Cavitation erosion of copper and copper-based alloys
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NTRODUCTION
CAVITATION, a repeated formation and violent collapse of bubbles in a liquid created by pressure changes, can result in deformation and erosion of material in the vicinity of the bubbles. It has been shown that the stress, which is responsible for erosion, can be due to the concerted collapse of the whole aggregate of bubbles and/or due to the impact of microjets or stress pulses from the collapse of individual bubbles.[1,2] As cavitation erosion is known to occur in many engineering situations, attempts have been made to correlate the resistance of a metal to erosion with some mechanical properties such as hardness, fatigue, or strain energy. However, the attempts failed when a wide range of materials were analyzed.[3,4,5] Thus, comprehensive descriptions of the erosion mechanism have been involved to account for the different responses among different materials. For example, such studies have been reported for fcc metals and their solid-solution alloys,[2] iron and steel,[6] iron- and cobaltbased alloys,[7] age-hardenable aluminum alloys,[8] NiAl intermetallic compounds,[9] and copper- and tin-based alloys.[10] Based on microscopic studies of damage, a good explanation for the erosion resistance of the materials has been found. The present work is aimed at understanding the cavitation erosion behavior of copper and copper-based alloys. Singlephase ␣-solution alloys and multiphase alloys for a screw propeller application were involved, the latter being studied to put them into use. II. EXPERIMENTAL PROCEDURE Table I shows the chemical composition of the copperbased alloys tested. The materials are divided into two groups: single-phase ␣-solution alloys and multiphase alloys. They were designated according to their composition.
´ SKA and M. GŁOWACK, Assistant Professors, are with the J. HUCIN Mechanical Faculty, Technical University of Gdan´sk, 80-952 Gdan´sk, Poland. Manuscript submitted March 3, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS A
The following alloys, which are ␣-phase in structure, were studied: Cu99.7 commercial copper, CuZn30 brass, and CuAl5 bronze. The multiphase alloys were of complex chemical composition and included CuZn40Mn3Fe1 brass, CuMn17Zn6Fe5Al3 bronze, CuMn12Al7Fe3Ni3 bronze, CuAl10Fe3Mn2 bronze, and CuNi5Fe5Al4Mn1 bronze. Two materials, Cu99.7 copper and CuZn30 brass, were received in the form of mill-annealed plates of 12 mm in thickness, while the rest of the alloys were in form of 12-mm-thick plates which were cast into sand molds. The alloys densities were measured, and the microstructure and the average grain size were examined. The results are listed in Table II. The mechanical properties of the alloys are presented in Table III. Cavitation erosion was produced by using a well-known and widely used vibratory system.[1,11] A schematic cross section of the test equipment is shown in Figure 1. The device consists of a magnetostrictive transducer oscillating at a 6.5 kHz frequency and an exponential horn which amplifies the vibration amplitude. The horn carries a threa
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