Study On The Failure Mechanism Of Materials Under The Combined Action Of Cavitation And Corrosion

Marine equipment is not only affected by corrosion,but also damaged by air erosion,which leads to the deterioration of equipment performance,seriously affecting the service life and safety.It has been shown that the damage caused by cavitation corrosion at the same time will be greater.However,the research on cavitation erosion and corrosion combined failure is relatively few,and the failure mechanism is not clear.Therefore,the purpose of this paper is to explore the joint action of cavitation erosion and corrosion on material surface damage,in order to provide theoretical basis and practical guidance for further exploration of the joint action mechanism of the two.In this paper,ultrasonic vibration cavitation test equipment is used to carry out cavitation corrosion test on 45~#steel by changing the experimental technology,cavitation corrosion time and solution concentration.The law of cavitation corrosion failure of 45~#steel under different experimental conditions is analyzed and its inducing mechanism is discussed.The main research results are as follows:(1)Large area corrosion pits are produced on the surface of corrosion samples,showing black spots and yellow spots of different sizes;On the surface of cavitation samples,there are small cavitation pits with uneven dispersion,showing a rainbow ring.The surface morphology failure of the sample is characterized by both corrosion and cavitation.There is no large corrosion pit on the surface of the sample after cavitation corrosion,and the cavitation pit and its rainbow ring have little change.The size of pits generated by cavitation corrosion samples increases significantly,with the center of pits showing black brown and the color of the outer ring gradually becoming lighter.In addition,"trailing"pits are generated near the edge of the samples,and the surface of the samples also becomes yellow.(2)At the same time,corrosion damage degree is greater than cavitation damage degree;The damage degree of corrosion before cavitation erosion is greater than that of corrosion after cavitation erosion.Corrosion has a certain inhibition effect on subsequent cavitation erosion,which may be due to the formation of chloride protective film on the surface after corrosion and the formation of water film on the rough surface after corrosion,while cavitation corrosion has a stronger inhibition effect on subsequent corrosion,which is related to the passivation film formed on the surface at high temperature and work hardening.The damage degree of the combined action of cavitation erosion and corrosion on 45~#steel is much stronger than that of single cavitation erosion or corrosion,but also more serious than that of first cavitation erosion and then cavitation erosion,showing the mechanism of mutual promotion of corrosion and cavitation erosion.(3)With the increase of cavitation time,the surface damage of 45~#steel becomes more and more serious.The failure rate was small within 5 min,increased within 10～15min,and further increased within 15～20 min,but the failure rate decreased.The microhardness of sample surface increases with the increase of time,and the increasing range decreases gradually,which is related to the work hardening in the cavitation process.In addition,the corrosion current density of the sample increases gradually,and the corrosion speed is accelerated.The corrosion potential is negative and the corrosion resistance decreases gradually.(4)With the increase of solution concentration,the surface damage of 45~#steel becomes more and more serious,and the change of medium from deionized water to 2%Na Cl solution is the most obvious.When the concentration of Na Cl solution changes from 2%to 3.5%,the damage rate is relatively high,and when the concentration changes from 3.5%to 5%,the damage rate decreases relatively.The microhardness of the sample surface increased,and the increasing range decreased gradually.In addition,the corrosion current density of the sample increases gradually,and the corrosion speed is accelerated.The corrosion potential is negative and the corrosion resistance decreases gradually.In addition,the increase of current density and the degree of negative potential shift gradually decrease,which is related to the competitive adsorption after the increase of Cl~- concentration.