The effect of phosphating on the friction and wear properties of grey cast iron

The friction and wear resistance of two commercial manganese phosphate coatings have been evaluated. Grey cast iron wear pins were treated by the two processes and were tested by sliding against a steel disc, under both lubricated and dry sliding wear conditions.Phosphating increases the sliding distance to scuffing as well as the scuffing load, whilst marginally reducing the coefficient of friction. No advantage was found in phosphating dry sliding surfaces.Phosphating reduces the likelihood of adhesive wear in marginal or poorly lubricated sliding couples. The choice of phosphate coating is primarily dependent on the surface finish of the sliding counterface; thin coatings are suitable if the counterface is smooth but thicker coatings are superior against rougher surfaces.     

Preparation and characterization of spark-anodized Al-alloys: Physical, chemical and tribological properties

Aerospace applications and energy saving strategies in general boosted the interest and the research in the field of light weight materials, typically on alloys based on aluminium. Aluminium itself does not provide sufficient mechanical strength for structural parts, but there exists a lot of recently developed alloys containing silicon, copper, magnesium, zinc or manganese in various combinations and compositions exhibiting excellent mechanical properties. These alloys require surface treatments or coatings to withstand corrosive ambient conditions. Among those treatments known as chromate replacements, plasma oxidation processes were used for different applications, especially if the surfaces have to face mechanical load or severe environmental conditions. In this work, specimens of different aluminium alloys have been plasma oxidized by micro-arc treatment in silicate and phosphate solutions. The ceramic coatings were characterized with respect to phase composition, micro-hardness and corrosion stability. In addition, the tribological performance of the coatings was investigated using a ball-on-disc tribometer with reciprocating motion against sintered alumina ball. The typical worn surfaces of the Al substrate and the ceramic coatings were observed by a scanning electron microscope. Applying same wear conditions, the wear rates in different depth of the coatings are nearly similar. However, in a defined depth of the coatings, wear rate gradually decreases with wear duration. During friction process, a-stable transfer layer consisting of oxides was formed on the tribo-contact area of the coatings. The friction coefficient in a steady friction state is in the range of 0.8.     

Evaluation of unlubricated wear properties of plasma-sprayed nanostructured and conventional zirconia coatings by SRV tester

Atmospheric plasma spraying method was used to deposit nanostructured and conventional zirconia coatings using spray-dried nanostructured zirconia powder and conventional zirconia powder as feedstock, respectively. Their wear properties were evaluated comparatively by a sliding, reciprocating and vibrating (SRV) tester under dry conditions. The obtained results show that the wear properties of the plasma sprayed zirconia coatings deposited from spray-dried nanostructured zirconia powder were greatly improved compared with those of plasma sprayed zirconia coatings produced from conventional powder. The wear rates of nanostructured zirconia coatings are approximately half of those of conventional zirconia coatings. Under dry conditions, the wear mechanism for the plasma-sprayed nanostructured zirconia coatings is abrasive wear. Whilst in the case of plasma sprayed conventional zirconia coatings, it is a combination of abrasive wear and brittle fracture, the former is dominant wear mechanism. Their wear properties were explained in terms of their microstructure as well as mechanical properties and compared with the wear properties obtained under distilled-water lubricated conditions. Based on the experimental results, it is concluded that the finer debris is a critical factor for the improvement of wear properties of plasma-sprayed nanostructured zirconia coating under dry conditions. The wear properties of plasma sprayed zirconia coatings can be increased by the presence of water during the SRV testing.     

Residual stresses in aluminium phosphate sealed plasma sprayed oxide coatings and their effect on abrasive wear

Effect of residual stresses on plasma sprayed alumina and chromia coatings sealed with aluminium phosphate were studied as a function of the temperature of the sealing treatment. Stresses were measured by X-ray stress analysis and high-speed circular microhole drilling method. Residual stress states were correlated with other coating properties such as microhardness, porosity, microstructure and dry abrasion wear resistance. Correlations were found between sealing treatment temperature, residual stress state and wear resistance. Wear resistance of the oxide coatings was increased at all sealing temperatures. Sealing treatment affected coatings by two mechanisms. Aluminium phosphate sealing induced compressive stresses to coatings and simultaneously bonded coating lamellar structure.     

Wear Characteristics of Traditional Manganese Phosphate and Composite hBN Coatings

In this study, the tribological properties of traditional manganese phosphate coatings and composite hBN coatings

composed of nano-hexagonal boron nitride (hBN) in layered manganese phosphate crystals on AISI 1040 steel were investigated. Wear tests were carried out under controlled temperature and humidity using ball-on-disc tribometers for samples that were either submerged in oil or retaining oil on their surfaces at a sliding speed of 2.5 cm/s with loads of 1, 3, 5, and 10 N and sliding distances of 40, 80, 100, and 120 m. The surface profiles before and after the tests were used to characterize the wear. The surfaces of the coated samples were examined using scanning electron microscopy (SEM). The coefficients of friction and wear rates of the coated samples were also measured. The average wear rates of the composite hBN-coated samples were significantly lower than those of the traditional manganese phosphate–coated samples for each of the loading conditions for the oil submersion and retained oil tests. The coefficient of friction (COF) values for the traditional manganese phosphate–coated samples did not change significantly with increasing load. The COF values for the composite hBN coated–samples decreased with increasing load in the oil submersion test.     

Friction and wear measurements of laser-sintered and coated parts

The aim of this research is the investigation of surface properties, the measurements of friction coefficient and wear rate of laser-sintered and coated parts. The industrial background of this research is to prove applicability of laser-sintered prototype tools for injection moulding of fibre-reinforced polymers, furthermore to increase the wear resistance of unalloyed steel tools by laser coatings. The materials of the test specimens were laser-sintered phosphorous bronze and unalloyed steel. For increase of wear resistance we used hard Co-based and glassy-like Fe-based (FeB) coatings. As counter bodies we used polymers reinforced with short carbon and glass fibres. The laboratory model tests of selective laser-sintered parts were carried out on a pin-on-disk machine. In case of coated parts—with higher wear resistance—we used a cylinder-on-cylinder tribometer. The tribological properties were determined at different load and temperature conditions. The results of the investigation show that the friction coefficient and wear resistance of laser treated surfaces are good. The coefficient of friction of coated specimens is slightly less, but the wear rate is significantly less.     

Microstructure and properties of Fe–Al intermetallic coatings on the low carbon steel synthesized by mechanical alloying

Fe–Al coating was obtained on low carbon steel substrates using mechanical alloying and subsequent heat treatment. Light optical microscopy and a scanning electron microscope equipped with energy dispersive spectroscopy were used to conduct the microstructure characterization. Mechanical properties of the coatings were evaluated by microhardness measurements and wear tests. The corrosion behavior was determined by potentiodynamic polarization measurements in 3.5 % NaCl solution. The results of the mechanical and corrosion tests showed that the hardness and wear resistance of the coatings decreased with increasing the milling time, while increase in the milling time resulted in a significant increase in the thickness, porosity level, and corrosion resistance.     

Effects of anti-wear additives on friction and wear properties of Cr2O3 coating

The effects of some anti-wear additives on the friction and wear behaviour of plasma-sprayed Cr₂O₃ coating were investigated using a block-on-ring tester at ambient conditions. The results show that zinc dialkyldithiophosphate (ZDDP), tricesyl phosphate (TCP) and tributyl phosphate (TBP) significantly reduce the wear of Cr₂O₃ coating lubricated by paraffin oil. Additive concentrations as well as sliding time have great influence on the wear. The friction coefficient varies slightly with test conditions. The analysis by XPS of worn surfaces indicates that the wear resistance of these additives is due to the formation of tribochemical reaction films by reacting with Cr₂O₃ coatings.     

Wear resistance of nanocrystalline composite NI-B coatings

The nanocrystalline composite electrochemical coatings prepared with nickel matrix and boron particles were investigated. Nickel plating bath of low nickel ion concentration (0.76 mol/dm³) with brightening organic compound, surfactants and dispersed boron particles content was used for coatings electrodeposition. Boron particles content was determined gravimetrically. The dependence of boron content in composite Ni-B coatings on the concentration and kind of the organic additives was investigated. The coatings structure was established using TEM. The microhardness of the deposited layers was measured by Vickers' method at the load of 0.01 and 0.05 kg. The wear experiments of Ni-B coatings were made without lubrication using the technique based on measuring system comprising a flat surface and a ball. On the basis of measurements of wear traces diameter, the wear depth was calculated and assumed as a measure of wear resistance. Tribological properties were investigated using the disc-block measuring system. Friction tests were made on Amsler A-135 machine.The obtained results suggest that the organic compounds used in the experiments had a significant effect on the increase of boron content in coating and the development of nanostructure of nickel matrix.     

Functional behaviour of PVD coatings under sliding and rolling stress conditions

Whereas wear-resistant PVD coatings are well established in the field of metalcutting, and the functional and tribological behaviour of these coatings is well known under such conditions, PVD coatings are used only occasionally in mechanical engineering. The reason for this seems to be the lack of information concerning the functional behaviour of these coatings in closed tribosystems. To evaluate new areas of application together with optimised coating compounds, model wear tests were performed under sliding, rolling and slip-rolling stress conditions. In addition, the test parameters, such as sliding speed, load, ambient temperature, and number of revolutions were varied, as were the coating compounds and their thicknesses. The results obtained show that friction and wear of PVD coatings are both strongly influenced by the kind of stress and the test parameters themselves. Coatings that perform well under certain test conditions can break down quickly under some other stress conditions. TiN coatings, for example, which display low friction and wear under sliding friction, fail under rolling conditions very shortly afterwards.     

AlNiZr非晶纳米晶复合涂层的腐蚀磨损行为研究

为提高海洋极端环境下钢结构材料的耐腐蚀磨损性能,采用高速电弧喷涂技术制备了一种AlNiZr非晶纳米晶复合涂层,并研究了该涂层在质量分数为3.5%的NaCl溶液中的腐蚀磨损行为。结果发现,AlNiZr涂层组织较为均匀,致密性较好,相结构由非晶、纳米晶及晶化相共同组成,涂层非晶体积分数约为64.93%,平均显微硬度值为363HV0.1,与45钢基体之间的平均结合强度约为30.8 MPa;在干摩擦条件下其平均摩擦因数约为0.125,磨损体积约为0.134 mm3,磨痕宽度约为882.4 μm,磨损失效机制以氧化磨损和脆性剥层磨损为主,并伴有轻微磨粒磨损;在腐蚀介质条件下,由于受到腐蚀介质的润滑减摩作用,导致涂层的平均摩擦因数、磨损体积、磨痕宽度均有明显减小,其平均摩擦因数约为0.058,磨损体积约为0.02216 mm3,磨痕宽度约为314 μm,腐蚀磨损失效机制主要表现为剥层磨损形式,同时磨损起主导作用、腐蚀次之。与纯铝涂层相比,AlNiZr涂层表现出优异的耐腐蚀磨损性能。     

Unlubricated gross slip fretting wear of metallic plasma-sprayed coatings for Ti6Al4V surfaces

Plasma-sprayed Al–bronze or CuNiIn coatings are often applied to protect against fretting wear and extend the operational life of Ti-alloy compressor blades in turbine engines. In order to develop a fundamental understanding of how these coating systems perform under gross slip fretting conditions, bench level fretting wear tests were conducted at room temperature to simulate cold engine startup. Alternative coatings such as plasma-sprayed molybdenum and nickel were also evaluated because of their potential for reducing fretting wear under certain simulated engine conditions. The combination of scanning electron microscopy (SEM), surface profilometry, surface chemistry (EDS), and friction analysis were used to study coating performance and evaluate the interfacial wear mechanisms. In this study, it was determined that all coatings caused significant damage to the mating Ti6Al4V surfaces and that the wear mechanisms were all similar to those of the uncoated baseline case.     

Dry sliding friction and wear properties of metallic glass coating and martensite stainless coating

The wire arc spraying process was used to prepare FeB-based metallic glass coating and 3Cr13 coating. The effects of wear parameters, such as sliding distance, linear speed and normal loads, on the wear performances of the coatings were analyzed in detail. The results showed that, with increase in sliding distance, linear speed and normal loads, the volume losses of the metallic glass coatings increased. The relationships between wear behavior and microstructure of the coatings were discussed. The metallic glass coating had excellent wear resistance. The relatively wear resistance of the metallic glass coating was about 2.6 times that of the 3Cr13 coating under the same testing conditions. The main failure mechanism of the metallic glass coating was brittle failure and fracture.     

Study of abrasive wear phenomena in dry and slurry 3-body conditions

Machinery and equipment used in abrasive environments, such as the mining industry, suffer from severe wear. In order to understand wear and to prolong the life time of the machinery, it is important to understand how materials respond to wear depending on the environmental and tribological conditions imposed.This paper exposes a comparative study between the influence of two abrasive environments (dry and slurry) on hard particle coatings and steels. To study this, the 3-body wear behaviour was evaluated in a dry environment using a continuous abrasion test (CAT) and in a slurry environment using a slurry steel wheel abrasion test (SSWAT) method. Both tests are capable of experimentally modelling the high stress wear at 45 N and 216 N, using quartz sand as an abrasive. The tests were performed on two types of coatings processed by sintering and hardfacing and martensitic steel was used as a reference. The wear was indicated as volume loss by measuring the samples before and after the tests. Furthermore, the specific wear energy was calculated in order to have a fundamental understanding about the material's response to wear. A correlation between the wear rate and the particle brakeage index (PBI) was done for the dry conditions using different loads, in order to explain the interdependence between the two parameters and the change in the wear mechanism between the two loads. The influence of load on the wear of the materials showed different wear mechanisms on coatings compared to the steel in the same environmental conditions. However, a change in wear mechanism at different load levels was observed, which might be directly dependent on the change of the particle's motion from sliding to rolling combined with the change in their shape and size. The results showed that the need to study the influence of different abrasive conditions on the material wear is crucial in order to improve the lifetime and the cost efficiency of the machinery used in such environments. The hard-particle coatings showed comparatively low wear rates promising a great potential in improving the lifetime of industrial equipments in different environments.     

磷酸锰转化涂层和硫化亚铁涂层的摩擦学性能对比

为了在重载蜗杆传动中以钢蜗轮替代青铜蜗轮,在20Cr钢表面分别制备了超微细磷酸锰转化涂层和硫化亚铁涂层,在摩擦磨损试验机上对两种涂层的摩擦学性能进行了对比;用SEM和EDX分析了涂层表面、磨损面的形貌与成分,采用XRD分析了涂层的相结构。结果表明:在载荷低于300 N时,两种涂层均具有良好的减摩耐磨性能;当载荷大于500 N时,硫化亚铁涂层的减摩耐磨效果不明显,而超微细磷酸锰转化涂层具有持续的减摩耐磨特性。     

Deposition of duplex Al2O3/TiN coatings on aluminum alloys for tribological applications using a combined microplasma oxidation (MPO) and arc ion plating (AIP)

Microplasma oxidation (MPO) has recently been studied as a cost-effective plasma electrolytic process to provide thick and hard ceramic coatings with excellent surface load-bearing capacity on aluminum alloys. However, for sliding wear applications, such ceramic coatings often exhibit relatively high friction coefficients against many counterface materials. Although coatings deposited by physical vapour deposition (PVD) techniques such as TiN coatings are well known for providing surfaces with a high hardness, in practice they often exhibit poor performance under mechanical loading, since the coatings are usually too thin to protect the substrate from the contact conditions. In this paper, these challenges were overcome by a duplex process of microplasma oxidation and arc ion plating (AIP), in which an alumina layer Al₂O₃ was deposited on an Al alloy substrate (using MPO as a pre-treatment process) for load support, and a TiN hard coatings were deposited (using AIP) on top of the Al₂O₃ layer for low friction coefficient. Microhardness measurements, pin-on-disc sliding wear tests, and antiwear tests using a Timken tester were performed to evaluate the mechanical and tribological properties. Scanning electron microscopy (SEM) was used to observe coating morphology, and to examine wear scars from pin-on-disc test. The research demonstrates that a hard and uniform TiN coating, with good adhesion and a low coefficient of friction, can successfully be deposited on top of an alumina intermediate layer to provide excellent load support. The investigations indicate that a duplex combination of MPO coating and TiN PVD coating represents a promising technique for surface modification of Al alloys for heavy surface load bearing application.     

Fretting of WC/a-C:H and Cr2N Coatings Under Grease-Lubricated and Unlubricated Conditions

The fretting phenomenon was investigated experimentally in contacts between coated and uncoated steel rod and ball specimens generating a circular Hertzian contact. A fretting wear test rig equipped with a video camera was used to observe the effects of fretting on coated steel surfaces in both grease-lubricated and unlubricated environments. Tungsten carbide reinforced amorphous hydrocarbon (WC/a-C:H) and chromium nitride (Cr₂N) coatings were tested and compared. Fretting wear volumes and surface profiles are presented for both grease-lubricated and unlubricated conditions. Videos of a coated ball fretting against a transparent sapphire flat were recorded and screen captures are presented. The role of normal load, lubrication, frequency, and amplitude of motion on the fretting wear of coatings is discussed. The lubricant released from the grease was observed to flow through channels in the stick zone of the fretting contacts. Both coatings were found to reduce fretting wear. WC/a-C:H was more effective at reducing wear under unlubricated conditions. WC/a-C:H decreased fretting wear more than Cr₂N when delamination was avoided in grease-lubricated contacts.     

Improved mixed and boundary lubrication with glycerol-diamond technology

Abstract

The fuel economy and reduction of harmful elements in lubricants are becoming important issues in the automotive industry. An approach to respond to these requirements is the potential use of low friction coatings in engine components exposed to boundary lubrication conditions. Diamond-like carbon (DLC) coatings extensively studied as ultralow friction films to protect the surfaces of ductile metals for space applications are expected to fulfil this part. The main purpose of this work is to investigate the friction and wear properties of glycerol lubricated DLC coatings under boundary lubrication conditions. The DLC material consists of tetrahedral hydrogen free amorphous diamond-like carbon (denoted as ta-C) as shown by the time of flight secondary ion mass spectroscopy (ToF-SIMS) analyses and the nanoindentation measurements. The friction coefficient below 0&middot.01, called superlubricity, and no measurable wear were obtained by sliding the ta-C/ta-C friction pair in the presence of pure glycerol as a lubricant at 353 K. The mechanism by which glycerol is able to reduce the friction in the millirange was revealed by ToF SIMS analyses inside and outside wear scars formed by friction experiments using deuterated glycerol and ¹³C glycerol.     

Two-body free-abrasive wear of polyethylene, nylon1010, expoxy and polyurethane coatings

Two-body free-abrasive wear behavior of polyethylene (PE) coatings, nylon1010 (PA1010) coatings, polyurethane (PU) coatings, and expoxy (EP) coatings was investigated. Abrasive wear tests were performed on a turnplate abrasive wear test machine JMM. Hardened and low-temperature tempered steel 45 was used as a reference material. The results shown that in abrasive wear resistance, the PU coatings are approximately 120%, about 5 times larger than the PE coatings and 3 times larger than the PA1010 coatings and the EP coatings, the EP coatings and the PA1010 coatings approach to 40%, and the PE coatings about 20% compared with the reference material (steel 45). Of all the tested polymer coatings, the PU coatings are the best, the PE coatings the worst, and the PA1010 coatings and the EP coatings intermediate. Wear morphologies of the polymer coatings were observed by scanning electron microscope (SEM). Main wear mechanisms of the tested polymer coatings include ploughing wear for the PE coatings and the PA1010 coatings, fatigue wear for the PU coatings and fatigue fracture as well as some brittle fracture and somewhat ploughing wear for the EP coatings.     

TiSiC,TiSiC-Zr,and TiSiC-Cr Coatings—Corrosion Resistance and Tribological Performance in Saline Solution

TiSiC coatings alloyed with Zr and Cr were deposited on Si and 316 L steel substrates by a cathodic arc method in a CH₄ reactive atmosphere. The corrosion and wear behavior of the coatings in 0.9% NaCl solution was investigated. Corrosion resistance of the coatings was evaluated by electrochemical tests. The electrochemical polarization measurements were conducted at room temperature in the potential range ?1 and 1.5 V, with a 0.167 mVs^?1 scan rate. Compared to the uncoated 316 L substrates, the coated ones showed nobler characteristics, with more electropositive corrosion potentials, lower corrosion current densities, and higher polarization resistances. TiSiC-Zr exhibited the lowest corrosion current density (0.62 μAcm^?2) and the highest protection efficiency (69.5%). The tribological performance of the coatings under corrosive conditions (0.9% NaCl solution) was investigated using a ball-on-disc tribometer (6-mm-diameter sapphire ball, 5 N load, 0.15 ms^?1 sliding speed, 400 m sliding distance). The TiSiC-Cr coating demonstrated the best wear behavior, with a wear rate of 3.2 × 10^?6 mm³N^?1m^?1, followed by TiSiC and TiSiC-Zr. The morphologies and compositions of the worn surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) in order to identify the wear mechanism. Corrosion, debris adhesion, and oxidation were found to be the dominant wear processes.