Microstructural development in spray formed Al-3.5Cu-10Si-20Pb alloy and its comparative wear behaviour in different environmental conditions

摘要

The wear behaviour of spray formed Al-3.5Cu-10Si-20Pb (wt.%) alloy has been studied in different environmental conditions. The wear tests were carried out in air atmosphere and vacuum, using a pin-on-disc type wear testing equipment. The wear behaviour in air atmosphere clearly indicated the influence of surface oxidation on the mating surfaces. This resulted in the formation of irregular shaped oxide particles having bright contrast in SEM investigation of worn surfaces and debris particles. The nature of variation in wear with sliding distance, both in air atmosphere and vacuum, remained similar showing two distinct wear regimes, viz., running in wear and steady state wear. A relatively lower running in period and a large reduction in the frictional force were observed in vacuum as compared to that obtained in air under same conditions of sliding speed and applied pressure. The wear rate varied from (0.25 to 0.61) x 10~(-12)m~3 m~(-1) for a range of applied pressure of 0.2-1.8 MPa and at a constant sliding speed of 1.0ms~(-1) in vacuum, whereas, the wear rates observed in air atmosphere for the same sliding conditions range between (0.75 and 3.87) x 10~(-12) m~3 m~(-1). The coefficient of friction in air atmosphere varied for low pressures and remained almost constant at 0.25 in high pressure regime, whereas in vacuum it decreased linearly and finally attained a constant value of 0.1. The wear rates for different sliding speeds of 0.5-2.0 ms~(-1) at constant applied pressure of 1.0 MPa were compared. The results depicted two different regimes of variation in wear rate with sliding speed in vacuum as well as in air atmosphere. The wear rate increased with sliding speed in vacuum, on the other hand, in air atmosphere the wear rate decreased with increasing sliding speed, reaching a minimum at a critical sliding speed and then increasing with further increase in sliding speed. The coefficient of friction remained almost constant for different sliding speeds for both air and vacuum. However, under vacuum, the value of coefficient of friction was lower than that in air, through the range of sliding speed. The wear behaviour of the spray formed alloy under different conditions is discussed as inferred from the microstructural features of the alloy and the nature of the worn surfaces of the wear test specimen.