Wear of some F.C.C. metals during unlubricated sliding part II: effects of normal load,sliding velocity and atmospheric pressure on wear fragments

The effects were determined of normal load, sliding velocity and atmospheric pressure on the volume and the formation rate of wear fragments obtained by experiments with Ni, Cu and Au under unlubricated conditions. The results show that the volume and the formation rate change in different ways. The change of wear with normal load or sliding velocity is predominantly due to a change in the volume of fragments. The change in wear with atmospheric pressure is due to a change of the formation rate. It is concluded that the volume of wear fragments is governed mainly by some mechanical factors and that the formation rate is dependent on chemical factors such as the chemisorption of oxygen.     

Frictional behavior of sputtered TiN

In this research, reciprocating sliding experiments were conducted on films of sputtered TiN. The primary emphasis was to evaluate the effect of the applied film thickness on the friction coefficient. Other parameters namely, surface roughness, substrate hardness and applied load were also varied and their effects were studied. From the friction data and the results of the microscopy studies, the dominant mechanism responsible for the transition and steady state friction behavior were evaluated.The results show that the gradual accumulation of minute wear fragments followed by the formation of a rigid transferred layer are responsible for the transition of the friction coefficient. During the steady state, sliding is occurring between the slider and a small portion of the transferred layer. The steady state friction coefficient varies with the applied coating thickness under the light load. Under the heavy load the coating thickness has no effect on the friction coefficient, except that the friction coefficient tends to be lower for the minimum film thickness.     

Transfer during unlubricated sliding wear of selected metal systems

Results of pin-on-disk sliding tests in vacuum, with copper, CuNi, nickel and molybdenum sliding against iron, indicate that initial transfer events involve discrete fragments. We propose that the process involved in the initial transfer events is a consequence of local shear instabilities which develop at large plastic strains. In copper samples the initial transfer elements are lamellar, with layer thickness equal to the cell thickness in the highly deformed base material adjacent to the sliding interface.Prolonged sliding gives rise to the formation of transfer layers or patches on the specimen surface. These layers or patches are composed of finely mixed material derived from the two sliding counterparts as well as scattered pieces of more recently transferred fragments. Typical wear debris particles are generated from the transfer layers or patches.Transfer tendencies for different materials combinations can be predicted from an adhesion point of view if geometrical effects are properly considered. Combining theoretical predictions of transfer tendencies and experimental observations of transfer and geometrical effects, one finds that for a pin-and-disk system the disk should be made of the material having the higher cohesive strength.     

Effect of MoO3 Tabular Crystals on TiAl Matrix Composites under Different Test Loads

The friction and wear behavior of TiAl matrix self-lubricating composites (TMSCs) with MoO₃ tabular crystals (MTCs) sliding against a GCr15 steel ball is tested using a constant speed of 0.2 m/s at room temperature under different loads from 6.65 to 16.65 N. The result reveals that TMSCs show a consistently lower friction coefficient in a certain range from 0.2 to 0.6 and less wear rate from 0.29 × 10^?4 mm³ N^?1 m^?1 to 0.49 × 10^?4 mm³ N^?1 m^?1 compared to TiAl-based alloy. Moreover, the friction coefficient and wear rate of TMSCs decrease with an increase in test load. MTCs in the deformed layer will be refined to produce interfacial shear slip and reduce the shear stress because of the weak binding force of MTCs in the sliding process, which can facilitate the formation of a deformed layer and protect the deformed layer from spalling failure. In addition, MTCs on the worn surface of TMSCs can reduce the shear stress directly. Hence, MTCs can promote antiwear of the deformed layer and reduce the friction on the worn surface of TMSCs. MTCs can play a better role in antiwear and antifriction when the test load is higher.     

Transfer of semicrystalline polymers sliding against a smooth steel surface

The interrelationships between transfer and wear in polymers were studied using a pin-disk-type wear testing apparatus. The wear rates of polymers except polytetrafluoroethylene (PTFE) were high for up to about the first 100 revolutions of the disk and decreased gradually until the steady low wear rates which generally occurred after about 2000 revolutions. However, PTFE exhibited an almost constant high wear rate throughout the wear process. The thickness of transferred polymer increased rapidly with increasing number of revolutions in the initial wear stage but after about several hundred revolutions remained constant. A coherent transfer film was formed in most parts of the friction track after about 100 revolutions. It was found that polymer wear could occur in polymers sliding on a transferred polymer layer. All polymers except PTFE exhibited smaller wear rates when sliding on the transferred layer. The load dependence of the thickness was very small compared with that of the wear rate. PTFE produced a very dense and coherent transferred layer compared with that of other polymers. However, there was no clear relationship between friction and the thickness of the transferred polymer layer.     

Investigation of mechanical and tribological properties of tribo‐layer of Ni3Al matrix composites

The sliding wear of Ni₃Al matrix composites with addition of 1.5 wt.% graphene nanoplates was studied through pin‐on‐disc wear testing. The spontaneous formation of a tribo‐layer produced during sliding wear was found to result in a deviation from Archard scaling and an unexpected high wear resistance that was not based on hardness alone. The tribo‐layer exhibited specific microstructural evolution with significant severe deformation and grain refinement after wear. In the grain refinement area, the accumulation of dislocations and an increase in misorientations were found to lead to strain hardening. For the plastic deformed area, reduction in the dislocation density inside the elongated ultrafine grains reduced strain hardening compared with the grain refinement area. It can be concluded that the deviation from Archard scaling occurred primarily as a result of the microstructural evolution of the tribo‐layer, resulting in the specific performance of mechanical and tribological properties of Ni₃Al matrix composites under cyclic sliding wear process. Copyright © 2016 John Wiley & Sons, Ltd.     

Dry Sliding Wear Behavior and a Proposed Criterion for Mild to Severe Wear Transition of Mg–3Al–0.4Si–0.1Zn Alloy

Wear behavior of Mg–3Al–0.4Si–0.1Zn alloy was studied as a function of applied load and sliding speed under dry sliding conditions using a pin-on-disk configuration within 20–380 N and 0.1–4.0 m/s. An empirical wear transition map has been constructed to delineate the conditions under which severe wear initiated. The roles of microstructural evolution, hardness change in subsurface and surface oxidation on wear transition were also studied. The results indicate that the transition to severe wear occurs when the deformed microstructure in surface layer of material transforms into dynamic recrystallization (DRX) microstructure. A contact surface DRX temperature criterion for mild to severe wear transition is proposed, and the contact surface DRX temperatures are calculated using activation energy obtained by hot compression tests. A model for predicating mild to severe wear transition load has been developed based on the proposed contact surface DRX temperature criterion. The mild to severe wear transition loads are well predicted within the sliding speed range of 0.8–4.0 m/s.     

The effect of rolling direction reversal on the wear rate and wear mechanism of pearlitic rail steel

The effect of different single and multiple rolling direction reversal (RDR) regimes on wear rate and mechanism is studied in this paper. Changes in structure deformation morphology and accumulated plastic strain are also analysed. Evidence that unidirectional rolling sliding contact can result in directional mechanical properties of the deformed layer is given. Results obtained under the test conditions used show that RDR has a beneficial effect on the wear rate of pearlitic rail steel. Multiple short RDR resulted in the lowest wear rate, less than half the unidirectional value.     

Effect of wear on EHD film thickness in sliding contacts

A theoretical solution to the elastohydrodynamic (EHD) lubrication problem in sliding contacts, which takes into consideration the effect of the change in shape of the gap due to wear on the load‐carrying capacity, is presented. The model of such a contact is based on assumptions of Grubin and Ertel (von Mohrenstein). The resultant dimensionless Reynolds and film profile equations have been solved numerically for a number of cases with several values of thickness of the worn layer. Iteration of the EHD film thickness is performed by means of the secant method. Values of the calculated dimensionless film thickness are presented as a function of dimensionless wear. The conclusions concern the influence of the linear wear on the film thickness in heavily loaded sliding contacts. Copyright © 2006 John Wiley & Sons, Ltd.     

Binder extrusion in sliding wear of WC-Co alloys

It has previously been proposed that preferential removal of the cobalt binder is an important mechanism in the abrasive wear of cemented carbides in the WC-Co family. It is here demonstrated that binder extrusion occurs also in metal-to-metal sliding wear contacts. The wear scar generated by sliding a hardened steel ball repeatedly over a polished WC-Co surface was studied by scanning electron microscopy. The extruded cobalt fragments accumulate at surface defects, such as cracks caused by the sliding loaded ball, and gradual microfragmentation of the carbide grains follows. The energy required to extrude the cobalt and to cause the gradual change in surface layer microstructure is provided by the frictional forces.     

Surface behaviour of as-Cast Al–Fe intermetallic composites

In order to produce energy-efficient material for tribological applications, Al–Fe inter-metallic composites have been produced by liquid metallurgy route. Iron content of the composites varies from 1.67 to 11.2 wt.%. These composites have been tested for their wear properties at different parameters. Debris and wear tracks have been studied in detail to see the surface effects during dry sliding and have been correlated to wear properties. Observations show that low loads and sliding velocities are dominated by oxidative debris and largely covered wear track surface with smooth oxide layer is observed. Whereas metallic debris dominates at higher loads and sliding velocities and highly deformed wear track surface with deep grooves and gross delamination were observed. Further, wear rate is seen to increase continuously with load whereas with sliding velocity it attains a minima after initial decrease and then increases continuously. Low solubility of iron supports the formation of FeAl₃ and an increase in hardness from 95 to 179 VHN continuously improves the wear resistance with increase in percentage iron.     

Tribological Behavior of Ti3Al2.5V Alloy Sliding against EN-31 Steel under Dry Condition

This article aims to study the friction and wear behavior of Ti3Al2.5V alloy sliding against EN-31 steel under dry condition using a multi-tribotester. The effect of variation in load and sliding velocity on wear rate, average coefficient of friction, and contact temperature has been studied and analysis of wear debris has been carried out. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to study the morphology of the wear tracks and deduce microchemical information at the elemental level of worn samples, respectively. Results reveal that the wear rate of Ti-3Al-2.5V increases with increasing sliding velocity and increasing normal load with few exceptions. The average coefficient of friction decreases as the normal load increases with exceptions at some loads. SEM micrographs of worn samples obtained at different loads and sliding velocities show the formation of wear tracks on the surface due to ploughing and flaking of the matrix. The main mechanism responsible for wear of Ti3Al2.5V alloy sample is rupture of the matrix and abrasion. Wear debris analysis shows irregular-shaped wear particles with very sharp edges that appeared to be plastically deformed at high sliding velocity, whereas the wear debris is very loose and fine at lowest sliding velocity.     

The structure of copper rubbed on emery paper at different temperatures

The physical process involved in the rubbing of copper on emery paper resembles the dry sliding wear of copper against SAE 1045 steel. In both cases the top layer of the contact surface, the thickness of which is different for the two processes, is heavily deformed. The heavily deformed material can recrystallize dynamically in accordance with the Zener-Hollomon parameter. When copper undergoes this process at room temperature at high strain rate and high strain, very small grains are formed in the top layer of the rubbed surface. At liquid nitrogen temperature the copper partially recrystallizes dynamically in accordance with the Zener-Hollomon parameter. The occurrence of dynamic recrystallization results in a surface layer with very low residual stresses, high toughness and high hardness. These qualities are desirable in manufactured surfaces.     

Effects of Normal Load,Sliding Speed,and Surface Roughness on Tribological Properties of Niobium under Dry and Wet Conditions

The effects of normal load, sliding speed, and surface roughness on the friction and wear of high-purity niobium (Nb) during sliding without and with an introduction of water were systematically investigated. Increasing the normal load or sliding speed decreased the friction of the Nb under the both dry and wet conditions because the increased wear of the Nb decreased the interfacial shear strength between the steel ball and Nb by promoting the surface roughening and the production of wear debris. However, the Nb tested at the lowest sliding speed under the lowest normal load with water exhibited the lowest friction and wear due to the formation of oxide layer on the wear track. The friction and wear of the Nb tested under the dry condition decreased with increased surface roughness because the higher interfacial shear strength between the steel ball and smoother Nb resulted in the earlier breakdown of the native oxide layer and direct contact between the steel ball and Nb. However, increasing the surface roughness of the Nb increased its friction and wear under wet conditions, probably due to the easier breakdown of the oxide layer that formed on the rougher surface during sliding. The tribological results clearly showed that the introduction of water during sliding had a significant influence on the tribological properties of the Nb.     

Sliding wear behavior of nanocrystalline nickel coatings: Influence of grain size

In the present study the sliding wear behavior of pulse electrodeposited nanocrystalline Ni coatings as a function of grain size including bulk annealed Ni has been systematically studied using pin-on-disc configuration against the WC-Co counter body. The sliding wear has been analyzed with respect to wear rate, coefficient of friction, subsurface deformation and composition of wear debris. The result indicates that the sliding wear rate and coefficient of friction of Ni decreases with decreasing grain size. The subsurface beneath the worn pin surface is composed of a near surface shear region and beneath it a region of bulk plastic deformation. The ratio of the depth of the shear region to the depth of bulk deformed region decreases with decreasing grain size indicating a greater localization of near surface deformation with decreasing grain size.     

Effects of microstructure and experimental parameters on high stress abrasive wear behaviour of a 0.19 wt% C dual phase steel

The present investigation is aimed at understanding the influence of the size and quantity of ferrite plus martensite on mechanical and abrasive wear properties in a 0.19 wt% C dual phase steel. The results indicate that the mechanical properties like strength, ductility and impact, as well as abrasion resistance of the samples are greatly influenced by the material and test conditions. For example, the samples involving prior annealing showed higher ductility but less strength over the normalized specimens. Also, the increasing intercritical annealing temperature led to superior strength associated with reduced ductility. The wear rate increased with load and abrasive size due to a larger depth of cut made by the abrasive medium. The wear rate decreased as sliding distance increased. The steel subjected to prior normalizing treatment attained superior wear resistance to that of the one subjected to prior annealing treatment. The wear rate also decreased with increasing intercritical annealing temperature from 765 to 805 °C with an exception that the steel treated at 805 °C exhibited wear rate comparable to the one treated at 765 °C when tested against coarser size (40 μm) abrasive.     

Estimation of wear particle thickness in polymermetal sliding

Sliding experiments between polymer pins and a steel disc were performed to study the size distributions of polymer wear particles with varying loads and also to estimate the thickness of these particles. Optical microscope examination of the loose wear particles revealed that they resembled a flattened ellipsoid in shape and their size was not strongly dependent on load. The thickness of the wear particles was estimated from an analysis based on a model in which the effect of both the normal and shear stresses on the junction as well as the surface energy of the particle material was considered. It was found that the thickness lies in a range the lower and higher values of which depend upon whether the particle escapes from the interface as soon as it is formed or is trapped between the sliding surfaces before it escapes from the interface.     

Mechanical and tribological properties of vapour deposited low friction coatings on Ni plated substrates

Soft steel and aluminium substrates with load-carrying layers of electroplated nickel were coated with commercially available low friction vapour deposited coatings. The mechanical and tribological properties of the coating and substrate composites were evaluated with special emphasis on the influence of the nickel layer. Two different thicknesses of the intermediate load-carrying nickel layer were tested. The samples were evaluated regarding friction and sliding wear, abrasive wear, hardness and elastic modulus, morphology and coating thickness and adhesion between substrate and coating. It was found that all the evaluated low friction coatings were possible to be successfully deposited on the intermediate nickel layer. A relatively thick intermediate nickel layer is a promising candidate for improvement of the load-carrying capacity.     

The influence of the nitriding process on the dry wear resistance of 15-5 PH stainless steel

The dry wear resistance of 15-5 PH stainless steel nitrided using various methods was investigated. The methods included gas nitriding in cracked ammonia, plasma or ion nitriding and ion implantation of nitrogen. The dry wear resistance and the topography of the wear surface were studied as a function of load and sliding distance. It was found that the wear resistance of the plasma-nitrided specimens is higher than that of the gas-nitrided specimens. The wear resistance of the ion-implanted specimens was even better. However, because of the very small thickness of the implanted layer, only partial results were obtained.     

钢基钒铬铸渗层干滑动磨损特性研究

采用MM-200磨损试验机,研究了不同钒铁颗粒含量的钒铬铸渗层干滑动磨损特性。研究结果表明:在试验条件下,铸渗层的耐磨性能比ZG310-570相比大幅度提高。铸渗层中铬铁含量为35%、钒铁含量为40%的试样耐磨性能最好,在450 N载荷下是ZG310-570的16.5倍。铸渗层的干滑动磨损机制为磨粒磨损和剥层磨损,当载荷较低时,主要以磨粒磨损为主,而载荷较高时,剥层磨损现象有所增加。