Metal surfaces properties Wear

Metal finishing is the name given to a range of processes carried out to modify the surface properties of a metal, for example by the deposition of a layer of another metal or a polymer, or by formation of an oxide film. The origins of the industry lay in the desire to enhance the value of metal articles by improving their appearance, but in modern times the importance of metal finishing for purely decorative reasons has decreased. The trend is now towards surface treatments which will impart corrosion resistance or particular physical or mechanical properties to the surface (e.g. conductivity, heat or wear resistance, lubrication or solderability) and hence to make possible the use of cheaper substrate metals or plastics covered to give them essential metallic surface properties. 

The hydraulic oil must provide adequate lubrication in the diverse operating conditions associated with the components of the various systems. It must function over an extended temperature range and sometimes under boundary conditions. It will be expected to provide a long, trouble-free service life its chemical stability must therefore be high. Its wear-resisting properties must be capable of handling the high loads in hydraulic pumps. Additionally, the oil must protect metal surfaces from corrosion and it must both resist emulsification and rapidly release entrained air that, on circulation, would produce foam. 

The recovery of petroleum from sandstone and the release of kerogen from oil shale and tar sands both depend strongly on the microstmcture and surface properties of these porous media. The interfacial properties of complex liquid agents—mixtures of polymers and surfactants—are critical to viscosity control in tertiary oil recovery and to the comminution of minerals and coal. The corrosion and wear of mechanical parts are influenced by the composition and stmcture of metal surfaces, as well as by the interaction of lubricants with these surfaces. Microstmcture and surface properties are vitally important to both the performance of electrodes in electrochemical processes and the effectiveness of catalysts. Advances in synthetic chemistry are opening the door to the design of zeolites and layered compounds with tightly specified properties to provide the desired catalytic activity and separation selectivity. 

UHMWPE possesses a unique combination of mechanical and technological properties and enjoys a variety of special applications based on low friction (solid lubricant), wear resistance (protection of metal surfaces), excellent chemical stability, as well as radiation and neutron resistance. UHMWPE is used in chemical processing, food and beverage industries, foundries, the lumber industry the electrical industry, as medical implants and in mining and mineral processing sewage treatment, and transportation. 

A combination of ZDDP and hard-core RMs leads to a synergistic effect of metallic detergents on the degradation of ZDDP. These phenomena are observed in many tests and can be explained in terms of (a) the acid neutralization property of hard-core RMs that leads to the prevention of decomposition of ZDDP (in the valve train wear test and the thin film oxygen uptake test), (b) the competitive adsorption of detergents that reduce the effective concentration of ZDDP on the metal surface (in the four-ball test), (c) the formation of mixed films on the metal surface, formed through the decomposition of ZDDP in the presence of hard-core RM s (the coefficient of friction in the Falex wear test). 

Table 5.3. The adhesive wear (mild wear, more severe wear, very severe wear) properties and tribofilm formation on metal surfaces (Hsu et al. 1997)...

A Japanese patent describes the treatment of metal surfaces with amorphous layers of second metals having a thickness of 0.2-2.5 pm. The metal component includes one, or more, of the following V, Nb, Ta, N, P, As, Sb, Bi, Cr, Mo, W, S, Se, Te, and Po. The introdnction of snch a snrface coating is claimed to improve wear and burning resistance of the metal. Also, the coating serves to increase the retention of oil films by the metal surface thus improving lubrication properties. 

Insertion of impurities Superconductivity of bombarded metals Variations of thin film properties Wear, friction and lubrication of materials Wear, friction and lubrication of materials Chemical state of implanted atoms Reactivity of ion-bombarded surfaces Reactivity of ion-bombarded surfaces Ionization phenomena Charge exchange studies... 

Lubricity Ester groups are polar and therefore affect the efficiency of anti-wear additives. When a base fluid is used which is too polar, it and not the anti-wear additives will be adsorbed onto, and cover, the metal surfaces, giving higher wear characteristics. Consequently, although esters have superior lubricity properties compared to mineral oil, they are less efficient than anti-wear additives. Esters are classified in terms of polarity or non-polarity by the van der Waal formula [48], Equation (2.1) ... 

Some additives used as anti-wear agents can also have anti-corrosion properties such as TCP, sebacic acid and azelaic acid. However, corrosion inhibition is a fine balance of competition with the anti-wear/load-carrying capability of the lubricant. Like the anti-wear additive, the corrosion inhibitor is designed to react with the metal surface. Some corrosion inhibitors specifically aimed at preventing static water corrosion of ferrous metals compete with the anti-wear additive for the metal surface to the extent that the resulting lubricant has poorer anti-wear properties than non-corrosion-inhibited lubricants. 

Chemists play a role in the addition of additives to improve the properties of motor oil. As steel and aluminum parts move closely against one another, friction between the two parts creates heat and wears away the metallic surfaces. This will lead to decreased efficiency, increased fuel consumption, decreased power output, and eventually engine failure. Engine additives are devised to combat these consequences. A list of engine additives follows however, rather than discussing each one in depth, we will discuss only some of the more important ones ... 

Lubricating oil is used to reduce friction and wear between bearing metallic surfaces that are moving with respect to each other by separating the metallic surface with a thin film of the oil. Petroleum derived lubricating oil is a mixture produced by distillation of selected paraffinic and naphthenic crude oils, after which chemical changes may be required to produce the desired properties in the product. The production of lubricating oils is well established and consists of four basic procedures ... 

Although atomic-scale studies of friction have not been carried out until recently—because of the lack of techniques such as the AFM—several mechanisms for friction and slide that depend on the physical and chemical properties of the materials in contact have been suggested. For example, friction and wear of metal surfaces are the highest for ductile materials. This can be understood in terms of the plastic flow that occurs at the interface for these materials under normal loads. With this plastic flow, adhesion proportional to the load also occurs, leading to increased friction and wear. In addition, the oxidation of a metal at the interface can also affect the degree of the friction. If the oxide of a metal has a higher hardness value than the metal itself, measured friction coefficients will be lowered upon oxidation. If,... 

Wear and frictional properties - The ability of the plastic to resist removal of material when run against a mating metal surface. The lower the frictional values, the better the relative rating... 

Friction coefficients, being not a physical property in the strict sense, but depending on the contact partners and many other external parameters, will be reported in the next section. The combination of low friction coefficients, typically < 0.2, with mechanical and surface properties which are partly polymer-like (elasticity, surface energy) and partly ceramic- or metal-like (hardness. Young modulus) qualitatively explains the outstanding position of DLC films as low-friction, highly wear-resistant coatings on which most of their present applications are based [77]. 

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