Primary Wear Mechanism Research Articles

A physically-based abrasive wear model for composite materials

A simple physically-based model for the abrasive wear of composite materials is presented based on the mechanics and mechanisms associated with sliding wear in soft (ductile)- matrix composites containing hard (brittle) reinforcement particles. The model is based on the assumption that any portion of the reinforcement that is removed as wear debris cannot contribute to the wear resistance of the matrix material. The size of this non-contributing portion (NCP) of reinforcement is estimated by modeling three primary wear mechanisms, specifically, plowing, cracking at the matrix/reinforcement interface or in the reinforcement, and particle removal. Critical variables describing the role of the reinforcement, such as relative size, fracture toughness and the nature of the matrix/reinforcement interface, are characterized by a single contribution coefficient, C. Predictions are compared with the results of experimental two-body (pin-on-drum) abrasive wear tests performed on a model aluminum particulate-reinforced epoxy-matrix composite material.

Cylinder Liner Surface Analysis During SI Engine Break-In

Surface texture of an engine cylinder liner at the top-ring reversal point was observed by using Scanning Electron Microscopy (SEM) and optical microscopy. Experiments were conducted on a single-cylinder spark ignition engine over the engine break-in period. The surface texture of the cylinder liner was observed before and after the break-in test. The changes of surface texture and the wear mechanisms during the engine break-in were analyzed. The primary wear mechanisms were found to be abrasion and plastic deformation. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

Tool life when high speed ball nose end milling Inconel 718™

Following a brief introduction of high speed machining (HSM) and the machinability of Inconel 718, the paper details experimental work using TiAlN and CrN coated tungsten carbide ball end mills, operating at cutting speeds up to 150 m/min. Inconel 718 is one of a family of nickel based superalloys that are used extensively for gas turbine applications requiring high temperature strength. It is an extremely difficult material to machine, not the least, because it maintains much of its strength at elevated temperatures (∼600°C), has low thermal conductivity and is prone to work harden during cutting. A 3 factor, full factorial cutting experiment at two levels is outlined with the workpiece inclined at 45° and 60° from the horizontal. The longest tool life was obtained when operating at 90 m/min cutting speed with TiAlN coated products. The choice of tool coating was the main factor influencing tool life. The primary tool wear mechanism was adhesive wear, which affected the CrN coating to a greater extent. This was accompanied by peeling off the coating to expose the K10 carbide substrate. Irrespective of the tool coating, notches developed close to the depth of cut position. With the workpiece orientated at 60°C, greater tool deflection occurred which exacerbated notch wear and edge chipping.

All-steel and Si 3N 4-steel hybrid rolling contact fatigue under contaminated conditions

Ball-on-rod rolling contact fatigue experiments were performed using M50–M50 all-steel and Si 3N 4–M50 hybrid components, respectively. Experiments were performed using a jet turbine engine lubricant in the as-received condition or with particulate contaminants added. The added particulate contaminants were Arizona test dust or glycothermally synthesized α-Al 2O 3. Wear performance of the all-steel and hybrid rolling systems was evaluated with and without particulate contaminants in the lubricant. Wear surfaces were analyzed using optical microscopy, scanning electron microscopy, surface profilometry, and atomic force microscopy. Wear mechanisms, volume specific wear rates and modes of failure were determined for all systems. The primary wear mechanism produced in rolling contact fatigue experiments is shown to be contact stress fatigue, with secondary mechanisms of indenting, cutting, plowing and embedding occurring as particulate debris passes through the elastohydrodynamic lubricant layer between the ball and rod surfaces.

Effect of grain size on wear behaviour of alumina cutting tools

Pure alumina inserts with grain sizes of 0.83, 2.94 and 6.33 μm were produced by slip casting and pressureless sintering. They were used to turn medium carbon steel in dry, continuous cutting conditions, at a cutting speed of 450 m min -1. Examination of the flank face showed that the flank wear land was characterized by long and parallel ridges at short machining times, with the ridges becoming wavier as the grain size of the insert increased. The initial volume flank wear rate increased with increasing grain size of the insert and is consistent with grain spallation being the primary wear mechanism, although the wear rate was moderated by the subsequent smearing of spalled grains onto the tool surface by single glide. After the attainment of a critical width of flank wear land, a transition in wear feature to a two-zone wear feature with spikes nearer the cutting edge and ridges further away occurred; shortly after which the volume flank wear rate decreased appreciably. A similar two-zone wear feature was also observed on the crater of the tool even with short machining times. Although the size of the spikes observed in the crater varied with the grain size of the insert, crater wear rate, expressed as time rate of change of the maximum crater depth, is grain-size independent. This is because the maximum depth of the crater occurred in the region covered with spikes, where material loss is controlled by plastic deformation-induced necking of asperities, a process known to be grain-size independent.

A study on wear resistance of the white layer

The white layer has received some consideration, but there are two different opinions on its wear characteristics. It is considered to be of tribological advantage in some instances. However, the microcracks and voids formed by adiabatic shearing are precursors to fracture and should decrease the wear resistance. As to the white layer previously generated by impact wear, the wear characteristic of the white layer is studied by a pin on disc machine in the present paper. It is found that the white layer causes delamination of material, which increases the wear loss significantly. The delamination of the white layer, being prior to the cutting wear, is the primary wear mechanism for materials with the white layer.

Comparison of dry wear characteristics of two abrasion-resistant steels: Q/T C1095 and 15B37H

The dry reciprocating wear characteristics of two abrasion-resistant steels, C1095 and 15B37H, against an abrasive material were studied. Results showed that abrasive wear and surface fatigue were the primary wear mechanisms. The wear failure of the steels was related to frictional softening during wear.

Tribological behavior of TiC/TaC-reinforced cermet plasma sprayed coatings tested against sapphire

This paper deals with the investigation of the tribological behavior of TiC/TaC reinforced NiCrMo and Mo plasma sprayed coatings. The coatings were classified with respect to friction and wear behavior in pin-on-disk tests. The NiCrMo-based coatings, with better carbide-metal matrix binding than the Mo-based coatings, are also the more wear resistant. The NiCrMo-based coatings show a better functionality, when the reinforcing particles area solid solution of TiC and TaC, than the coatings with only TiC or TaC reinforcement. Abrasion, adhesion and fracture assisted wear were observed to be the primary wear mechanisms involved in these complex TiC/TaC reinforced coatings, as revealed by SEM investigation of the wear tracks and the debris. The extent of each mechanism appears to be influenced by the carbide-matrix interface strength. The processing to structure and functionality relationships highlight the key parameters in the effort to design high wear resistant coatings.

Thick Ti/TiN multilayered coatings for abrasive and erosive wear resistance

Abstract Plasma-assisted physical vapour deposition (PAPVD) of hard coatings such as TiN is widely employed on cutting and forming tools where a thin coating ( i.e. 1–5 μm) is sufficient to control the primary (usually “adhesive”) wear mechanism. Diversification into other application areas, such as components for which abrasive wear resistance is the main requirement, has however been constrained by coating thickness limitations (typically to below 10 μm)—due to debonding caused by the build-up of internal stresses. The hardness and “load-support” mismatch between such coatings and the more widely used metallic ( i.e. non-tool steel) substrate materials (both ferrous and non-ferrous) also leads to a requirement to modify coating-substrate interfacial properties and decouple substrate mechanical (and-to some extent-electrochemical) effects from the important coating surface or “near-surface” requirements. Here we report a technique for interlayering of TiN with titanium to produce a “toughened” composite coating which can be greater than 60 μm thick. By control of layer thickness and interfacial properties, the brittle-fracture failure regime normally associated with TiN on relatively soft substrates can be replaced with a ductile “tearing” mechanism which provides improved performance in three-body abrasive wear tests and airborne-particulate erosion simulation trials. The implications of multilayered and multitreatment coatings in widening the applicability of PAPVD treatments are also discussed.

Relation of friction and wear to processing parameters of polycrystalline diamond films grown on silicon and silicon and silica substrates by the hot filament method

Polycrystalline diamond films were deposited on silicon and silica substrates in a hot filament chemical vapor deposition reactor using venous pretreatment times and methane gas concentrations. Friction and wear tests were performed with a pin-on-disc tribometer under 100 and 200 gf loads without lubrication in the ambient environment. Tests show that friction coefficients decrease with both increasing load and number of traces, which was attributed to the formation of graphite during wear. Wear tests indicate graphitization to be the primary wear mechanism, with occasional wear pits caused by grain pull-out. The formation of wear pits is believed to be related to the presence of amorphous carbon in a very small fraction of the grain boundaries.

Analysis of the tribological behaviour and wear mechanisms of titanium nitride coating

Experiments were conducted on a test machine that used a thrust-washer adapter, where a rotating upper specimen was pressed against a stationary lower specimen. This setup was used to simulate the surface contacts between the steel (of the ring) and the titanium nitride coating (on the washer). Further, the existence of an electroless nickel interlayer on the washer was also investigated. The effect of the coating layers on tribological behaviour was evaluated for different thickness combinations of the titanium nitride layer (top layer) and the electroless nickel layer (interlayer). The interlayer was found to increase the wear volume, but was advantageous for strengthening resistance against chemical corrosion. The wear volume was controlled by the thickness of the two coating layers. A thicker TiN layer in conjunction with a thinner interlayer constituted the appropriate combination for two coating layers from the viewpoint of lowering wear volume. The friction coefficients arising from the TiN coating generally varied in the narrow range between 0.5 and 0.55, regardless of the interlayer thickness. Both the friction coefficient and wear volume were affected very much by the applied load and sliding speed. In the testing operating conditions, the primary wear mechanisms of the coating layers, such as microabrasion, semicircular or curved cracking, plucking and grooving, formed the surface failures. The surface failures due to friction and wear that occurred within the top layer appeared to be nearly independent of the adhesive strength of the interface.

Analysis of the friction and wear mechanisms of multilayered plasma-sprayed ceramic coatings

Wear tests were conducted on a rotor-vane-disk adaptor where three rotating vanes were pressed against a disk. Vanes were coated by WC and used as the upper specimen while the disk was coated by Cr 2O 3 and used as the lower specimen. A buffer layer of various thicknesses and contents was placed between the top coating and the bulk steel of the disk to alleviate the effects of the large difference in thermal properties of the two materials. The experimental results reveal that correct placement of a buffer layer can indeed improve the wear resistance. Factors such as the temperature to which the specimen was heated before testing, the proportion by weight of each individual constituent in the buffer layer, and the thickness of each coating layer, were also important for the volume of wear of the lower specimen. As the specimens were heated to higher temperatures, the wear volume decreased with increasing proportions of Cr 2O 3 in the buffer layer. Elevating the preheating temperature of the specimens can diminish the wear volume but increases the friction coefficient. The steady-state wear rate is not much influenced by the constituents of the buffer layer and the coating thickness. Brittle fracture, abrasion, adhesion and oxidation were found to be the primary wear mechanisms in the tests.

Wear with low-lubricity fuels I. Development of a wear mapping technique

Use of low-lubricity fuels such as Jet A-1 is now relatively common in military ground equipment, while severe refinery processes such as hydrotreating are removing reactive components from commercially available diesel fuels. Under critical conditions, durability problems with fuel-sensitive equipment emerge with the use of Jet A-1. Consequently, a bench wear test that accurately reflects the environment within the fuel injection system is needed. However, a better understanding of the primary wear mechanisms present in the fuel injection system and their relationship with potential bench wear tests is first required. Wear maps have previously been used to study ceramic materials and to define the wear mechanisms in metallic contacts. This technique systematically produces a data base according to a self-consistent methodology and allows the effects of each contact parameter to be precisely described. This paper, the first of two, details the initial test development required to ensure that the data base is completed according to a single well-defined procedure. The second paper, “Correlation between wear maps and pump components”, uses the test methodologies and results developed to elucidate the wear mechanisms present in fuel-lubricated contacts and to assist in bridging the gap between laboratory tests and practical applications.

Tribological Characteristics of α‐Alumina in High‐Temperature Water

The effects of temperature, sliding speed, and contact load on the tribological behavior of an α‐alumina ceramic sliding on the same material in water were investigated in the range from room temperature to 300°C under the corresponding saturated vapor pressures. The specific wear rate increased remarkably at elevated temperatures. The primary wear mechanisms in high‐temperature water are considered to be microfracture, promoted by the solution of grain boundary layers, and stress corrosion cracking. A film containing γ‐alumina particulates appeared on the worn surface with increasing sliding speed and increasing contact load in 300°C water.

Dry sliding wear behavior of an Si-Al-O-N ceramic

Dry sliding wear tests were conducted on (Si-Al-O-N)-cast iron sliding pairs using a wear tester specifically designed to simulate closely the high pressures, velocities and resultant temperatures encountered in heavily loaded machinery and other engineering applications. A wear tester was designed so that both the contact load level and the sliding velocity could be varied. Wear testing indicated that, following a short wear-in period, mass loss varied linearly with sliding distance for all contact loads and sliding velocities investigated. The steady state wear rates, expressed in terms of mass loss per unit sliding distance, were found to increase as the applied contact load was increased for all the sliding velocities investigated. Further, the wear rate was found to vary inversely with sliding velocity for the highest contact load level investigated. For the intermediate and lowest contact load levels, this inverse relationship between velocity and wear rate ( i.e. reduced wear for higher velocities) was less pronounced and restricted to the lower range of velocities investigated. Several different grinding procedures were used to prepare the specimens prior to wear testing but were found to have no significant influence on the measured wear rates. The experimental results are qualitatively explained by considering combined wear mechanisms involving brittle fracture and plastic deformation, which depend on the relative magnitudes of contact load and sliding velocity. Brittle fracture is assumed to be the primary wear mechanism especially at high contact loads and low sliding velocities. Plastic deformation mechanisms are also active and intensify with increasing frictional heating and concomitant thermal softening.

Examination of wear mechanisms in automotive camshafts

Two worn camshafts from a taxi fleet test were examined by scanning electron microscopy, energy-dispersive analysis by X-rays, Auger emission spectroscopy and secondary ion mass spectrometry. The cam lobes were selected to represent the extremes of cam wear. The two different lubricant formulations used in the engines differed in the VI improver, the dispersant, the antioxidant and the antiwear additive. This investigation showed that surface deformation and fatigue are the primary wear mechanisms on the cam lobe surfaces in the absence of catastrophic wear by scuffing. The fatigue pits were larger and more numerous on the cam lobe with the larger amount of wear. It was also found that lubricant additive components penetrate along the microcracks and the graphite flakes to a great depth. It is suggested that the penetrated lubricant components may cause accelerated fatigue crack growth by stress corrosion cracking.

Influence of oxygen on the wear of silicon

The results of a series of wear tests on semiconductor silicon chips are presented. In these tests, hemispherical anodized aluminum sliders rubbed against flat silicon specimens with a small-amplitude oscillatory motion. The influence of several parameters, including the load, the slider roughness, the type of anodization, the contact geometry, the environment and the initial condition of the silicon surface, on the wear of the silicon was studied. Of these the influences of the environment and the initial condition of the silicon surface were most pronounced. It was concluded that oxide formation and growth on the silicon were important factors in the wear of the silicon and tended to increase the wear. It was also concluded that the primary wear mechanism of the silicon for low load is probably delamination or surface fatigue.

Application of republic steel corporation’s simulated gear cutting test to the development of improved machining steels

Republic Steel Corporation utilizes a simulated gear cutting test (SGCT) in assessing the relative machinability of experimental and commercial steels. The test was originally designed to simulate hypoid gear cutting operations where the primary wear mechanism is through abrasion. To accomplish this end, low speeds and feeds which result in light chip loads are used. General and localized flank wear of the 12-bladed, precision ground milling cutter is monitored throughout the test. Wear rate performance bands as a function of metal removed have been established for several grades of gear steels produced by standard furnace practices. Modifications in furnace practice and the effects of alloying additions on machinability can be assessed by comparing their SGCT response to the base performance bands. Examples of the application of this test to alloy development programs are given. The simulated gear cutting test, when interpreted along with other machining tests employed at Republic Steel’s Research Center has proved to be a time-saving vehicle in alloy development efforts.

Primary modes and observable phenomena in the mechanical wear of metals

Four primary wear mechanisms are deducible from the behavior of moving surfaces in contact under load, (a) the adhesive mechanism; (b) the plastic deformation mechanism; (c) the spalling or pitting mechanism; (d) the chemical or corrosive mechanism. The recognition of the action of these mechanisms on examination of worn surfaces from well-controlled experiments with a pin and disk apparatus is described. The difficulty of identifying the determinative mechanism for destructive wear by inspection of badly damaged parts is discussed.