Properties abrasive wear

A schematic of electroplating system is shown in Figure 6.2. Electroplating is primarily used for deposition of material of desired properties (abrasion, wear resistance, corrosion protection, lubricity, and aesthetic qualities) to a surface that otherwise lacks that property. 

In addition to chemical analysis a number of physical and mechanical properties are employed to determine cemented carbide quaUty. Standard test methods employed by the iadustry for abrasive wear resistance, apparent grain size, apparent porosity, coercive force, compressive strength, density, fracture toughness, hardness, linear thermal expansion, magnetic permeabiUty, microstmcture, Poisson s ratio, transverse mpture strength, and Young s modulus are set forth by ASTM/ANSI and the ISO. 

Wear. Ceramics generally exhibit excellent wear properties. Wear is deterrnined by a ceramic s friction and adhesion behavior, and occurs by two mechanisms adhesive wear and abrasive wear (43). Adhesive wear occurs when interfacial adhesion produces a localized Kj when the body on one side of the interface is moved relative to the other. If the strength of either of the materials is lower than the interfacial shear strength, fracture occurs. Lubricants (see Lubricants and lubrication) minimize adhesion between adj acent surfaces by providing an interlayer that shears easily. Abrasive wear occurs when one material is softer than the other. Particles originating in the harder material are introduced into the interface between the two materials and plow into and remove material from the softer material (52). Hard particles from extrinsic sources can also cause abrasive wear, and wear may occur in both of the materials depending on the hardness of the particle. 

The main differences in the SteUite aUoy grades of the 1990s versus those of the 1930s are carbon and tungsten contents, and hence the amount and type of carbide formation in the microstmcture during solidification. Carbon content influences hardness, ductUity, and resistance to abrasive wear. Tungsten also plays an important role in these properties. 

Abrasion Resistance. Porcelain enamel is the most scratch resistant and hardest of commercial coatings (see Hardness). This property is used to distinguish between porcelain enamel and organic enamel or painted coatings. The rate of abrasive wear in surface abrasion increases with time, and the subsurface abrasion which follows exhibits a higher, but constant rate of wear. Abrasion resistance can be evaluated by loss of gloss or weight (35). 

Each mechanism of breakage implies a different functional dependence of breakage rate on material properties. For the case of abrasive wear of ceramics due to surface scratching by loaded indentors, Evans Wilshaw [Acta Metallurgica, 24, 939 (1976)] determined a volumetric wear rate V of... 

Titanium Carbonitride. Ti(C,N) is a solid solution of TiC and TiN and combines the properties of both materials. It offers excellent protection against abrasive wear and has good lubricating characteristics. It is used to coat tools and dies for the processing of ceramics, graphite, and filled plastics. 

PEN him is like PET film, but superior in various properties, and is finding wide applicahon for magnehc tapes. Weick and Bhushan have compared the dynamic mechanical properties and wear/abrasion properties of PEN- and PET-based magnehc tapes. The PEN tapes have better dimensional stability, elastic moduli and coating thickness. They also have higher storage moduli... 

A property not listed in Table 5.14, but which is of paramount importance to this application, is wear rate. Wear rate was described briefly in Section 8.2.2, and those concepts apply here as well. As it applies to tooth enamel, abrasive wear occurs by fracture or chipping of the enamel, chemical erosion, which may arise due to acidic medications or drinks, dietary oxalate, or high oral hydrogen ion concentrations as a result of disease, physical erosion, or abrasion, which arises due to idiopathic mechanisms, dentrifices, toothbrushes, or abrasive diets. For example, the wear rate of enamel has been measured at about 10 ttm/hour due to brushing with a toothbrush and toothpaste for 86,400 strokes [7],... 

The combination of properties discussed above makes the transition metal carbides, nitrides, and their solid solutions ideal materials for applications requiring rigidity and resistance to deformation, abrasive wear, and corrosion. 

The essential material property of rubbers is their low elastic modulus, which ensures that the contact deformation remains elastic over a very wide range of contact conditions. The abrasive wear of rubbers is due to either fatigue of the material or tearing by a cutting force from impacts with sharp-edged particles. 

For sliding abrasive resistance, the tough polyesters are the best suited. This also must be balanced against the hardness of the material. The older style PPG materials do not have the physical properties to provide outstanding resistance to abrasive wear. 

As in the case of corrosion failures, the sequence of steps involved in analyzing wear failures are initial examination of the failed component including service conditions to establish the mode or combination of modes of wear failure, metallographic examination to check if the microstructure of the worn part met the specification, both in the base material and in the hardened case or applied surface coatings, existence of localized phase transformations, shear or cold worked surfaces, macroscopic and microscopic hardness testing to determine the proper heat treatment, X-ray and electron diffraction analysis to determine the composition of abrasives, wear debris, surface elements and microstructural features such as retained austenite, chemical analysis of wear debris surface films and physical properties such as viscosity and infrared spectral determination of the integrity of lubricants and abrasive characteristics of soils or minerals in the cases of wear failures of tillage tools. 

Exposure to the environment (gases and humidity) affects mechanical properties, friction, and wear of polymers. Most of the time, synergistic effects between abrasion, wear and corrosion are created and that amplifies the damage.74,75 Dunn76 has summarized the dominant and synergistic influence of every factor as follows. 

Particle size is important and, for some applications requiring good weathering and impact performance (window profile), the ultrafine milled, high whiteness, natural version is normally used. To ease dispersion, the filler is usually coated with stearic acid. Coated ultrafine and precipitated calcium carbonates are claimed also to have a positive effect on impact properties in impact modified formulations (52, 294, 462). The abrasive wear of calcium carbonate, on melt processing equipment, is not significant but increases with increasing levels (177). 

The relevance of bulk fracture properties has therefore been considered essentially within the context of cohesive wear modes such as abrasive and fatigue wear. During abrasive wear, the initial stage is considered to be the process of contact and scratch between the polymer surface and a sharp asperity. The accumulation of the associated microscopic failure events eventually generates wear particles and gives rise to weight loss. Early approaches initiated by Ratner and co-workers [15] and Lancaster [16] attempted to correlate the abrasive wear rate with some estimate of the work to failure of the... 

Femoral ball heads of hip endoprostheses made from bioinert ceramics such as alumina or zirconia have to sustain high mechanical stresses, resorp-tion/corrosion by aggressive body fluid and abrasive wear over the lifetime of the implant in the human body of 15-20years. Some important properties of ceramic femoral ball heads are listed in Table 2.3 (Willmann, 1995). Mechanical properties of alumina and zirconia are discussed in Chapter 4.1. 

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