI H13 steel with different heat treatments

The wear resistance of a PVD (Ti_0.7Al_0.3)N coating deposited on an as-received and gas nitrided AISI H13 has been examined by using ball-on-disc tests at room temperature and at 600 °C. In order to determine the influence of a previous heat treatment on this type of steel on the wear resistance of the (Ti_0.7Al_0.3)N coating, two commercial heat treatments were employed which gave rise to the same substrate hardness. Surface microhardness measurements have been carried out to determine the load-carrying capacity of the coated systems. In general, the wear behavior was found to be independent of the nature of the heat treatment applied to the substrate prior to the nitriding process but strongly dependent on the testing temperature. At room temperature, there were small variations between the different systems tested, whereas at high temperatures, clear differences were found between them. At 600 °C, a typical temperature that could be achieved during the aluminum extrusion processes, the nitrided H13 steel/(Ti_0.7Al_0.3)N PVD duplex coating shows a satisfactory wear resistance compared to both the nitrided steel and the steel substrate only coated with (Ti_0.6Al_0.4)N, which exhibited the worst performance. The satisfactory wear resistance observed for the duplex coating system at high temperature is mainly a consequence of two different aspects. Firstly, its higher load-carrying capacity due to the existence of a hard nitrided layer, as well as its high H/E ratio. Both parameters allow the presence of higher elastic strains without the failure of the ceramic layer, which would normally occur in the case of TiAlN PVD coatings deposited directly on the AISI H13 steel. Secondly, the intrinsic characteristics of the coating, i.e. its chemical constitution, which allows the formation of a dense oxide mixture inside the wear track that impedes both its further oxidation and the deterioration of the mechanical properties as consequence of nitrogen diffusion.     

镁合金防腐蚀表面处理研究进展

镁合金作为最轻的工程金属材料之一,它具有良好的比强度和比刚度、优良的阻尼减震性能、良好的铸造性能等特点,被誉为2l世纪绿色金属结构材料.但镁合金耐蚀性差,严重阻碍了它的工业应用,因此,镁合金的表面防护处理显得极为重要.综述了近年来镁合金防腐蚀表面处理的方法,主要有化学转化、阳极氧化、微弧氧化、金属镀(涂)层、有机涂层、物理气相沉积、离子注入、激光表面合金化等,并对镁合金表面处理的发展方向进行了展望.     

Improved Tribological Behavior of DLC Films Under Water Lubrication by Surface Texturing

Textured diamond-like carbon (DLC) films with the pattern of parallel grooves were developed by depositing DLC on textured stainless substrates in a PVD system. The texturing effects on tribological performance of DLC in water-lubricated condition were investigated. Results show that introducing specific patterns into DLC film not only retains the low friction coefficients, but also dramatically extends coating lifetime through affecting the coating delamination behavior and graphitization process during friction. Besides the adherence difference induced by surface texturing which could influence the delamination, another possible mechanism, “buffer stripes”, which is characteristic of the lateral soft/hard periodical structure, was proposed by us based on the Micro-Raman spectroscopy and nanoindentation analysis. Additionally, a much lower graphitization for textured DLC during friction may also be responsible for the improved wear resistance.     

Tribological evaluation of TiN and TiAlN coated PM-HSS gear cutter when machining 19MnCr5 steel

Two PVD coated powder metallurgy high speed steel (PM-HSS) gear cutters were investigated when machining helical gears made from AISI 19MnCr5 steel with hardness between 140 and 180 HV. Machining trials were carried out with gear cutters coated with TiAlN (nano layers) and TiN (mono layer). Crater and flank wears were measured and analysed after all the machining trials. Analyses of the worn tools show that the TiAlN coated gear cutter performed better than the TiN coated gear cutter. This can be attributed to its nano layers and the higher hardness of the TiAlN coating. The dominant tool wear mechanisms were adhesion, abrasion, delaminating of the coating layer and chipping of the cutting edge.     

A comparative study of the tribological behaviour of PVD coatings on the Ti-6Al-4V alloy

This work focuses on the tribological behaviour of PVD coated Ti-6Al-4V. Commercially available single layer CrN, CrN/NbN superlattice and multilayer WC/C coatings were taken into consideration. The dry sliding behaviour of the coated systems was studied by a flat-on-cylinder tribometer (load range 30–60 N). A critical load, corresponding to the end of coating life, was identified for each coated system. The highest critical loads were observed for CrN- and WC/C-coated Ti-6Al-4V. However, only WC/C also led to a significant decrease of the coefficient of friction. The good performance of WC/C-coated Ti-6Al-4V was ascribed to both the high H/E ratio of the coating and to the best match of elastic modulus with the substrate.