激光重熔镍铝青铜组织、腐蚀及空蚀行为研究

Microstructure,corrosion and cavitation erosion behavior of laser surface melted nickel aluminum bronze

镍铝青铜(NAB)是制备船用螺旋桨的重要材料。针对铸态NAB组织粗大且不均匀,影响螺旋桨使用寿命的问题,采用激光重熔(LSM)对铸态NAB表面进行改性处理。结果表明,LSM显著细化了铸态组织,LSM NAB重熔区组织为细小柱状晶,柱状晶长轴垂直于熔池界面,热影响区组织为晶粒较为粗大的等轴晶及柱状晶。LSM NAB的硬度可达285~325 HV,较铸态提高50%~70%。电化学测试结果显示,LSM NAB与铸态NAB在3.5%Na Cl溶液中的电极反应过程类似,但LSM NAB的阴极过程较铸态缓慢,因此腐蚀速率低于铸态NAB。超声振动空蚀实验结果表明,由于硬度的提高和组织的均匀化,LSM NAB空蚀失重率可降至铸态的3/5,且表面发生均匀损伤,无铸态表面较大的空蚀坑。

Nickel aluminum bronze （NAB） is one of the main materials used for making ship propellers. Large ship propellers are generally castings. The coarse and inhomogeneous microstructure of the cast NAB will reduce the lifetime of the ship propellers. ｜n present study, laser surface mehing（I.SM） is applied to modify the cast microstructure. The results show that the LSM significantly refines the cast microstructure. The melting zone contains fine columnar grains,and the major axis of the columnar grains is perpendicular to the interface of the molten pool. The heat affected zone （HAZ） consists of coarse isometric and columnar grains. The hardness of the LSM NAB can reach 285- 325 HV,which is increased by 50%-70% comparing with the hardness of the cast one. The electrochemical measurement results show that the LSM NAB and cast NAB experience similar electrode reaction processes in 3.5% NaCI solution. However,comparing with the cast NAB, the cathode process of the LSM NAB is slower and therefore the corrosion rate is slower. The ultrasonic vibration cavitation erosion test results show that the erosion rate of the LSM NAB is only 60% of that of the east one because of ttle increased hardness and refined microstructure. For LSM NAB,the damaged surface is much evener,and no large cavitation erosion pit is found. And the effect of LSM parameters on the microstructure,corrosion and cavitation erosion behavior is also discussed.