Tribological properties of combined molybdenum coatings formed by electric-spark alloying on stainless steel

To improve the operational properties of the parts of machines made of quenched stainless steel 30X13, the surface were hardened by electric-spark alloying (ESA) with combined coatings (molybdenum + chromium and molybdenum + bronze). The results of investigations showed the correlation between the wear resistance of coatings and their hardness. It has been noted that the roughness of all alloyed coatings after tribological tests lowered, while the roughness of unalloyed surface of steel 30X13 increased. The smallest coefficient of friction has been established for samples alloyed with the molybdenum + bronze combined coating.     

Tribological properties of electrospark-deposited and further laser-hardened coatings

The tribological properties of the coatings based on fine-grained VK6-M hard alloy, chromium, and molybdenum have been investigated. The coatings were obtained by the electrospark deposition followed by the laser treatment. The electric spark deposition does not affect the coefficient of friction and temperature in the friction zone of the coated surface in contrast to steel 45 surface. Additional laser treatment reduces the dispersion of the friction coefficients and temperatures, but hardly alters their level. The wear rate of the coatings increases in the direction VK6-M → Cr → Mo → steel 45. A hard alloy coating is most effective, since the wear rate decreases as much as 15 times compared to steel 45. The wear rate of the coatings based on chromium and molybdenum is 1.7 and 1.4 times lower than that of steel 45. The laser treatment reduces the wear rate even more, i.e., by 70% for the coating based on the hard alloy and 3.5 and 3 times, respectively, for coatings based on chromium and molybdenum.     

Tribological characterization of thin hard coatings by reciprocating sliding tests

Thin hard coatings on metal or ceramic surfaces offer a large spectrum of improvements of the friction and/or wear behaviour of tribosystems. The development of coatings and the tailoring of their properties require test methods providing information about their friction and wear behaviour. A new wear test standard (ASTM) is under development for the evaluation of friction and wear quantities for sliding motions using the reciprocating sliding mode. The applicability of this test method to coated specimens was checked by testing uncoated and coated steel specimens in contact with alumina balls, whereby lower loads were used than in the ASTM proposal for bulk materials. Additionally, the influence of the relative humidity of the surrounding air at room temperature on friction and wear results was examined.     

Friction and wear behaviors of MoS2/Zr coated HSS in sliding wear and in drilling processes

MoS2 metal composite coatings have been successful used in dry turning, but its suitability for dry drilling has not been yet established. Therefore, it is necessary to study the friction and wear behaviors of MoS2/Zr coated HSS in sliding wear and in drilling processes. In the present study, MoS2/Zr composite coatings are deposited on the surface of W6Mo5Cr4V2 high speed steel(HSS). Microstructural and fundamental properties of these coatings are examined. Ball-on-disc sliding wear tests on the coated discs are carried out, and the drilling performance of the coated drills is tested. Test results show that the MoS2/Zr composite coatings exhibit decreases friction coefficient to that of the uncoated HSS in sliding wear tests. Energy dispersive X-ray(EDX) analysis on the wear surface indicates that there is a transfer layer formed on the counterpart ball during sliding wear processes, which contributes to the decreasing of the friction coefficient between the sliding couple. Drilling tests indicate that the MoS2/Zr coated drills show better cutting performance compared to the uncoated HSS drills, coating delamination and abrasive are found to be the main flank and rake wear mode of the coated drills. The proposed research founds the base of the application of MoS2 metal composite coatings on dry drilling.     

Tribological characteristics of hardened-and-tempered structural steels turned by inserts covered with multicomponent PVD coatings

The effect of coatings deposited on cutting tools using the PVD method on the tribological characteristics of the surface layer after the finish turning of 41Cr4 and 30CrMnSi steels is considered. The tribological characteristics of the turned surfaces change substantially. The best results are achieved when using the (AlTi)N coating, which ensures substantial decreases in the coefficient of friction (by 35–40%) and the temperature in the friction zone (by up to 30%). The dependences of the wear on the friction path are linear; the wear rate of the surfaces turned by the coated tools is significantly lower than that for the surfaces turned by the uncoated tools. Compared to the uncoated R25 hard alloy, the difference in the wear rates reaches 60% in favor of (AlTi)N and (TiAl)N coatings. A decrease in the thickness of the coating from 4 to 2 μm leads to a growth in the coefficient of friction and the temperature. An X-ray structural analysis of the surface layers of the turned specimens has revealed the presence of Fe-Al solid phases, which improve the wear resistance of the surface and the efficiency of coatings like (AlTi)N.     

Tribological Properties of DLC Coatings in Helium

The aim of this research work was to investigate tribological properties of low-friction DLC coatings when operating in helium atmosphere. Two commercial DLC coatings (a-C:H and Me-C:H) were included in the investigation and compared to reference PTFE-based coatings, normally used on components operating in helium. Coatings were deposited on hardened 100Cr6 bearing steel discs and tested against uncoated steel balls in low-load pin-on-disc contact configuration. Investigation was focused on the effect of substrate roughness (R _a ?=?0.05?C0.2???m) and contact conditions, including contact pressure (150?C350?MPa) and sliding speed (0.2?C0.4?m/s) on the coefficient of friction of DLC coatings operating in helium. Results of this investigation show that for low-load sliding contact DLC coatings provide low friction in helium atmosphere, similar to soft PTFE-based coatings. At the same time DLC coatings investigated were found to substantially reduce wear of the coated surface. However, while the wear of the coated part has been more or less eliminated, application of DLC coating prolongs running-in and increases wear of the steel counter-part. Furthermore, also in helium atmosphere tribolgical behaviour of DLC coatings showed dependence on the coating type and contact conditions.     

Wear resistance and anti-sticking properties of duplex treated forming tool steel

The aim of this work was to investigate the potential of using hard physical vapour deposition (PVD) coatings on forming tools, as well as to determine the influence of plasma nitriding on the load-carrying capacity and wear resistance of coated tool surfaces. A load-scanning test rig was used for evaluation, where duplex treated cold work tool steel samples were loaded against soft austenitic stainless steel and hardened ball bearing steel, respectively. Four different coatings (TiN, TiB₂, TaC and DLC) and two substrate treatments (hardening and plasma nitriding in two different gas mixtures) were included.Plasma nitriding alone significantly improved the friction, wear, and anti-sticking properties of the tool steel. PVD coating, and especially PVD coating of nitrided tool steel further improved the performance. Therefore, from the point of view of tool life as well as work peace surface quality, the DLC coating with its excellent anti-sticking properties and sufficiently good wear resistance represent the best solution for forming tool applications of austenitic stainless steel.     

On dry sliding friction and wear behaviour of PEEK and PEEK/SiC-composite coatings

In this work, polyetheretherketone (PEEK) and PEEK/SiC-composite coatings were deposited on Al substrates using a printing technique to improve their surfaces performance. The objective of this work was to investigate coatings friction and wear behaviour. Especially, the effect of sliding velocity and applied load on coatings friction coefficient and wear rate was evaluated in range of 0.2-1.4 m/s and 1-9 N, respectively. Compared to Al substrate, the coated samples exhibit excellent friction coefficient and wear rate. For PEEK coating, under an applied load of 1 N, the increase in sliding velocity can result in decreasing of friction coefficient at a cost of wear resistance. Under a load of 9 N, however, PEEK coating exhibits the highest friction coefficient and wear rate at an intermediate velocity. These influences appear to be mainly ascribed to the influence of contact temperature of the two relative sliding parts. In most test conditions, the composite coating exhibits better wear resistance and a little higher friction coefficient. SiC reinforcement in composite coating plays a combined role. First of all, it might lead to energy dissipation for activation of fracture occurred on the interface of PEEK and the powders. Moreover, it can reduce coating ploughs and the adhesion between the two relative sliding parts.     

Dry friction and wear characteristics of nickel/carbon nanotube electroless composite deposits

Ni/carbon nanotube (Ni/CNTs) composite coatings were deposited on carbon steel plate by electroless deposition. The friction and wear properties were examined under dry sliding conditions using the ball-on-disk configuration. For reference, carbon steel plate was coated with Ni, Ni/SiC and Ni/graphite. The results show that the Ni/CNT coating has a microhardness value of 865 Hv, greater than for SiC reinforced composite deposits. The Ni/CNTs composite coating possesses not only a higher wear resistance but also a lower friction coefficient, resulting from their improved mechanical characteristics and the unique topological structure of the hollow nanotubes.     

Performance of PVD (Zr,Ti)N-coated cemented carbide inserts in cutting processes

(Zr,Ti)N coatings with two different gradient structures were deposited on YT15-cemented carbide inserts by multi arc ion plating. Microstructure and properties of these coatings were examined. Dry cutting tests of these coated inserts against 40Cr hardened steel are carried out. This paper presented a detailed analysis of the cutting performance and wear mechanism of these coated inserts. The critical load of EGC shows a little increase compared with TGC because of the thermal expansion coefficient gradient. Compared with YT15 tool, (Zr,Ti)N-coated tools lead to a high quality and good consistency of machined surface during the whole machining process; the cutting temperature will also decrease, but the cutting force change a little. The abrasive wear and boundary wear are the main mode of flank wear, and crater wear and adhesive wear are the main rake wear modes during the machining of 40Cr hardened steel. The (Zr,Ti)N coatings effectively improve the wear resistance of the tools especially the crater wear. The thermal expansion coefficient gradient structure of EGC will reduce the thermal damage of the coating, and its multi-layer structure will mitigate and block the initiation and propagation of microcracks.     

Nd:YAG laser alloying of high-speed steel tools with BN and Ti/BN and the effects on turning performance

A 400 W pulsed Nd:YAG laser was used to surface alloy BN and Ti/BN on AISI M2 steel using hexagonal BN powder and Ti foil (25 μm thickness). The clearance (flank) faces of the single-point tool were laser alloyed using BN and Ti/BN. Optical metallography, scanning electron microscope, Vicker's microhardness and X-ray diffraction were employed to characterize the alloyed layers. The depths of the laser-alloyed zones of BN- and Ti/BN-alloyed tools were about 140 μm and 260 μm respectively. The hardness of the laser-alloyed layer with BN was about 640 HV while that of the alloyed layer with Ti/BN was about 680 HV. The alloyed layers were free from cracks and porosity. Both the alloyed and unalloyed tools were then tested on a 14.7 kW engine lathe to turn AISI 1045 steel workpieces. The results indicated that the tool life of BN-alloyed tools was about 200% higher than that of the unalloyed tools, while the tool life of Ti/BN-alloyed tools was about 260% higher when the tool life criterion was chosen as 0.3 mm flank wear. Also, the tool wear rate was reduced by about 30% and 50% for BN-and Ti/BN-alloyed tools, respectively. The reduction in tool wear of the alloyed tools was attributed to a reduction of the chip-tool contact length (and consequently the reduction of coefficient of friction between the tool and workpiece material) and to the different chip formation mechanisms.     

Wear and friction characteristics of atmospheric plasma sprayed Cr3C2–NiCr coatings

ABSTRACT

The present work focuses on investigating the wear and friction characteristics of the Atmospheric Plasma Sprayed Cr₃C₂-NiCr coatings deposited onto the surface of die steel material. The as-sprayed specimens were characterized. The coating porosity, bond strength and microhardness values were evaluated. Wear tests were performed on the high-temperature pin-on-disc tribometer at room temperatures, 400°C and 800°C under two loads as 25N and 50N in the laboratory. The wear mechanisms of all the worn-out samples were studied by scanning electron microscopy (SEM) technique. The specific wear rates and the coefficient of friction values were analyzed. The developed coating showed better wear resistance than its uncoated counterpart. The coefficient of friction values for coated specimens decreased at elevated temperatures. At room temperatures, the wear mode was observed to be adhesive and further at elevated temperatures of testing, the wear mode was observed to be the combination of oxidative, adhesive and abrasive.     

Tribotechnical properties of thin-film coatings obtained by the tribomodifcation of crankshaft pins for ship diesel engines

The tribotechnical properties of thin-film coatings obtained as a result of the tribomodification of 40Kh steel by various organic-inorganic tribotechnical materials (natural inorganic and synthetic polymers), as well as the compositions and composites created based on vermiculite are considered in the work. Comparative tribotechnical tests have made it possible to establish that the most promising materials for the tribomodification of the friction surfaces of steels are nanostructured composites based on vermiculite, which make it possible to get the minimum coefficient of friction and high wear resistance of the conjugation under the friction condition at boundary lubrication.     

表面处理复合涂层的摩擦学评价方法

从涂层的摩擦学评价的重要参数、涂层与基体间的粘合力、涂层力学性能、涂层的摩擦学特性以及涂层零件的摩擦学特性等方面介绍了金属切削刀具和模具等工件的复合涂层的摩擦学涂层的评价方法,指出了在轻合金涂层材料、低摩擦因数的涂层、涂层韧性的改进、涂层磨损试验方法、涂层设计和评价的工具等方面需要进一步研究。     

Friction and wear behaviour of rapid prototype parts by direct metal laser sintering

Abstract

Rapid prototyping and manufacturing (RP/M) is one of the proven tools for product development owing to its advantages such as short product cycle, high quality product and possibility of fabricating functionally gradient materials. Several RP/M techniques do exist. Among them, direct metal laser sintering (DMLS) method is quite popular as near net shape components with high dimensional accuracies can be manufactured. Meager information is available as regards the tribological behaviour of laser built parts, although this is vital in judging the suitability of built-up parts for applications where sliding is inevitable. In the light of the above, the present investigation is aimed at building parts by DMLS technique of RP/M using 50 μm iron powder and characterising its density, microstructure, microhardness, tensile strength, friction and wear behaviour under sliding conditions. The effect of laser speed on the above properties of built-up parts has been studied. The build layer thickness was maintained at 50 μm. Laser diameter of 0˙4 mm, laser power of 180 W and hatch spacing of 0˙2 mm were adopted. However, the laser speed was varied from 50 to 125 mm s^–1 in steps of 25 mm s^–1. Laser speed had a profound influence on density, microstructure, microhardness, tensile strength, friction and wear behaviour of built-up parts. Lesser laser speed resulted in higher density, microhardness, tensile strength and wear resistance while higher laser speed promoted lowering of coefficient of friction.     

Recovery of the efficiency of shaft-insert friction pair of plain bearings via laser cladding

The paper presents results of metallographic and tribological tests of steel 38X3MA samples coated by nickel-based powder materials using a fiber laser. Microhardness, wear rate, scoring resistance, and antifriction behavior of B83 babbit-surfaced layers were found. The developed technology of laser cladding may be used to recover the worn friction surfaces and increase the reliability and durability of new parts in operation.     

Friction and wear of nitride and carbide coatings in contact with aluminum

The study of the physical and mechanical properties of multicomponent nitride ((AlSi, Ti)N and (AlSi,Cr)N), carbides ((AlSi, Ti)-C:H and (AlSi,Cr)-C:H) coatings deposited on the surface substrate from 40Kh steel has been carried out to determine the impact of the load and the sliding velocity on the coefficient of friction. The empirical model of the coefficient of friction of the coating-aluminum couples has been proposed in order to find the nature of the friction wear of coatings. A comparative evaluation of the wear resistance of the coatings at normal and elevated temperatures has been conducted.     

Behaviour of MoDTC in DLC/DLC and DLC/steel contacts

Diamond-like carbon (DLC) coatings are beginning to be used on machine components parts because of their excellent friction and wear resistance properties. It is hence important to be able to formulate lubricants able to work effectively with these coatings. This requires knowledge of how the various surface-reactive additives generally employed in lubricants behave with DLCs. This paper compares the behaviour of seven types of DLC, a-C, a-C:H, a-C:H:W, a-C:H:WC, Si-DLC, ta-C, ta-C:H, lubricated with molybdenum dialkyldithiocarbamate (MoDTC) solution. It is found that a-C and a-C:H:WC give lower boundary friction than the other types of DLC. MoDTC improves the wear resistance of DLC/DLC contacts but appears to greatly degrade the wear resistance properties of some DLCs in DLC/steel contacts, even though Mo-derived tribofilms form on all DLCs.     

Structure and wear resistance of electron-beam nitrous coatings

The paper deals with the study of the tribological properties of nitrogen-containing austenite coatings deposited by electron-beam facing during abrasive wear and the sliding friction of a VK6 hard alloy indentor. The abrasive wear resistance of the nitrous coatings deposited by the electron-beam facing of steel 60Kh24AG16 powder in quartz sand is lower than that of the steel 65G coatings after hardening; it increases with increasing mass share of the filler. At contents of nitrided ferrovanadium of 10?C30 wt % the abrasive wear rate increases by 30?C50%, respectively. It is found that under a certain load applied to the VK6 ball indentor the friction coefficient and the shear resistance of the surface layer diminish. It is shown that under heavy specific loads applied to the ball indentor the nitrous coating faced from steel 60Kh24AG16 powder and composite nitrous coatings have wear resistance exceeding that of steels 110G13 and Kh18N10 by more than two and seven times, respectively. Based on the results of structural studies an explanation of the observed behavior of the nitrous coatings is proposed.     

Friction and Wear Behavior of WS2/Zr Self-lubricating Soft Coatings in Dry Sliding Against 40Cr-Hardened Steel Balls

WS₂ and WS₂/Zr self-lubricating soft coatings were produced by medium-frequency magnetron sputtering, multi-arc ion plating and ion-beam-assisted deposition technique on the cemented carbide YT15 (WC + 15 % TiC + 6 % Co) substrates. Microstructural and fundamental properties of these coatings were examined. Sliding wear tests against 40Cr-hardened steel using a ball-on-disk tribometer method were carried out with these coated materials. The friction coefficient and wear rates were measured with various applied loads and sliding speeds. The wear surface features of the coatings were examined using SEM. The results showed that the WS-1 specimen (with WS₂/Zr composite coating) has higher hardness and coating/substrate critical load compared with that of the WS-2 specimen (only with WS₂ coating). The friction coefficient of WS-1 specimen increases with the increase in applied load and is quite insensitive to the sliding speed. The wear rate of the WS-1 specimen is almost constant under different applied loads and sliding speeds. The WS-1 specimen shows the smallest friction coefficient and wear rate among all the specimens tested under the same conditions. The WS-1 specimen exhibits improved friction behavior to that of the WS-2 specimen, and the antiwear lifetime of the WS₂ coatings can be prolonged through adding Zr additives. The self-lubricating and wear mechanism of the WS₂/Zr coating was also found from the sliding wear tests.