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The development and implementation of a wide range of innovative nanomechanical test techniques to solve tribological problems in surface engineered systems are described in this review. By combining results with several different nanomechanical techniques, predictive design rules based on the elastic and plastic deformation energies involved in contact are proposed to optimise mechanical properties in the various contact situations that occur for different applications. Results are presented with the NanoTest platform for applications in biomedical devices, surface engineering of lightweight alloys, wear resistance of physical vapour deposition and chemical vapour deposition coatings as well as fracture fatigue resistance of diamond-like carbon coatings. Surface engineering to increase the ratio of hardness to elastic modulus (H/E) can be beneficial in a range of applications but care should be taken that, first, it be done without introducing too large intrinsic stress or stress discontinuities in mechanical contact loading, second, the severity of the contact results in high stresses and there is a requirement for some plasticity in contact to avoid fracture.

Reliability of MEM (microelectromechanical) devices can be limited by stiction forces that develop in use. It is desirable to alter the mechanical and interfacial behaviour of the silicon surfaces by the application of very thin, low surface energy and low stress coatings. In this publication we report the nanomechanical and nanotribological characterization of a range of 5–150 nm thin films deposited on silicon by filtered cathodic vacuum arc (FCVA) and closed field unbalanced magnetron sputtering. A method of analysing nano-scratch data with spherical indenters is proposed. The method suggests the onset of non-elastic deformation in the nano-scratch test is due to substrate yield rather than film deformation on all but the softest films studied in this publication. The critical load for total film failure is a marked function of indenter radius, the ratio of hardness to modulus and the film thickness. The FCVA films were tested with probes of different radii (1.1, 3.1 and 9.0 µm) and the critical load for film failure was found to vary strongly with probe radius. The deposition of <100 nm amorphous carbon films on Si could be a promising strategy for improving the reliability of Si-based MEMS devices as none of the very thin films tested underwent stress-related delamination failures that occur behind the indenter during the nano-scratch testing of thicker amorphous carbon films.

A small scale probe testing method has been developed for investigating the behaviour of thin films under dynamic loading conditions. The primary objective of the development was to produce quantifiable techniques that closely simulate the conditions that thin films experience in service. Variations of the technique allow measurements related to: impact wear and adhesion failure, erosive wear resistance, fracture toughness, work hardening, and dynamic hardness. The common element in each variant is the acceleration of a test probe (usually diamond) towards the specimen surface and the monitoring its instantaneous position before and after collision. The impact energy can be controlled and either single impacts or multiple impacts can be produced. For single impacts, the energy delivered to the contact point can be quantified, allowing calculation of a dynamic hardness number.

Wear and stiction forces limit the reliability of Silicon-based micro-systems when mechanical contact occurs. Ultra-thin filtered cathodic vacuum arc (FCVA) ta-C films are being considered as protective overcoats for Si-based MEMS devices. Fretting, nano-scratch and nanoindentation of different thickness (5, 20 and 80 nm) ta-C films deposited on Si(100) has been performed using spherical indenters to investigate the role of film thickness, tangential loading, contact pressure and deformation mechanism in the different contact situations. The influence of the mechanical properties and phase transformation behaviour of the silicon substrate in determining the tribological performance (critical loads, damage mechanism) of 2 the ta-C film coated samples has been evaluated by comparison with previously published data on uncoated Silicon. The small scale fretting wear occurs at significantly lower contact pressure than is required for plastic deformation and phase transformation in nanoindentation and nano-scratch testing. There is a clear correlation between the fretting and nano-scratch test results despite the differences in contact pressure and failure mechanism in the two tests.In both cases increasing film thickness provides more load support and protection of the Si substrate. Thinner films offer significantly less protection, failing at lower load in the scratch test and more rapidly and/or at lower load in the fretting test.