Wear and friction of unio crassus shell in dry sliding contact with steel

Biological materials such as shells possess a useful combination of mechanical properties. For instance, good fracture toughness combined with a relatively high hardness has been reported. The response of these properties to a tribological performance could presumably be very beneficial. Unfortunately no such research has been reported, although this kind of information is invaluable in possible utilization of biomimetic or biological processes in producing of materials.

In this work chemical composition of Unio Crassus shells were characterized using secondary ion mass spectroscopy (SIMS) and Rutherford backscattering spectroscopy (RBS) and the microstructure was determined with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Specimens of 20×10 mm in size with a thickness of a few millimetres were cut and mechanically polished followed by ultrasonic cleaning in deionized water. Wear and friction measurements were performed in a pin-on-disc tester with a hardened steel pin 6 mm in diameter as a counter face. Tests were carried out in a relative humidity of 50% at room temperature with a sliding speed of 15 mm/s. The measurements indicate a friction coefficient of 0.3–0.4 which is reasonable low. Moreover, wear resistance was found to be excellent. The wear resistance of the material was similar to those of the best synthetic diamond-like carbon films. The storage of the specimen at room temperature for 150 days deteriorated the material resulting in much worse tribological properties.