Wear

The current study investigates the characteristics of particles generated from the wear of braking materials, and provides an applicable index for measuring and comparing wear particle emissions. A pin-on-disc tribometer equipped with particle measurement instruments was used. The number concentration, size, morphology, and mass concentration of generated particles were investigated and reported for particles 10 nm-32 m in diameter. The particles were also collected on filters and investigated using EDS and SEM. The effects of wear mechanisms on particle morphology and changes in particle concentration are discussed. A new index, the airborne wear particle emission rate (AWPER), is suggested that could be used in legislation to control non-exhaust emissions from transport modes, particularly rail transport.

A conventional scanning reference electrode technique (SRET) has been modified to provide a novel method for characterising the real-time localised tribocorrosion behaviour of uncoated and physical vapour deposition (PVD) coated samples. The modification was carried out based upon the principle of a ball-on-cylinder contact. Here a sliding probe, in this case a changeable alumina ball, is positioned diametrically opposite a pseudo (Pt) reference electrode probe which is positioned 100 m away from the surface of a cylindrical specimen which rotates at a set speed. The contact probe, specimen and reference probe are immersed within a chosen electrolyte, which for this study, is aqueous 0.01% NaCl. The dynamic corrosion activity is monitored via the Pt probe by recording variations in ionic flux emanating at the surface of the corroding sample. The SRET can operate in two modes, namely line scan, in which corrosion activity along the circumference of the specimen is measured, or map scan in which a 2D corrosion activity area map of the surface of the specimen is obtained. This paper presents the design, calibration procedures, and real-time tribocorrosion behaviour of uncoated and PVD (C/Cr) coated 316 stainless steel as a function of the contact load, and test conditions. Evidence of the effects of wear damage due to contact by the alumina ball was obtained by monitoring the SRET activity during loading (contact) and unloading conditions. The real-time local tribocorrosion activity can be detected immediately a load was applied. Such activity was found to stop, due to surface repassivation, upon removal of the load (alumina ball). The results show that the applied loads affect the free corrosion potential, local current density, active anodic areas and the sample recovery time of the tested samples. The wear tracks were investigated using optical and scanning electron microscopy and laser profilometer. Correlation of tribocorrosion damage and contact load has been investigated.

Total disc replacement emerged as an alternative to fusion for the treatment of degenerative disc disease. Optimization of the bearing surfaces is critical to mitigate wear-related biological reaction. The purpose of this study was to characterize the wear of the A-MAV TM metal-on-metal total disc replacement using a spine wear simulator, per the ASTM F2423-05 standard guide. Six specimens were tested under flexion-extension (FE) conditions for ten million cycles (MC), followed by lateral bending (LB) combined with axial rotation (AR) for an additional ten MC. A run-in wear period was observed during the first 0.5 MC for both testing conditions, followed by a steady-state wear rate of 0.33 ± 0.12 mm 3 /MC in FE and 0.43 ± 0.06 mm 3 /MC in combined motion. Phasing between LB and AR led to a crossing-path motion as observed on explanted devices. This study suggests that clinically-realistic surface morphology may be achieved by carefully selecting the wear test parameters specified in the ASTM standard guide. Furthermore, the use of metal-on-metal bearings in spinal arthroplasty may be viable in view of the low wear exhibited by this material combination.

This work presents the development of a method which analyzes metallic wear debris and contaminants found to be present in fuels used by Diesel engines. The particles have been isolated by following two complementary methods; firstly, a magnetic separation method and then a filtering method using membranes. Particles are subsequently characterized by means of optical and electron microscopy, where it is possible to establish the type and severity of the wear, as well as establishing how the mechanism parts are actually affected by wear. This technique allows a predictive maintenance of the fuel injection systems to be carried out, as it allows for possible breakdowns to be detected prior to a serious failure being produced.

The Al x CoCrCuFeNi alloys with different aluminum contents prepared by arc melting were investigated on their adhesive wear behaviors. With increasing aluminum content, both the volume fraction of BCC phase and the hardness value increase, and thus the wear coefficient decreases. Moreover, the wear mechanism changes from delamination wear to oxidative wear. For low aluminum content, x = 0.5, the microstructure is of simple ductile FCC phase and the worn surface is deeply grooved and undergoes a periodic delamination which produces big debris. For medium aluminum content, x = 1.0, the microstructure is a mixture of FCC and BCC phases, and the worn surface is deeply grooved in FCC region but smooth in BCC region. Delamination wear is still dominant although oxidative wear occurs in the smooth region. For high aluminum content, x = 2.0, the microstructure is of BCC phase and the worn surface is smooth and yields fine debris with high oxygen content. The high aluminum content gives a large improvement in wear resistance. This improvement is attributed to its high hardness, which not only resists plastic deformation and delamination, but also brings about the oxidative wear in which oxide film could assist the wear resistance.

In sheet metal stamping, it is known that wear is unevenly distributed over the die radius and that multiple wear mechanisms may occur simultaneously. However, there has been little or no work that details the types of wear mechanisms, and quantifies the locations at which they occur. Furthermore, the link between recently identified time-dependent contact conditions and the wear response is currently unknown. An experimental study is presented in this paper to examine the location, type and severity of wear that occurs over the die radius during a typical sheet metal stamping process. It is found that the wear over the die radius consists of a combination of ploughing and galling mechanisms. The relative severity of the ploughing mechanism is divided into two distinct zones on the die radius, which correlate well with the contact pressure and sliding distance behavior predicted in our recently published numerical study. The galling mechanism results in failure of the stamping process and is, therefore, critical to the overall tool wear response. Our analysis indicates that the severe contact pressure/small sliding distance conditions, which occur during the initial stage of the process, cause the galling behavior observed over the radius. Therefore, it is concluded that the overall tool wear response and tool life is primarily dependent on the initial transient stage of the stamping process.

When a steel ball undergoes dry sliding against a boron carbide-coated steel coupon, both the steel ball and the boron carbide are polished, even though the boron carbide is several times harder than the steel. We have measured the abrasion rate of the steel under loads ranging from 5 to 1100 g. The average abrasion rate at and above 100 g of load shows a simple power law dependence on the number of cycles, but a deviation from this simple dependence is observed at lower loads. The loss of abrasiveness of the boron carbide correlates with a reduction of the RMS angle on the boron carbide surface, which eventually becomes nearly atomically smooth over regions as large as 1 m × 1 m. Our results suggest that under the right conditions, a boron carbide coating could be designed to polish a counterpart gear or bearing surface with little risk that the counterpart would be substantially worn and with little concern for how the load varied during a break-in period. We suggest that polishing of the boron carbide surface by steel is a chemical process, while the abrasion of the steel by boron carbide is a mechanical process.

According to most studies dealing with wear, abrasion can be considered on one hand as micro-cutting, leading to material removal (grinding), and on the other hand as micro-ploughing, leading to plastic deformation and lower material removal (abrasive wear). Understanding various flowing transitions around an abrasive particle, under well-established conditions, makes it possible to better control these processes. The aim of the present study is to understand plastic deformation and failure local phenomena induced by an abrasive process. Experimental studies have been carried out on an abrasive process which consists in scratching a soft flat surface (AISI4140 steel) by mean of a turning tool fixed on the periphery of a disc. Regulating angular and feed speeds, successive scratches are expected to study phenomena generated by a single pass of the cutting tool. Scratch topography and forces are measured in order to highlight the influence of the depth of cut and the cutting speed on these parameters and on specific energy.