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a b s t r a c tProduction of wear debris has been linked to the failure of numerous hip implants. With the current focus on increasing the implant longevity, thus wear and corrosion resistance is important. Hard coatings have the potential to reduce the wear and corrosion. Diamond like Carbon (DLC) coatings exhibit properties that could make them viable for implants. This paper critically reviews previously published research into usage of DLC coatings for implants. Overall DLCs seem to be an effective coating for implants but with the variance in results, further testing is required for clarification of use.

The performance of man-made materials can be improved by exploring new structures inspired by the architecture of biological materials. Natural materials, such as nacre (mother-of-pearl), can have outstanding mechanical properties due to their complicated architecture and hierarchical structure at the nano-, micro- and meso-levels which have evolved over millions of years. This review describes the numerous experimental methods explored to date to produce composites with structures and mechanical properties similar to those of natural nacre. The materials produced have sizes ranging from nanometres to centimetres, processing times varying from a few minutes to several months and a different range of mechanical properties that render them suitable for various applications. For the first time, these techniques have been divided into those producing bulk materials, coatings and free-standing films. This is due to the fact that the material's application strongly depends on its dimensions and different results have been reported by applying the same technique to produce materials with different sizes. The limitations and capabilities of these methodologies have been also described.

a b s t r a c tErosion-corrosion is a complex phenomenon which involves the interaction between the mechanical processes of solid particle erosion and the electrochemical processes of corrosion. A whole range of issues is faced by a designer when trying to obtain relevant information on erosion-corrosion performance of a material. Amongst the constraints are the dispersed test conditions and test rigs available in the literature making comparisons and quantifying erosion-corrosion wear rates of different materials very difficult. The aim of this work is to evaluate the repeatability of erosion-corrosion experiments and to investigate the role of different parameters influencing erosion-corrosion. The materials tested in this work are stainless steel (SS316L/UNS S31603), carbon steel (AISI 1020/UNS G10200) and nickel-aluminium bronze (NAB/UNS C63200). A slurry pot erosion tester was used as the test apparatus and test parameters such as erodent size, erodent concentration, flow velocity and test solutions were varied to study their effect on erosion-corrosion. SEM analysis showed that a similar erosion-corrosion mechanism is seen for SS316L and NAB with formation of multiple extruded lips and platelets typically seen for erosion dominated material. In contrast the surface of AISI 1020 revealed the formation of craters, pits and shallow indentations which suggests that corrosion mechanism has a dominant influence on the material. Error rates in tests were found to have an average of 5.5% which are relatively low indicating good repeatability of test measurements and data from the test rig. The erosion-corrosion resistance of AISI 1020, SS316L and NAB were compared and it was found that SS316L showed the lowest erosion-corrosion mass loss rates in all test conditions followed by NAB and then AISI 1020. However in terms of synergistic ranking, NAB showed the best resistance to the combined action of erosion and corrosion with the highest negative synergy value. Positive synergy was evident for AISI 1020 in 3.5% NaCl and SS316L in 0.3 M HCl. A wear map is presented to evaluate erosion-corrosion trends of the materials. This work combines the assessment of test repeatability, variation in test conditions and comparison of material performance which are key stages in a material selection process.

Research and development work at the University of Southampton using an electrostatic condition monitoring system developed by Smiths Aerospace Information Systems has shown that electrostatic charge signals can be used to detect the onset of wear in lubricated tribo-contacts. Preliminary investigations have already demonstrated the viability of this system when tested on a laboratory-based pin-on-disc rig, a reciprocating laboratory wear rig and in an FZG gear scuffing rig. These preliminary experiments have indicated several charging mechanisms may be involved, namely-tribo-charging, localised surface charge variations, exo-emissions and debris generation.The electrostatic monitoring system has now been implemented on a taper-roller bearing test rig. The electrostatic system employed comprises three wear-site sensors (WSS) and an oil-line sensor (OLS). The WSS are mounted close to the bearing in order to monitor the earliest stages of component surface breakdown and wear, whereas the OLS is placed in the re-circulation oil-line to monitor debris generated and transported from the deteriorating component. For the present tests, taper-roller bearing wear was monitored using electrostatic sensors as well as vibration and lubricant temperature measurements; also two additional oil-line monitoring devices, supplied by Macom Technology Ltd., using Eddy current technology and ferromagnetism to sense debris entrained in the lubricant recirculating system were employed.The experimental data shows that the electrostatic monitoring systems detected bearing deterioration up to 4 h prior to complete failure (seizure) during a seeded fault test. The electrostatic wear-site and oil-line sensors detected changes in charge that coincided with increases in vibration, temperature and debris generation detected by the two Macom units.