氧燃比对NiCrAlY涂层的微观结构及其在KCl熔盐中热腐蚀行为的影响

Effect of oxygen-fuel ratio on microstructure and hot corrosion behavior of NiCrAlY coatings in KCl molten salt

采用超音速火焰喷涂(HVOF)技术制备氧燃比分别为3.91、4.31、4.62、5.39的NiCrAlY涂层,利用XRD、SEM、EDS、显微硬度计、拉伸试验机分析表征涂层微观组织结构及力学性能的变化规律,进而研究微观组织结构的变化对涂层在KCl熔盐环境中热腐蚀性能的影响。结果表明:随着氧燃比的升高,涂层中γ/γ′峰向高角度偏移,涂层结构变得致密,未熔化粒子边界减少,涂层结合强度由49 MPa提高到62 MPa,涂层显微硬度变化较小。涂层平均热腐蚀质量增加速率常数Kp由93.37 mg^(2)/(cm^(4)·h)降低到1.54 mg^(2)/(cm^(4)·h),说明涂层抗热腐蚀性能随着氧燃比的增大而升高。这主要是由于高氧燃比涂层中较少的孔隙及未熔化粒子边界,使得Cl、O向内扩散通道减少,涂层氯化-氧化程度降低,从而赋予涂层更优异的抗热腐蚀性能。

The NiCrAlY coatings with oxygen-fuel ratio of 3.91,4.31,4.62 and 5.39,respectively,were prepared by high-velocity oxygen fuel spraying(HVOF).The changes of microstructure and mechanical properties of the coating were characterized by XRD,SEM,EDS,microhardness meter and tensile testing machine.Then,the effect of microstructure on hot corrosion behaviors of coatings in KCl molten salt environment was investigated.The results show that,with the increase of the oxygen-fuel ratio,theγ/γ′peak shifts to a high angle,the denser coating structure is obtained and the boundaries of unmelted particles decrease.The coating bonding strength increases from 49 MPa to 62 MPa,while the oxygen-fuel ratio has little effect on the microhardness of the coating.The average hot corrosion rate constant Kp decreases from 93.37 mg^(2)/(cm^(4)·h)to 1.54 mg^(2)/(cm^(4)·h),which implies that the hot corrosion resistance of the coating enhances with the increase of oxygen-fuel ratio.The lower porosity and fewer unmelted particle boundaries in the high oxygen-fuel ratio coating result in the decrease of the diffusion channels of Cl and O.So,the extent of chlorination-oxidation of the coating decreases,thereby,endowing the coating with better hot corrosion resistance.