Fracture of silicon-rich particles during sliding contact of Al–Si alloys

Fracture of silicon-rich particles (SRP) in a eutectic Al-12% Si alloy during sliding contact by a pyramid indenter was analyzed. The surface of the alloy was subjected to a chemical etching treatment (10% NaOH solution for 420 s) that maximized its wear resistance. SRP were observed to fracture from their roots – the point where the particle's protruded part met the etched aluminum matrix – when the ratio of SRP thickness (t) to the contact width of the indenter (W) was less than 1/8 under a normal load of 0.1 N. For large t/W ratios, particles were resistant to root fracture and exhibited evidence for plastic deformation on their contact surface. The critical particle thickness – below which particle fracture occurred – was shown to depend on the coefficient of friction of the alloy, its matrix hardness and particle fracture toughness. A model for estimating the optimum etching conditions for different SRP morphologies has been developed.