A. Ball

Cavitation erosion of stainless steels

Abstract The cavitation erosion resistances of two martensitic, two austenitic and three ferritic stainless steels were evaluated. An austenitic manganese steel was also investigated for comparison with the austenitic stainless steels. The martensitic steels have the highest erosion resistances followed by the austenitic stainless and manganese steels while the ferritic stainless steels have very poor cavitation erosion resistances. The mechanisms of resistance and modes of erosion were investigated by means of optical microscopy, scanning and transmission electron microscopy and X-ray diffractometry. This study has highlighted the importance of microstructure in controlling the cavitation erosion resistance of alloys.

The erosion of four materials using seven erodents: towards an understanding

Abstract In order that an overview of the erosion process be obtained, solid particle erosion tests on four materials have been performed using seven different erodents within a range of particle diameters D (63 to 1000 μm), velocities V (33 m s −1 to 99 m s −1 ) and impact angles α (30° to 90°). The materials are glass, alumina, WC–7% Co and 304 stainless steel. Seven erodents are steel shot, glass beads, silica, alumina, tungsten carbide, silicon carbide and diamond particles. Systematic studies of the influence of the impact variables on the erosion rate have been made. Scanning electron microscopy of the eroded surface and the erodents after impact has been performed. Empirical correlations between erosion rate and the parameters of erodents are obtained and discussed in terms of the modes and mechanisms of erosion. An analysis of these results reveals that for brittle materials, glass and alumina, the erosion rate is determined by kinetic energy, particle size and the relative hardness and toughness of erodents. However, for ductile materials, the shape and kinetic energy of erodents are the most important factors determining the erosion rate. There is no significant effect of hardness and toughness of erodents on erosion. An attempt to rationalise the results in terms of mechanisms has been made.

On the importance of work hardening in the design of wear-resistant materials

Abstract By considering abrasive and erosive wear as a consequence of a series of impacting strikes within a given stress range, it is possible to demonstrate the advantage of materials with high work-hardening rates.

Cavitation erosion of cobalt-based Stellite® alloys, cemented carbides and surface-treated low alloy steels☆

Abstract A number of Stellite ® alloys, cemented carbides and surface-treated alloy steels have been evaluated for erosion resistance. The ability of the Stellite alloys to withstand erosion is primarily a function of the cobalt-rich solid solution phase while erosion of cemented carbides is controlled predominantly by the binder phase. The nickel-based tungsten carbides are more resistant to erosion than the cobalt-based samples. Investigation of industrial surface treatments has demonstrated that erosion rates of hardened low alloy steels can be improved. For example, a hardened electroless nickel coating on BS 817M40 steel erodes at one-third the rate of uncoated BS 817M40 steel. A Tufftriding treatment, which is a proprietary method of carbonitriding, applied to the same steel caused a similar improvement in performance but only after an initial loss of the compound layer. Hard chrome coating is, in general, less effective than the above treatments in combating cavitation erosion.

Dry sliding wear of particulate-reinforced aluminium alloys against automobile friction materials

Abstract Two magnesium/silicon aluminium alloys each reinforced with 20 vol.% SiC particulates have been worn against three makes of automobile friction linings (brake pads). Two of the friction linings are commonly used against cast iron rotors in automobile braking systems while the third has been specifically formulated for use against aluminium metal matrix composite (MMC) brake rotors. Wear processes at the interfaces of the specific rotor-pad combinations have been characterised through the analysis of friction traces and the use of electron microscopy. For aluminium MMCs sliding against organic pads formulated for use against cast iron, wear rates are low and friction traces constant due to the formation of a solid lubricant graphitic layer at the wear interface. When these MMCs are worn against semi-metallic pads formulated for use against cast iron, wear rates are extremely high due to three body abrasion which leads to subsurface delamination and early melt wear in the MMC. For an aluminium MMC developed for its use in automobile brake rotors sliding against a semi-metallic pad specifically formulated for its use against MMC brake rotors, wear rates at low loads are low although friction traces are highly irregular and fracture of the SiC particulates occurs at the lowest load and sliding velocity. This fracture of SiC is induced by the abrasive action of hard alumina particles within the pad. At high loads and sliding velocities cohesiveness of materials within the pad is poor and the wear rate of the MMC is extremely high. If the structure and composition of friction linings are arranged correctly, the wear resistance and frictional properties of aluminium MMC brake rotors are superior to those of cast iron brake rotors.

On the synergistic effects of abrasion and corrosion during wear

Abstract The interactive effects of abrasion and corrosion were studied as a function of abrasive load, corrosion time and the frequency of abrasive and corrosive treatments. The initial rate of corrosion is independent of abrasive load but the percentage contribution to wear of corrosion decreases with increasing abrasive load. It has also been found that increasing the frequency of exposure to abrasion and corrosion increases the wear loss for a constant total amount of abrasion and corrosion. These effects are discussed in terms of the nature of the work-hardened surface layer and the chemical activity of this layer.

The abrasive-corrosive wear of stainless steels☆

Abstract Laboratory abrasive and abrasive-corrosive testing has been carried out on a range of ferritic, austenitic and martensitic stainless steels and the results compared with the testing of similar materials in situ in the abrasivecorrosive conditions of a gold mine. All grades were found to have better abrasive-corrosive resistance than proprietary abrasion-resistant alloys. The austenitic grades derive their outstanding properties from their capacity to resist unstable fracture of microshear lips on the abraded surface. This is due to the strain capacity afforded by the mechanical inducement of the martensitic phase transformations and the high work-hardening characteristics of the transformation product. The influence of this transformation has been studied as a function of prior cold work and velocity of abrasion on a range of austenitic grades of stainless steels. Notwithstanding these advantages of the austenitic grades, the ferritic grades are superior in terms of cost per unit volume lost and the new duplex ferritic-martensitic steel designated 3CR12 has potential as an abrasionresisting material in corrosive environments.

The wear of diamonds in impregnated diamond bit drilling

Abstract The wear of diamonds in impregnated diamond microbits was investigated in the laboratory by drilling a variety of rock types. The wear was studied by optical and scanning electron microscopy after drilling under a range of bit pressures, rates of advance, and rotational velocities using bits of different diamond size and concentration. The nature of the diamond wear modes did not vary with the drilling conditions but the relative proportions of different types of diamond wear changed with drilling performance. For stable drilling in any given rock type a characteristic threshold pressure existed above which desirable microfracture of the exposed diamonds was promoted over undesirable wear flat generation. The flats are produced by a sliding wear mode with the silicate minerals ploughing plastic grooves in the heated surfaces of the diamonds. Microfracture mode is the result of progressive growth and coalescence of cleavage microcracks promoted by the cyclical stresses experienced by the diamonds at pressures sufficient to cause indentation of the rock.

The effect of grinding direction on the nature of the transfer film formed during the sliding wear of ultrahigh molecular weight polyethylene against stainless steel

Abstract A study has been made concerning the nature of the transfer film formed during the reciprocating sliding wear of ultrahigh molecular weight polyethylene (UHMWPE) against a hardened stainless steel counterface under water lubrication. A range of UHMWPE has been subjected to water-lubricated, reciprocating sliding wear under a pressure of 10 MPa at a frequency of 2.5 cycles s −1 and an average speed of 0.25 m s −1 . It has been found that the interfacial deformation mechanism involves shear of thin surface layers of polymer and that the transfer film on the steel counterface is essentially multilayered. The worn polymer surfaces and debris have been extensively characterized for structural changes using X-ray diffraction and differential scanning calorimetry. It has been found that the wear debris is significantly more crystalline than the bulk polymer. The crystallinity of the wear particles is believed to be similar to that of the transfer film. No coherent transfer film was found when sliding was conducted parallel to the grinding direction on the steel surface. Polymer transfer was patchy, the amount increasing as the sliding distance increased. The debris was also found to be less crystalline than debris formed when sliding was conducted perpendicular to the counterface. An increase in molecular weight did not significantly improve the wear resistance. Small variations in counterface roughness values ( R a ) were found to have a much greater effect on the wear rates than changes in molecular weight. The steady-state wear rate of the polymer was furthermore found to be more dependent on an adherent transfer film rather than a change in bulk morphology.

Particle erosion of candidate materials for hydraulic valves

Abstract A range of metals and hard materials has been tested in an apparatus which simulates the unloader valve of a water-based hydraulic system. The water had been specifically contaminated with a low concentration of fine quartzite particles. The performances and modes of erosion for selected metals, ceramics and cermets are described.