Effect of the severe plastic deformation and aging temperature on the strengthening,structure, and wear resistance of a beryllium bronze

The effect of the aging temperature, severe plastic deformation by equal-channel angular (ECA) pressing at 400°C, and subsequent aging on the rate of wear, friction coefficient, and microhardness of a commercial beryllium bronze Br.B2 quenched from 800°C has been investigated. The bronze structure before and after tribological tests has been studied with the help of metallographic and electron-microscopic methods of analysis. It has been shown that tempering (aging) of the bronze at 250–400°C for 3 h leading to a sharp growth of the hardness substantially increases the wear rate of the bronze in pair with the steel 45 under the conditions of both dry and boundary sliding friction. The cause of this is a decrease in the toughness of the surface layer of the bronze due to the precipitation of particles of the strengthening γ′ phase (CuBe) from the α solid solution. Severe plastic deformation (ECA pressing) markedly enhances the wear resistance of the bronze subjected to subsequent aging at 250–400°C. This is because ECA pressing favors the formation of an extremely dispersed nanocrystalline structure with α-phase crystals 40–50 nm in size at the wear surface of the bronze; whereas in the friction zone of the quenched bronze or the quenched and aged bronze, there arises a significantly less dispersed structure with matrix crystals to 300 nm in size. It has been assumed that under conditions of the rotational mechanism of plastic deformation operating upon sliding friction in the near-surface layer of the bronze, the increase in dispersity of its structure attained by using ECA pressing enhances the toughness and, correspondingly, wear resistance of the aged bronze.