Wear resistance of titanium-alloyed high-aluminum bronzes under cavitation

Abstract

Alumintan-nickel bronzes are known to have a high cavitation-erosion resistanceThe cavitation resistance of A1-Ni bronzes and the effect of additions of Ti on them were studied in [1][2][3].In our work we studied the properties of cast bronzes with an aluminum content of 11-12 and 14-15% (Table 1). The bronzes were cast in electric furnaces into cylinders 30 nml in diameter, from which specimens were cut for cavitation wear tests. The experiments were carried out on a magnetostrictive vibrator with a 22-kHz concentrator. Specimens of diameter 15 mm and thickness 7 mrn were clamped in a mandrel so that the surface of the specimens was 0.5 mm from the end of the concentrator. The amplitude of the concentrator-end vibrations was 33 ~m. The tests were conducted in fresh water at 20 + 2°C.The surfaces of all of the specimens were polished before the tests. During the tests the specimens were removed from the mandrel, dried, and weighed to within 0.05 rag. The kinetic cavitation-wear curves were plotted on the basis of the measured masses of the specimens. The kinetic curves were then used to find the accumulation (incubation) period 7"ac c of the cavitation erosion, i.e., the period when there is no catastrophic wear. The period racc was determined from the point of intersection of a tangent to the kinetic wear curve and the horizontal axis. The tangent was drawn through the point corresponding to the maximum wear rate. The decrease in mass AG after 7.5 h of testing was used as the wear index. The AG and ra¢c characteristics given in Table 1 for each bronze were determined as the average result of two parallel tests. The mechanical characteristics, i.e., the microhardness H (under a load of 1 N) and the elastic modulus E (Table 1), were measured with a PMT-3 machine on polished specimens before the experiment began. The microhardness of the individual structural components was determined under a load of 0.50 N. The elastic modulus was evaluated by the method of [3]. A Mikrolift-2 attachment to the microhardness meter, making it possible to record the depth of the indentation under a load, enabled us to use this method [4].The relative cavitation-erosion resistance of AI-Ni-Ti bronzes is given in Table 2.The effect of additional titanium alloying of aluminum-nickel bronze on its cavitation-erosion resistance is illustrated in Fig. 1. The experimental points in Fig. 1 are grouped satisfactorily about two curves, having the form of an exponential Content of elements, %