Tribological behaviour of anodised alumina nanohoneycombs

Abstract

Anodic alumina nanohoneycombs (AAO) have been widely used because of its convenient fabrication and controllable pores’ geometry. A lot of investigations have been conducted to study its physical and chemical properties. However, the mechanical properties, especially tribological properties, of such a popular nanomaterial still remain almost unknown. In this project, a series of scratch experiments were conducted on AAO films fabricated by a two-step anodisation method. The testing system is a G200 Nanoindenter provided by Agilent Corporation. A standard diamond Berkovich tip is used as the scratch tip. A scanning electron microscope was used to image the microstructure of the material deformation after scratching. Strengths of AAO domains with different pore regularities were compared by performing the scratch tests at constant normal loads crossing the boundaries separating these domains. Ramping load tests were carried out to show the effects of the normal load on the deformation and friction of the AAO. Scratch cycles and velocities were also varied to see their influence on friction and wear. The results show that the more ordered AAO structure has higher strength than disordered counterparts under scratch testing. The friction coefficient reduces rapidly on increasing normal load, and an explanation of this unusual behaviour is offered by considering the row-by-row deformation of the AAO structure. In multicycle scratch tests, the friction reaches a maximum at the fourth cycle. A step-like deformation behaviour was observed when the scratch velocity became extremely large, and this is probably due to the dynamic response of the instrument.