Modelling friction and wear of scratching ceramic particle-reinforced metal composites

The friction and wear behaviour of 6061 aluminium matrix composites reinforced with SiC and Al₂O₃ particles has been investigated at relatively high loads and speeds on a conventional scratch machine using a pyramidal indenter. It is identified that ploughing, adhesion and particle fracture all contribute to the friction and wear. The friction coefficient increases with particle volume fraction but is independent of the range of normal loads (1-20 N) and sliding speeds (1-10 mm s^{- 1}) tested. The wear volume generally increases with normal load and sliding distance (or pass number), and decreases with increasing particle volume fraction. A comparison of the measured scratch hardness and Vickers hardness shows that the former is not simply proportional to the latter for composites reinforced with large particles. A new friction and wear model is then established based on the theories of adhesion and ploughing and the effect of particle fracture. The validity of the model is confirmed by experiments and microscopic observations on the scratch topography of the metal matrix composites.