A review of the performance of engineering materials under prevalent tribological and wear situations in South African industries

The wear of materials used on machinery operating in a wide range of industrial situations such as mining, energy production and agriculture can cause serious inefficiencies, sudden breakdowns and consequential financial losses. Our work over two decades has concerned industrial problems encountered in South African industry, and laboratory simulations of abrasion, abrasion plus corrosion, adhesive wear, impact wear, cavitation, solid particle erosion and erosion plus corrosion situations have been successfully undertaken. Materials investigated include plain carbon and alloy steel, stainless steels, aluminium alloys, cast irons, tungsten carbide cermets, ceramics, polymers, composites and various surface treated and coated materials. The paper reviews the investigations carried out in our laboratories and conclusions we have made.     

On the influence of surface finish of SSiC on the results of tribological laboratory tests in the case of water lubricated oscillating sliding

The development of materials for tribological applications requires characterisation of their friction and wear behaviour. This characterisation is often based on tribological model testing, working with simple shaped specimens, running under well-defined conditions. Discrepancies in test results may arise from the fact that non-standard tests with different sets of operational parameters are used. An essential starting point for the development of tribological standards is knowledge of the main parameters that influence the tribological properties. One aspect that is not often adequately taken into account is the surface finish of the test specimens. Results are presented of friction and wear tests with self-mated SSiC couples (ball on disc), running in water in an oscillating sliding mode. The surfaces of the disc were ground, lapped, or polished, respectively, running against a polished ball. For certain test conditions, the influence of the surface finish on wear is found to be negligible, while for other conditions, the wear rate can differ by one order of magnitude or even more. The consequences for the standardisation of wear tests of ceramic materials are discussed.     

Improvement in the tribological properties of imidazolium‐derived ionic liquids by additive technology

Molecular design of wear‐preventing and friction‐reducing additives for ionic liquids is described. The tribological properties of carboxylic acid‐derived additives were evaluated by a ball‐on‐flat type tribotest under reciprocating motion. Tetraalkylammonium and tetraalkylphosphonium salts of N‐benzyl‐protected aspartic acid were dissolved in 1‐alkyl‐3‐methylimidazolium‐derived ionic liquids. They prevented wear remarkably and reduced friction fairly. Influences of alkyl group in imidazolium molecule on additive response were observed. In tetraalkylammonium‐derived ionic liquids, the additive reduced wear but did not reduce friction under these conditions. The salt of N‐acetyl‐protected glutamic acid prevented wear, but did not reduce friction. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental study of the friction and wear behaviour of a polymer disc/primer coating combination used in ball‐joints by means of large‐scale testing

The surfaces of a heavily loaded ball‐joint were initially covered with a sliding spray, and suffer wear. A solution is found by incorporating ultra high molecular weight polyethylene (UHMWPE) discs with a carbon fibre/epoxy reinforced ring as sliding material into the chairs of the structure. The ball side is covered with a zinc phosphate primer coating. For design purposes the local static and dynamic behaviour of the hybrid UHMWPE discs in contact with steel or Zn‐coated counterfaces should be large‐scale tested in terms of their loading capacity, low friction and wear resistance. Also the influence of creep and wear on friction is examined. After the large‐scale verification tests in laboratory, a good correlation is found with a test in the field. Copyright © 2006 John Wiley & Sons, Ltd.