Automotive
Recent automotive development has concentrated on the optimisation of thin films and coatings used in a range of automotive applications, for example hard PVD coatings for coating piston rings, valve stems, bearings, gears. Also of interest is the scratch resistance of paints and clearcoats, brake pads and the fatigue wear of gears.
Many of the automobile components in question (engine components, brake pads) experience high temperatures during operation. With the NanoTest hot stage it is possible to optimize the mechanical and tribological properties of coated components at their operating temperature.
Case Study: Optimisation of DLC coatings for Automotive Use
DLC Applications in the automotive industry include Wrist pins, Spur gears, Plungers of injector pumps, Pistons, Valve train, Camshafts, Injector needles and more.
DLC films are finding increasing use as they have many excellent mechanical properties, such as they are inert, can be used at operating temperatures up to 350 C, have high hardness and low friction, and experience very low levels of wear under some conditions.
However there are also some drawbacks, including the fact that DLC suffers from brittleness, high stress, poor adhesion, poor resistance to fatigue, and is often limited in its thickness due to stress build-up in thicker layers.
In the example below, the influence of applied load on time-to-fracture and failure mode was investigated for a DLC-coated engine component. At or below 5 mN cohesive fracture occurs but at higher load there is a more damaging failure mechanism. Fracture over 5 mN is accompanied by coating delamination exposing the softer substrate.
The problems highlighted in the nano-impact test are mirrored in longer engine trials. To avoid them graded DLC coatings have now been developed and the nano-impact test is an important tool in the optimisation of their properties.
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| No fracture at this load within 900 s |
Fracture at this load within 600 s |
Fracture at this load within 30 s |
Tests can be repeated at loads up to 500mN with the NanoTest pendulum, or at much higher loads with the MicroTest pendulum to reproduce the contact pressure for different applications. Impact testing can be done with either loading heads up to a temperature of 500 C or more.
Customer Case Study: The University of Birmingham, UK
Weight saving is an important driver in high performance engines. For example, the valves in IC engines are usually made of steel. Advanced applications require lower inertial mass and light non-ferrous alloys have been suggested for engine blocks. Despite the weight saving, these materials can exhibit poor tribological properties. Researchers at Birmingham University used the NanoTest to study how the mechanical and tribological properties of FeAl and TiAl intermetallics vary with temperature, and how their load support and performance in tribo-contact can be enhanced by thermal treatment. Development of low friction and oxidation-resistant coatings for these lightweight materials is a natural progression.
Further Reading
Nanoindentation and nanoscratch of a thermal oxide layer on a FeAl alloy, T Bell et al, J Mater Res 19 (2004) 291.
Evaluation of the fracture resistance of DLC coatings on tool steel under dynamic loading BD Beake, Surf Coat Technol 198 (2005) 90.
Nano-impact testing - an effective tool for assessing the resistance of advanced wear-resistant coatings to fatigue failure and delamination, BD Beake and JF Smith, Surf Coat Technol 188-189C (2004) 594.
Mechanical and electrical properties of stainless steel sandwich sheets with fibrous metal cores, designed for automotive applications, AE Markaki, TW Clyne, "Metal and Ceramic Composites: Automotive Applications", Oxford-Kobe Materials Seminar, B Cantor (ed), IoP Publishing Ltd 2003
