Study On Cavitation Erosion Behavior And Mechanism Of Copper Alloy Under Ultrasonic Action

With the advance of cavitation and cavitation erosion principles,it is proved that cavitation erosion impairs the operation efficiency and service life of mechanical equipment,and the waste of energy and materials is caused as well.However,cavitation effects could be utilized to cut,clean and prepare materials and even to exploit oil and gas,adding considerable economy value.At present,due to insufficient knowledge of cavitation and the complexity of the environment in which cavitation erosion occurs,generalizable research conclusions have rarely been reported.Whether it is to prevent cavitation erosion or to make reasonable use of cavitation effects,an in-depth study is necessitated.Among the research equipment of cavitation erosion,ultrasonic cavitation erosion equipment is advantageous with the single-factor control manner and strong effect of cavitation erosion.In this dissertation,the cavitation erosion device with ultrasonic frequencies of about 27.5 kHz was adopted for cavitation erosion experiments on lead-brass alloys,which are widely used in liquid medium environments related to marine engineering.The study is novel in terms of testing lead-brass alloys under the ultrasonic cavitation condition.The cavitation erosion behavior of the lead-brass alloy was inspected from three aspects,namely cavitation erosion distance,liquid medium and surface topography.The process and mechanism of cavitation erosion for the lead-brass alloy were analyzed at different operation parameters.With different distances between the ultrasonic horn and the specimen,the cumulative mass loss,cavitation erosion depth,roughness,micro-morphology,and 3D surface morphology of the specimens were analyzed.Meanwhile,the characteristics of specimen surface and cavitation erosion effect were studied as well.As the vertical distance between the ultrasonic horn and the specimen surface falls between 0.4 and 0.6 mm,the most serious cavitation damage arises and thereby the cavitation erosion effect is the best.Furthermore,such an optimal distance does not vary with cavitation erosion time.Ultrasonic cavitation erosion experiments were performed on lead-brass alloy specimens in tap water,deionized water,and 3.5% sodium chloride solution.The cumulative mass loss,roughness,micro-morphology,3D surface morphology,and hardness were observed and measured after cavitation erosion.The characteristics of the specimen surface were compared and analyzed.The mechanism of the formation,expansion,and destruction of the cavitation erosion was investigated among the three liquid mediums.Cavitation erosion results in hardened layers of hundreds of microns in depth,as is shared by the three liquid mediums.For identical cavitation erosion time,the smallest cumulative mass loss is witnessed in the 3.5 % sodium chloride solution,and the largest hardness value excels its counterpart by 13.6%,demonstrating good resistance of cavitation erosion.Lead-brass alloy specimens with different patterns of surface topography were obtained by means of polishing and sandblasting.The cumulative mass loss,roughness,micro-morphology and residual stress of the specimen were measured after cavitation erosion.Influence of surface morphology on cavitation erosion was compared and analyzed,and the relationship between the cumulative mass loss,roughness,residual stress and cavitation erosion time was constructed.The influence mechanism of surface morphology was explained.It is demonstrated that polishing treatment is more effective than sandblasting processing in alleviating the damage to specimen surface during the early stage of cavitation erosion.With the increase in cavitation erosion time,sandblasted specimen has the initial hardened layer and a secondary hardening effect,the durability of the anti-cavitation erosion ability of the sandblasted specimen is higher than that of the polished specimen,which is ascribed to the existence of initial hardened layer and the secondary hardening effect.Conclusions obtained in this dissertation help to deepen the understanding of cavitation mechanism,and contribute to the design,development and the improvement of anti-cavitation erosion capability of lead-brass alloy mechanical components working in liquid medium.Moreover,applications of cavitation effects are anticipated to be extended.