Impact wear of a tool steel

Results from wear studies in repetitive impact sliding are described in this paper. The material pair studied consisted of steel CPM-10V (specimen) (where CPM denotes crucible particle metallurgy) and 17-4 precipitationhardened (PH) steel (counterface) with transverse sliding velocities of 4 and 8 m s^?1. By means of scanning electron microscopy, energy-dispersive analysis of X-rays and X-ray diffraction methods it is shown that the wear is due to a material transport of the counterface 17-4 PH steel to the CPM-10V surface. In the wear process, a change in microhardness of the counterface substrate is apparent, and X-ray diffraction of debris confirms the presence of transformed metal. These products include γ-Fe together with trace amounts of α-Fe₂O₃; however, virtually no carbide from the CPM-10V steel was detected.     

Notes on contributors

Various metallic pairs were tested under conditions of unlubricated solid contact. Experiments were conducted for repetitive impulsive and continuous sliding contact. Wide ranges of materials and conditions (nominal contact stress and relative transverse sliding velocity) and a variety of loading modes (pure normal impact at various frequencies, compound impact at various sliding velocities, and pure sliding under various stress levels) were explored.Particular attention was focused on the establishment of subsurface material zones developed in the tests, in situ. These zones exhibit dependences on velocity, stress, material, test duration and loading mode. The experimental findings, based on several analysis techniques, serve to characterize subsurface zone composition and morphology. Both surface and subsurface features were examined by optical and electron microscopy and analyzed by energy-dispersive X-ray techniques to allow interpretations concerning the role of external parameters, material transport and debris formation, as well as insight into operative mechanisms which act on specific materials under prescribed conditions to cause wear.     

The role of specimen stiffness in sliding and impact wear

The results of pin-on-disc sliding tests and of impact wear tests are presented. Titanium alloy specimens were used for the sliding tests and high strength steel specimens were used for the impact tests: in both types of test stainless steel was the counterface material. The test duration, the nominal contact stress and the effective “stiffness” of the pins were varied; the effective stiffness was varied by changing the unsupported length of the pins while all other experimental conditions were maintained invariant. Experimental data on the wear track depth and roughness, obtained by profilometry, and on the specimen and counterface surfaces, which were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) techniques, are presented: the data include morphological features and material transport observations. Subsurface sections of specimens were analyzed by SEM, EDX techniques and transmission electron microscopy. Characteristic subsurface zones are identified and described with respect to both morphology and composition in the near-surface microstructure. The data clearly indicate that the stiffness is an important factor in experimental work in sliding as well as in impact wear.     

The role of microstructure in the impact wear of two aluminum alloys

The impact wear resistance of two aluminum alloys was investigated using flat-ended aluminum specimens impacted upon a stainless steel counterface. The counterface itself was held stationary in some tests (pure normal impact) and moved transverse to the normal impact direction in other tests (compound impact).The alloys investigated were aluminum-copper: 2011-T3 which was formulated for free-machining applications and 2124 which possessed very high fracture toughness. Thus, one alloy favors crack nucleation and growth, while the other suppresses these. A variety of tests were conducted with both alloys in compound impact loading. The peak impulsive stress was found to influence wear rates significantly; the relative sliding velocity is also an important parameter.Surface and subsurface microscopy were used to define operative wear mechanisms. With the 2011-T3 alloy, the characteristic subsurface features support the delamination theory of wear. With the 2124 alloys, subsurface features differ significantly. These features are discussed in the light of microstructural variations in the alloys.     

Microstructure and Wear Behavior of a Manganese Bronze Bearing Material under Unlubricated Conditions

In an attempt to collect information about the tribological performance of copper-based bearings, the friction and wear behaviors of C86300 manganese bronze were investigated. The characteristics of the base material were determined by structural and mechanical investigations. Then, dry sliding pin-on-disc wear tests were performed against an AISI 52100 steel counterface. After the wear tests, the worn surfaces of the pins and wear debris were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. In addition, light optical microscopy and microhardness measurements were performed for examination of the steel counterfaces and worn pin subsurface layers. With increasing normal load, the wear rate of commercial C86300 alloy (containing 0.6 wt% Si) decreased initially and then began to increase. After reaching a maximum wear rate at the load of about 60 N, the wear rate decreased again with a further increase in the normal load. However, the wear rate of this C86300 alloy mainly decreased with increasing sliding speed. Adhesive and abrasive wear were the dominant wear mechanisms under the designed conditions.     

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.     

Adhesive wear and frictional characteristics of UHMWPE and HDPE sliding against different counterfaces under dry contact condition

Abstract

The current work evaluates the wear and frictional performance of ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) sliding against different metal counterfaces, stainless steel(SS), mild steel (MS) and aluminium (Al), under dry contact condition. The experiments were conducted using pin on disc machine at different sliding distances (0–40·32 km), 15 N applied load and 2·8 m s^–1 sliding velocity. Interface temperatures and frictional forces were measured simultaneously during the sliding, while specific wear rates were determined for every 1·68 km sliding distance. Based on the optical microscopy of the worn surface and wear track, frictional and wear results were analysed and discussed. The experimental results showed that the type of counterface material significantly influences both frictional and wear performances of the selected polymers. This was mainly due to the film transfer characteristics. Higher temperature and friction coefficient for UHMWPE and HDPE were evident when sliding took place against Al counterface. Sliding the polymers against stainless steel showed low friction coefficients compared to other counterfaces.     

Characteristics of wear debris in impact sliding

The characteristics of debris arising from repetitive compound (sliding) impact are presented. The debris was collected from a variety of tests. Microscopy and X-ray diffraction analysis establish (1) that debris may arise from specimen and counterface, (2) that metallic particles consist of very small and/or distorted primary crystals, (3) that oxide formation occurs and (4) that phase transformations of metallic constituents may occur. Further, particular debris characteristics are shown to be dependent on the nominal contact stress and the relative sliding velocity.     

Tribological behaviours of PA/UHMWPE blend under dry and lubricating condition

Dry-sliding and lubricated friction and wear behaviours of polyamide (PA) and ultra-high molecular weight polyethylene (UHMWPE) blend were studied using a pin-on-disc method (polymer pin sliding against a stainless steel disc) at room environment. The tribological performance of PA and UHMWPE were also investigated for the purpose of comparison. The worn surfaces were examined using a scanning electron microscope (SEM) and optical microscope. It was observed that PA specimen demonstrated highest friction coefficient, UHMWPE the lowest in both dry-sliding and lubricated sliding test. The friction of PA could be sufficiently decreased by blending with UHMWPE. Statistical analysis suggested the relationship between the wear volume loss and the sliding distance could be expressed by a linear model for dry-sliding, while a logarithmic model was determined for lubricated sliding. The difference in wear modes between both sliding series suggested that there was change in the mode of material removal process. The lower wear rate in lubricated sliding was attributed to the elastohydrodynamic or partial elastohydrodynamic lubrication through the development of a continuous lubricant film between the polymer and the counterface, while the high wear rate of the specimens, in dry-sliding test, was mainly caused by fatigue process due to the repeated action of tearing and crack-propagation.     

Friction and Wear Behavior of Ultra-High Molecular Weight Polyethylene Sliding Against GCr15 Steel and Electroless Ni–P Alloy Coating Under the Lubrication of Seawater

The friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against GCr15 steel and electroless Ni-P alloy coating under the lubrication of seawater was investigated and compared with that under dry sliding and lubrication of pure water and 3.5 wt.% NaCl solution, respectively. It was found that under the lubrication of aqueous medium, the friction and wear behavior of UHMWPE mainly depended on the corrosion of counterface and the lubricating effect of the medium. Because of serious corrosion of counterface by the medium, the wear rates of UHMWPE sliding against GCr15 under the lubrication of seawater and NaCl solution were much larger than that under other conditions, and such a kind of wear closely related to the corrosion of counterface can be reckoned as indirect corrosive wear. However, when sliding against corrosion-resistant Ni–P alloy under the lubrication of seawater, the lowest coefficient of friction and wear rate of UHMWPE were obtained, owing to superior lubricating effect of seawater. Moreover, periodic ripple patterns were observed on the worn surfaces of UHMWPE sliding against GCr15 under the lubrication of seawater and NaCl solution, which were ascribed to the intelligent reconstruction of surface microstructure of UHMWPE upon large plowing effect of the counterface asperities. Based on scanning electron microscopic (SEM) and three-dimensional (3D) profile analyses of the worn surfaces of UHMWPE, a stick–slip dynamic mechanism was proposed to illustrate the pattern abrasion of UHMWPE. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Tribological performance of A206 aluminum alloy containing silica sand particles

The dry-sliding tribological behavior of A206 aluminum alloy containing silica sand was investigated using a three pin-on-disk tribometer against an SAE 1045 steel counterface. The worn surfaces of the pins were then analyzed by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). The test results showed that the addition of silica sand particles decreased the friction coefficient of Mg modified A206 alloy. The wear rate of the composites increased with increases in the applied pressure from 0.35 to1.75 MPa and with increases in the silica sand content from 0% to 13%. The wear rate variation with the applied pressure is attributed to the shift in the dominant wear mechanisms from oxidation and mild abrasive wear at applied pressures at and below 0.35 MPa to delamination accompanied by severe abrasive wear at applied pressure levels above 0.35 MPa. The high wear rate may be as a result of an overall decrease of the fracture toughness of the composites containing silica particles. The temperature near the counterface surface increased with increases in both silica content and the applied pressure due to the lower thermal conductivity of silica sand and greater abrasion that occurs at higher silica contents. A T6 heat treatment did not significantly decrease the friction coefficient or the wear rate of either the A206 matrix alloys or the composite containing silica sand.     

Reciprocating Sliding Wear Performance of Hard Coating on Modified Titanium Alloy Surfaces

The high strength, low weight, and outstanding corrosion resistance properties possessed by titanium alloys have led to a wide range of successful applications in aerospace, automotive, and chemical industries and in power generation. Titanium alloys are characterized by poor wear resistance properties and their utilization has been excessive in nontribological applications. Surface texturing is a well-known and effective means of surface modification to improve the tribological properties of sliding surfaces. In the present work, modification of titanium alloy surfaces (Ti6Al4V) was done by lapping and laser surface texturing. The wear-resistant coating, AlCrN, was applied over the modified titanium alloy surfaces, with and without a chromium interlayer. Linear reciprocating sliding wear tests were performed with ball-on-flat contact geometry to evaluate the tribological performance of the coated alloy. The tests were performed under different normal loads for a period of 105 cycles at a frequency of 5 Hz. The friction force between the contact pair and displacement of the ball were simultaneously observed using a force transducer and laser displacement sensor. Optical microscopy was used to quantify the wear volume by measuring the wear scar diameter on both the specimen and the counterbody. Scanning electron microscopy (SEM) was employed to study the morphology of the wear scar. The characteristic behavior of the AlCrN coating such as bonding strength, wear volume, wear rate, and coefficient of friction with the chromium interlayer was evaluated and compared with the coating directly applied over the substrate. The coating on the textured surface, with the chromium interlayer showed better tribological performance.     

Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes has renewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titanium against various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titanium alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainless steel, silicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate were lower at the higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the highest to the lowest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to their relative fracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counterfaces and suggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which adhere to the ceramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactions along with the fracture toughness dependency helped explain the high wear on the ceramic sliders.     

Specimen-counterface bulk hardness effects in impact wear of 17-4 PH steel pairs

Impact sliding wear tests have been performed with 17-4 PH steel as both specimen and counterface material. Tests were designed to explore the influence of bulk hardness; this was done by contacting hard pins against soft discs and vice versa. Additional wear tests were conducted with specimen and counterface of equal hardness. The entire program employed four distinct microstructural conditions in the hardness range from 30 to 44 HRC. The results indicate that for the test conditions explored the wear rate of the specimens (pins) depends on the “hardness pair” while the counterface (disc) wear does not. It was further shown that changes in specimen geometry (mushrooming) are of major relevance. The subsurface sections from the pins and discs formed characteristic zones of plastic deformation and mechanochemical mixing. In this, the hardest pin-softest disc and softest pin-hardest disc pairs developed essentially the same near-surface zone on the counterface, irrespective of initial microstructural condition.     

Friction and dry sliding wear behavior of carbon and glass fabric reinforced vinyl ester composites

Friction and dry sliding wear behavior of glass and carbon fabric reinforced vinyl ester composites have been presented. The results show that the coefficient of friction and wear rate increased with increase in load/sliding velocity and depends on type of fabric reinforcement and temperature at the interphase. The excellent tribological characteristics were obtained with carbon fiber in vinyl ester. It is believed that a thin film formed on counterface was seems to be effective in improving the tribological characteristics. The worn surfaces examined through SEM, showed higher levels of broken glass fiber in vinyl ester compared to carbon-vinyl ester composites.     

Tribological Characteristics of Sustainable Fiber-Reinforced Thermoplastic Composites under Wet Adhesive Wear

The friction and specific wear rate of sustainable kenaf fiber–reinforced polyurethane composites were investigated against stainless steel counterface and under wet contact conditions. The new composites were evaluated at different applied loads (50–80 N), sliding distances (up to 2.7 km), and fiber mat orientations. Scanning electron microscopy (SEM) was used to observe the damage features on the worn surfaces. The results revealed that sustainable kenaf fibers assisted in enhancing the wear and frictional performance of the polyurethane thermoplastic composite by about 59 and 90%, respectively. Operating parameters and mat orientation controlled the wear and the frictional behavior of the composite. Better wear performance was exhibited at high loads and when the fiber mats were oriented perpendicularly to the sliding direction. Observations of the worn surfaces revealed different features of damage such as microcracks, fiber tearing, fiber detachment, and delamination. However, there was no trace of fiber pull-out in any of the tested conditions.     

Friction and wear of Cu-Ni alloys

The friction and wear of Cu-Ni alloy blocks sliding against 440C and coated steel rings have been studied. Sliding speed was 50 mm s^?1 and test atmospheres were argon and dry air. A wide range of experimental techniques was used to characterize the worn specimen and the debris particles. X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis of X-rays have been particularly helpful. Transfer of ring material was observed in most cases, especially when the debris particles were ferromagnetic. The wear rates of the Cu-Ni blocks are largely determined by the amount of transferred ring material. The wear rates of the Cu-Ni alloys decrease with increasing transfer of ring material. However, the wear rate of the ring increases as transfer continues. This process often leads to a transition involving severe damage to the ring. Brushes which remove most of the loose debris significantly reduce transfer and postpone the transition.     

The friction and wear behaviour of nickel-base alloys in air at room temperature

Measurements are presented of the friction and wear during sliding of specimens of Nimonic 75, C263, Nimonic 108 and Incoloy 901 on like specimens in air nominally at room temperature. The worn specimens have been examined using microhardness measurements, optical and scanning electron microscopy, X-ray diffraction and electron diffraction. These techniques suggest mechanisms for the room-temperature wear of these alloys associated with their strength properties. In particular, changes in the coefficient of friction and the wear rate during sliding can be correlated with work hardening, and possibly some degree of age hardening, of the load-bearing areas, due to the severe mechanical and thermal stresses developed. There is no evidence that oxide films formed on the contact areas during sliding have a significant effect on the tribological behaviour of these alloys. Such films are merely removed from the surface as wear debris.     

Investigation of the Transition State in the Wear of Polyphenylene Sulfide Sliding Against Steel

The effect of sliding variables, including counterface roughness, sliding speed, and contact pressure, on the run-in state of wear and friction was studied. Sliding was performed in the pin-on-disk configuration with a polyphenylene sulfide (PPS) pin resting on the flat steel counterface. Some experiments were also run to study the effect of air cooling and heating. Optical microscopy and scanning electron microscopy were used to study the shape and size of the wear debris, worn pin surface, and the transfer film formed on steel counterfaces. It was found that friction and wear in the run-in state were significantly affected by the sliding variables studied and their influence was closely related to the development of a transfer film during the run-in state. If the transfer film developed during initial sliding, the coefficient of friction increased and wear rate decreased. The wear rate in the run-in state increased with the increase in initial counterface roughness and there was an optimal counterface roughness of 0.06 m Ra for minimum steady state wear rate. A higher applied load led to a higher wear rate in the run-in state but that was not the case with steady state wear rate.     

Friction and Wear Studies of Octadecyltrichlorosilane SAM on Silicon

A self-assembled monolayer of octadecyltrichlorosilane (OTS) was prepared on a single-crystal silicon wafer (111) and its tribological properties were examined with a one-way reciprocating tribometer. The worn surfaces and transfer film on the counterface were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that, due to the wear of the OTS monolayer and the formation of the transfer film on the counterpart ball, the friction coefficient gradually increases from 0.06 to 0.13 with increasing sliding cycles and then keeps stable at a normal load of 0.5N. The transfer film is characterized by deposition, accumulation, and spalling at extended test duration. Though low friction coefficients of the monolayer in sliding against steel or ceramic counterfaces are recorded, poor load-carrying capacity and antiwear ability are also shown. Moreover, the monolayer itself or the corresponding transfer film on the counterface fails to lubricate even at a normal load of 1.0N. Thus, the self-assembled monolayer of octadecyltrichlorosilane can be a potential boundary lubricant only at very low loads.