A powder-filled epoxy compound was tested for cavitation wear in the form of bronze particles BraZHNMc9-4-4-1. The particles were obtained by sawing a bronze bar. The composition of the compound was as follows: 100 parts of resin K-153 and 12 parts of hardener (polyethylene polyamine). The specimens were shaped as cylinders, 15.5 and 15 mm in diameter and height, respectively. The tests were carried out with an ultrasonic magnetostrictive vibrator in fresh water at water temperature 20 ± 3 ° C. The frequency and amplitude of oscillations of the vibrator hub end were approximately 22 kHz and 28 μm, respectively. The distance between the end of the concentrator and the end of the specimen wear was set to 0.5 mm. A second-order model describing the cavitation wear as a function of the bronze particle size, its content in the composite and the specific surface area of the particles was constructed by the least-squares method. The cavitation wear of the composite increases with increasing values of these parameters. The greatest influence on composite cavitation wear has the total surface area of bronze microparticles in volume unit.
Two series of tests of annealed metal materials — copper, brass L60 and aluminum-magnesium alloy AMg4,0 — were carried out. The first series consists first in upsetting the cylindrical samples of the listed above alloys on a press to a different strain rate, then cutting the deformed samples and measuring the microhardness of the area adjacent to the center of the samples. The first series results in constructing the calibration plots of microhardness as a function of strain. During the second series the tests of the same materials for cavitation wear were carried out in the fresh water on the ultrasonic vibratory apparatus. The frequency and amplitude of the apparatus horn vibration amount to 22 kHz and 28 μm respectively. The microhardness of the samples surface exposed to cavitation attack was measured after the definite spans of time within the incubation period and the maximum value of the microhardness was registered. Marking the maximum microhardness value on the calibration plot yields the strain rate reached on the surface under cavitation attack before the removal of wear particles begins. On the basis of the found values of the strain the stress state rigidity of the surface layers under cavitation attack was evaluated. The obtained coefficients of stress state rigidity allowed drawing the conclusion, that cavitation attack on the material being tested on the ultrasonic vibratory apparatus occurs through the microjets impacts.
The article analyses the structure of cavitated areas of the ship propeller blades made from aluminum bronzes with different composition. The most informative zones of cavitation wear are the cold-hardening zone and the peripheral one that help estimate the mechanical parameters causing the cavities to collapse. The dents formed on the metal surface in the process of hydrodynamic cavitation wear have spherical parts on their bottoms, in which it is possible to inscribe a circle of a definite diameter. There were conducted the experiments on forcing the ball indentors into the surface of different metal alloys. The first run of the experiments includes forcing of a steel ball with a diameter of 1.588 mm into the surface of 33 alloys with different hardness under the loads of 1 470, 980 and 588 N. The impression diameters were measured using Brinell magnifying glass. There has been found the power dependence between deformation of dents on the metals tested under hydrodynamic cavitation and hardness of the materials, which is similar to the dependence of deformation after forcing the ball indentors into the alloys of different hardness. The second run of the experiments included modeling the cold-hardening zone of the cavitation wear area by repeated forcing the ball indentors with the diameters of 1.588, 2.5, 3.175 and 5.0 mm into the bronze BrAZhNMts9-4-4-1 plates with area of 100 × 50 × 20 mm. Forcing was made into the side 100 × 50 mm previously ground and polished. The equal strain rate in impressions of different diameters was observed during forcing. A direct proportional relationship was obtained between the arithmetic mean deviation of the surface profile and the indenter diameter. The arithmetical mean deviation of the assessed profile of the side plotted against the ball indentor yields a direct proportional relationship. Using the dependence for the case of cavitation attack on the propeller blades helps to infer that the diameter of water jets striking against the propeller blade surface with diameter of 3 700 mm makes about 10 mm. The obtained value allows to choose reasonably the experimental equipment and the parameters of testing the ship propeller materials for cavitation wear.
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