Tribological Behavior of New Martensitic Stainless Steels Using Scratch and Dry Wear Test

This paper focuses on the tribological characterization of new martensitic stainless steels by two different tribological methods (scratch and dry wear tests) and their comparison to the austenitic standard stainless steel AISI 316L. The scratch test allows obtaining critical loads, scratch friction coefficients, scratch hardness and specific scratch wear rate, and the dry wear test to quantify wear volumes. The damage has been studied by ex situ scanning electron microscopy. Wear resistance was related to the hardness and the microstructure of the studied materials, where martensitic stainless steels exhibit higher scratch wear resistance than the austenitic one, but higher hardness of the martensitic alloys did not give better scratch resistance when comparing with themselves. It has been proved it is possible to evaluate the scratch wear resistance of bulk stainless steels using scratch test. The austenitic material presented lower wear volume than the martensitic ones after the dry wear test due to phase transformation and the hardening during sliding.     

The relationship between the abrasive wear resistance,hardness and microstructure of ferritic materials

The relationship between the abrasive wear resistance and bulk hardness of ferritic materials in the pearlitic and martensitic conditions has been investigated. For pearlitic materials the abrasive wear resistance and bulk hardness are dependent on the pearlite content and for martensitic materials the abrasive wear resistance and bulk hardness are dependent on the square root of the carbon content. Thus for each structure there is a linear relationship between abrasive wear resistance and bulk hardness, but it is suggested that the material microstructure has a greater influence on wear resistance than the bulk hardness.     

A contribution to the surface analysis and characterisation of HVOF coatings for petrochemical application

The appropriate selection of bulk materials and coatings of valve components is an important factor for the economic success of oil and gas production activities in the petrochemical field. Materials and coatings are important because particle erosion and surface wear are associated to corrosion by hydrogen sulphide during oil and gas flow. The wear of high pressure valves of gas system will lead to pollution, safety problems and cost increases. The most common solution of these problems is the deposition of hard materials as tungsten carbide or chromium carbide by thermal spray. These coatings are deposited by high velocity oxygen fuel (HVOF) thermal spray process to obtain a very high hardness with excellent cohesion and adhesion. Tungsten carbide cobalt–chromium based coating, chromium carbide nickel–chromium coating as well as Inconel 625 have been adopted in the specifications of petrochemical companies and their behaviour and wear, erosion and corrosion properties are reported in the literature.

This paper addresses the experimental study, surface analysis and functional characterisation of HVOF coatings innovative for the specific application such as NiAl and composite material WC/intermetallic compounds containing Ni, Cr, Co and Mo. These coatings have been systematically submitted to corrosion and functional tests based on the determination of the behaviour of the coatings in H₂S and CO₂ atmosphere and to wear and erosion according to standard ASTM G75-95 (slurry test); material loss and surface damage have been determined; the coatings have been completely characterised from the point of view of the structure (morphology, porosity, hardness, wear) and of the surface properties by means of a prototype 3-dimensional (3-D) stylus micro-geometrical surface analysis system; their corrosion and functional behaviour have been compared with the behaviour of the above mentioned coatings.

The slurry test allows a clear discrimination among the performances of analysed coatings. Namely, WC/Mo compound, because of its carbide content, shows fairly good behaviour in an erosive environment and higher erosion resistance than Inconel 625 and NiAl; all the tested coatings show similar behaviour in a corrosive environment.     

Ball-cratering abrasion tests of high-Cr white cast irons

The application of a ball-cratering method to test three-body abrasive wear of bulk materials in the presence of large abrasive particles has been investigated. Three high-Cr white cast irons (WCIs) with different material properties were used as wear samples. Abrasive slurries contained two types of abrasive particles, silica sand and crushed quartz. Silica sand and crushed quartz particles have similar chemical composition and hardness but differ in sharpness. Wear rates of WCI samples were determined and the worn surfaces were examined by optical microscopy, SEM and Talysurf profilometry.It was found that the ball-cratering test can differentiate between the wear resistances of materials with similar properties. The wear resistance of WCIs in the presence of silica sand increased with increasing the hardness of the wear sample and decreasing the size of carbides in the microstructure. Smaller silica sand particles caused less wear damage than larger silica sand particles, even though the smaller particles were slightly sharper than the larger ones. When silica sand and quartz particles of the same size were used, the angular quartz particles caused much higher wear than the rounded silica sand particles. Surface morphologies of the wear craters on the WCI samples were examined in an SEM and then compared with the morphologies of the worn surfaces from slurry pumps. It was found that the silica sand particles generated surface morphologies similar to those found in the worn slurry pumps. In these surfaces the matrix was preferentially worn out and hard carbides were protruding. Wear surface morphologies produced by the angular quartz particles were different. They consisted of numerous superimposed indents and the microstructure phases were not distinguishable. This indicates that the type of abrasive particles used in ball-cratering testing significantly affects the test outcomes in terms of wear rates and wear surface morphology.     

Investigation of abrasive wear resistance and wear mechanism of composite alloys

The abrasive wear resistance of composite alloys comprising hard tungsten carbide and soft CuNiMn matrix under different wear conditions has been investigated and compared with CrMo cast iron. It was found that Yz-composite alloy with hard cast angular tungsten carbide has greater wear resistance than CrMo cast iron under two-body wear conditions, but lower resistance than Cr-Mo cast iron under three-body wear conditions. It was found that under three-body wear conditions selective wear of the matrix and digging or fragmentation of tungsten carbide particles dominate in Yz-composite alloy, and microcutting and deformed ploughing is dominant under two-body wear conditions. The abrasive wear resistance of composite alloys under two-body wear condition is independent of bulk hardness, but is closely related to the microhardness of tungsten carbide.     

General aspects for tribological applications of hard particle coatings

Hard coatings, consisting of WC, TiC or Cr₃C₂ particles with a nickel or cobalt matrix were compared with conventional wear-resistant materials like hardened steel 100 Cr6, Ferro TiC P143, WC-Co hard metal and a widely used thermal spray layer NiCrBSi. The coating procedure was flame spraying and diffusion welding. Some layers were remelted using an electron beam to improve their microstructural properties, porosity and binding to the bulk material.

Wear tests were performed under different degrees of severity to qualify the resistance of the coating, using abrasive, sliding and impact test methods representing different wear mechanisms. It is shown that the benefit of the hard particle content depends on the acting loading situation. Under abrasive and sliding conditions the advantage of a high hardness level, i.e. a high concentration of hard phases, could be demonstrated. For impact loading, causing severe surface fatigue, homogeneous materials with high toughness, such as martensitic steels, are beneficial; followed by coatings with a high concentration of ductile matrix. In some cases, the weaknesses, such as brittleness and limited strength of binding to the bulk, could be improved by electron beam remelting.     

Surface Hardness and Abrasive Wear Resistance of Ion-Implanted Steels

The hardnesses of nitrogen-implanted steel surfaces have been measured with an abrasive wear technique capable of characterizing surface layers as thin as 25 nm. Treated steel disks and reference disks were abraded with 1–5 μm diamond, and relative wear resistances were calculated from the mass losses. Surface hardness was obtained from a relationship between wear resistance and hardness.

The surface of a hardened and tempered carbon steel implanted with nitrogen ions (10¹⁷/cm²) was significantly harder than with other treatments including quench hardening and nitriding. The hardness decreased to the bulk value over a depth corresponding to the initial implantation depth.

Nitorgen-implanted stainless-steel surfaces wore faster than un-implanted ones, possibly due to interference with transformation hardening which normally occurs during wearing. This “softening” effect persisted to depths several times the depth of implantation, and may help to explain the reduction of sliding wear produced by the implantation of stainless steels. Analyses by Auger electron spectroscopy indicated nitrogen migrated toward the bulk during wear.

Titanium implanted in stainless steel (4.6 × 10¹⁷ ions/cm²) produced a very hard surface with more than 10 times the abrasive wear resistance of the bulk metal.     

Wear by hard particles

Abrasive wear can be caused by hard particles sliding on a softer solid surface and displaying or detaching material. Different types of interactions are distinguished between the sliding particles and the wearing surface of the solid. Frequently, resistance against abrasive wear is only considered as a function of hardness of the wearing material. However, a more general model shows that, depending on the interaction, the capability of deformation or the fracture toughness of the wearing material is very important in addition to hardness. Abrasive wear resistance can substantially be improved by second phases embedded in a hard or soft matrix. The theoretical models are supported by a lot of experimental results from studies on metallic or ceramic materials.     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

Subsurface characteristics of an abraded low carbon steel

Ductile metals commonly exhibit plastic deformation at and near the worn surface and their flow behaviour at large strains has a clear effect on wear resistance. In this study, the characteristics of the near-surface region of a ferritic-pearlitic steel (0.2% C, 1.2% Mn), subjected to abrasive wear tests, were examined. Wear tests were performed under different loads by rubbing the specimens on sliding 60 mesh Al₂O₃ abrasive band. The metallographic technique used to determine the magnitude of plastic deformation was based on measurement of the displacements of pearlite bands. The hardness of the plastic deformation zone was determined by performing ultramicrohardness tests along ferrite bands with a Vickers indenter. Microscopic examinations of the near-surface regions revealed the wear mechanism to be ploughing and the deformation mechanism to be cross-slip. It was observed that plastic strain (more than 6) occurred on the abraded surface, and increased the hardness to about 1.5 times the original value. The strain and hardness gradient extended to a larger depth into the bulk with increasing wear test load. It is concluded that the wear resistance of the investigated steel increases by work hardening of the near-surface region which is required to consume high energy for abrasion, during sliding. Ultramicrohardness measurements performed on worn specimens revealed high hardness, as the indent size decreased. The indentation size-hardness relation was explained by a dislocation model incorporating geometrically necessary dislocations due to the presence of strain gradients in the deformation region around the indent.     

Effects of particle size, polishing pad and contact pressure in free abrasive polishing

The objective of this research is to better understand the mechanisms of material removal in the free abrasive polishing process. Experiments were carried out to understand the effects of particle size, polishing pad and nominal contact pressure on the wear rate and surface roughness of the polished surface. A theoretical model was developed to predict the relationship between the polishing parameters and the wear rate for the case of hard abrasive particles sandwiched between a soft pad and a workpiece (softer than the abrasive particles). Experimental results and theoretical predictions indicate that the wear rate increases with an increase in particle size, hardness of polishing pad and nominal contact pressure, and with a decrease in elastic modulus of the polishing pad. Surface roughness increases with an increase in particle size and hardness of polishing pad, and nominal contact pressure has little effect on the roughness. A dimensionless parameter, wear index which combines all of the preceding parameters, was introduced to give a semi-quantitative prediction for the wear rate in free abrasive polishing. It is also suggested that when polishing hard material, in order to achieve a high materials removal rate and a smooth surface, it is preferable to use diamond as the polishing particles because of their high deformation resistance.     

The effect of surface hardness on friction

The influence of bulk hardness, surface hardness and strain-hardening rate on the frictional behavior of Cu-Sn and Cu-Al alloys was investigated. Unlubricated specimens were subjected to severe relative sliding against tool steel (D2) and aluminum bronze (Ampco 25) anvils under constant interference conditions. A microindentation hardness survey, from the surface into the bulk, was carried out on sections of the specimens both before and after testing.The highest hardness was measured immediately below the wear surface; this hardness value was found to increase linearly with an increasing instantaneous strain-hardening rate. However, no correlation could be detected between the coefficient of friction and the bulk hardness, the strain-hardening rate or the surface hardness. There was a general trend for the coefficient of friction to increase with the greater increase in hardness produced during sliding against Ampco 25. Drawing on observations of metal transfer and surface damage made earlier, this increase could be attributed to the formation of junctions that were stronger than the parent material. There was no correlation with hardness increase when sliding against D2 and the coefficient of friction was often, but not always, lower. Thus a hardness increase during sliding led to increasing friction only with the metallurgically highly compatible pairs while differences in compatibility rather than hardness increase governed the magnitude of friction with less compatible pairs.     

Determination of the wear resistance of traditional ceramic materials by means of micro-abrasion technique

Micro-abrasion techniques enable the surface wear of materials to be studied with greater precision than provided by other methods. In addition to their reliability, micro-abrasion techniques allow the wear phenomenon of the top-most layers to be studied while assuring, in the case of thin coatings, that this is not influenced by the substrate.In the present study, micro-abrasion technique (cratering with a steel ball) was used to determine the wear resistance of traditional ceramic materials, as a complementary test to the methodologies on a macroscopic scale that are customarily used for this type of material. In order to adapt the test to these materials, the individual effect of each test condition on wear resistance was isolated, while keeping the other conditions constant. The following variables were studied: diameter and angular velocity of the ball, abrasive suspension feed rate and grain size, sample–ball contact angle and groove in the supporting drive shaft. The values established were validated by performance of the test on materials of a glassy nature.The micro-abrasion test is shown to be a useful method for studying wear performance of ceramic glazes.     

Micro-scale abrasive wear testing of duplex and non-duplex (single-layered) PVD (Ti,Al)N, TiN and Cr–N coatings

A micro-scale abrasive wear test, based on ball-cratering, has been used to evaluate the wear resistance of duplex and non-duplex (Ti,Al)N, TiN and Cr–N coatings. The term duplex is used here when plasma nitriding is followed by PVD coating. Coatings without the plasma nitriding stage are termed single-layered. Coating properties were evaluated by surface profilometry, hardness and scratch testing. All duplex coatings showed higher micro-abrasive wear resistance than their single-layered counterparts, with the duplex (Ti,Al)N coating achieving the best performance. After a certain number of ball revolutions, the coating material became worn through, exposing the substrate material. After this point, the presence of a hard nitrided case diminished the scratching action of the SiC abrasive particles. The experimental results also indicate that the choice of the PVD coating plays an important role in improving the micro-abrasive wear resistance. Apart from single-layered and duplex Cr–N coatings, all the other coating systems provided a higher micro-abrasive wear resistance than the uncoated substrate (hardened AISI H13 steel). The poor abrasive wear resistance recorded for the single-layered and duplex Cr–N coatings could be attributed to the hardness of the Cr–N being much lower than that of the SiC abrasive particles, which caused tearing of the coating with subsequent delamination. The wear pattern observed was found to change from surfaces characterised by grooves (uncoated substrate, single-layered TiN and Cr–N systems and duplex Cr–N system) to surfaces which exhibited multiply indented surfaces (single-layered and duplex (Ti,Al)N systems), indicating a transition between wear mechanisms. This transition was found to be dependent on the ratio between the hardness of the SiC abrasive particles and surface (coating) or subsurface hardness. By decreasing this ratio, the ability of the SiC abrasive particles to scratch the composite surface was reduced and the resistance to micro-scale abrasion was improved.     

Tempering temperature effects on abrasive wear of mottled cast iron

The effects of different tempering temperatures (300–600 °C) on abrasive wear resistance of mottled cast iron were studied. Abrasive wear tests were carried out using the rubber-wheel test on quartz sand and the pin test on Al₂O₃ abrasive cloths. The retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of the specimens was examined by scanning electron microscopy for identifying the wear micromechanism. Bulk hardness and matrix hardness before and after the tests were measured. The results showed that in the two-body (pin-on-disc test) system, the main wear mechanism was microcutting and high matrix hardening was presented. The wear rates presented higher correlation with the retained austenite than with the bulk and matrix hardness. In the three-body system (sand–rubber wheel), the wear surfaces presented indentations due to abrasive rolling. The wear rates had better correlation with both the bulk and matrix hardness (before and after the wear test) than with the retained austenite content. There are two groups of results, high and low wear rates corresponding to each tribosystem, two-body abrasive wear and three-body abrasive wear, respectively.     

Assessing the Tribocorrosion Performance of Three Different Nickel-Based Superalloys

Tribocorrosion, which is a material deterioration caused by the synergistic effect of corrosion and wear acting together, is encountered in many engineering applications. Ni-based superalloys, which are widely used in chemical, petrochemical and nuclear power industries as well as in hot sections of turbine engines, owing to their excellent corrosion resistance, high strength and capability to retain hardness at elevated temperatures, are subjected to corrosive wear in service conditions. Therefore, an understanding of the tribocorrosion behavior of these superalloys allows choosing the right material for specified applications and predicting the material damage. In this study, the tribocorrosion behavior of Hastelloy C2000, Hastelloy G35 and Haynes 625 was studied using different electrochemical test techniques including open circuit potential (OCP) measurement, potentiodynamic and potentiostatic polarization tests under sliding contact in 3.5 wt% NaCl solution. Scanning electron microscopy (SEM) was employed in order to characterize corrosive-wear damage, and the surface profiles of wear tracks were obtained using a high-resolution surface profilometer for calculating wear loss. Also the metal dissolution caused by corrosive wear was detected using an inductively coupled plasma optical emission spectrometer (ICP-OES). Test results indicated that the tribocorrosion performance of superalloys is affected by their elemental composition and microstructural characteristics, which induce changes in mechanical properties. Haynes 625, which has the highest hardness value owing to decreasing grain size, showed less material volume loss than other superalloys in all tests. However, the protective oxide film on Haynes 625 especially thickened in potentiodynamic tests provided inhibition of excessive metal dissolution. Cathodic protection resulted in decreasing material loss, but on the other hand hydrogen intake was observed on cathodically polarized specimens.     

Wear resistance characteristics of materials used in oil sands plants

The surge in demand for natural resources has shifted the focus of the international community toward the development of oil sands, shale oil, shale gas and other non-traditional energy sources. In extreme environments, materials used in petroleum gas plant modules are accompanied by various problems caused by low-temperature brittleness such as damage, corrosion and wear. Many researchers have been conducting studies to discover a suitable material whose lifespan could be improved by performing characteristics analyses and performance assessments. In this study, a material characteristics assessment was conducted based on a wear resistance test on materials that are commonly used at oil sands plants. Prior to a wear resistance test, a chemical composition analysis was performed on each of the specimens, and tensile, impact, hardness and corrosion tests were carried out to examine the correlation between their results with the results of the wear resistance test. Each test was performed according to ASTM G 105 standards, and the change in weight according to wear length was analysed for each material to determine the related tendencies. In addition, the results of the wear test were derived by analysing the change in the mass of the specimen before and after the test, and the surface roughness was assessed to analyse the performance related to wear and define the service life. The aim was to use these results to select a material that would be suitable for the abrasive environment of the key equipment and materials of plants.     

表面强化销轴农用滚子链的磨损试验研究

对农机用滚子链条的主要磨损表面——销轴表面进行化学镀镍、镀硬铬、渗钒不同的表面强化处理,测量了三种销轴表面强化后及国外某公司同规格销轴的表面硬度及硬化层厚度.把三种销轴表面强化的链段与国外同节数的链段组装成一条链条,在LS910A封闭力流试验机上进行对比磨损试验.试验数据表明,在所提供的试验条件下,销轴表面镀硬铬链条具有更好的耐磨性能,优于国外的样品链条.     

Sliding wear behavior of Fe-based bulk metallic glass at high temperature

In the past decade Fe-based bulk metallic glasses (BMGs) have attracted increasing attention due to their beneficial properties, including high glass forming ability (GFA), high strength and hardness and high fracture toughness in both fundamental science and engineering application. Most research using these materials has been conducted at room temperature environment, and research that assesses their behavior especially at high temperature has been scarce. We present the results of high temperature effect on the friction and wear behavior of Fe-based bulk metallic glass (BMG), and we tested that this material may satisfy wear and oxidation resistance at high temperature as well as to explore the high temperature wear mechanism of the Fe-based BMG. The dry sliding tribological behaviors of Febased BMG against Si₃N₄ ceramic were conducted with a pin-on-disc friction and wear tribometer. The morphology of the worn surfaces of Fe-based BMG was examined by scanning electron microscopy (SEM) and the chemical composition characterized with energy dispersive spectroscopy (EDS) to observe the wear characteristics and investigate the wear mechanisms. The overall average friction coefficient value generally decreased with increasing temperature, and the glass transition and the formation of protective oxide film played an important role in the tribological behavior of BMG. The wear resistance of Fe-based BMG was not only from their hardness but also from the formation protective oxide layer. Analysis of the worn surface revealed abrasion, plastic deformation and oxidation during sliding test.     

Wear Mechanisms at High Temperatures. Part 1: Wear Mechanisms of Different Fe-Based Alloys at Elevated Temperatures

To extend the lifetime of the sinter grate used to crush the sinter cake into smaller pieces for steel fabrication, a study was undertaken to investigate which wear processes are primarily responsible for limiting the lifetime of the sinter grate. Several wear processes could be identified. The sinter temperature which is up to 800 °C causes temperature-induced material ageing and oxidation. The falling of the sinter cake onto the sinter grate causes high impacts, erosion and abrasive wear. There is enormous economic pressure, which makes the most cost-efficient solution the most attractive one, not the technically “best” coating material; thus, Fe–Cr–C hardfacing alloys are mostly used. In view of the above, four different alloys which are promising for this application were studied with regard to their wear resistance. Each wear mechanism was investigated in a special test tribometer. Fatigue wear caused by multiple impacts and abrasion was tested in the high-temperature continuous impact abrasion test. Materials behaviour in heavy single impacts was evaluated in the single impact test. Characterisation of microstructure and wear behaviour was performed by optical microscopy and scanning electron microscopy. The results obtained with the help of the different measurement techniques were linked and set into comparison to calculate the volumetric wear of the specimen. Aim of this work was to investigate the influence of the material parameters such as macrohardness, hard phase content, microstructure coarseness on the wear resistance in impact loading and abrasive applications at high temperatures. Results also indicate that the matrix ability to bind carbides at high temperature as well as the matrix hardness at high temperatures strongly influence the wear resistance in the different tests. Those material parameters get correlated to the wear rates in different material demands. The test results indicate that at higher temperatures material fatigue becomes a major wear-determining factor which makes the matrix hardness and the matrix ability to bind carbides at high temperatures very important. Especially, in abrasive wear, a certain content of hard phases is also necessary to keep the wear to a lower level. It could also be shown that in impact loading applications, a coarse microstructure is a disadvantage.