Hastelloy N合金表面激光熔覆NiCoCrAlY涂层在LiF-NaF-KF熔盐中的腐蚀行为研究

Corrosion Behavior in Molten LiF-NaF-KF Salt of NiCoCrAlY Coating Prepared by Laser Cladding on Hastelloy N

采用激光熔覆同步送粉技术在HastelloyN合金表面制备了NiCoCrAlY涂层,研究了HastelloyN基材和含NiCoCrAlY涂层的HastelloyN试样在900℃LiF-NaF-KF熔盐中的腐蚀行为。利用失重腐蚀法评估了试样的耐熔盐腐蚀能力,采用XRD和SEM表征了基材和涂层的物相组成、显微组织和腐蚀形貌,并结合EDS分析了微区成分。结果表明,NiCoCrAlY涂层试样的腐蚀速率仅为Hastelloy N基材的2/3。Hastelloy N基材表现为晶间腐蚀,其中Cr元素沿晶界发生选择性脱溶腐蚀,腐蚀前由γ-Ni和M_6C(M为Ni、Co、Cr等)等物相组成,腐蚀后新析出Co_9Mo_(21)Ni_(20)相。NiCoCrAlY涂层表现为均匀腐蚀,其中Al元素充当"消耗品"由涂层均匀向外扩散,形成的腐蚀产物可阻碍涂层中其它元素的扩散从而保护基材,腐蚀前主要由γ-Ni、Al_(0.983)Cr_(0.017)、AlNi_3等物相组成,腐蚀后只存在γ-Ni相。NiCoCrAlY涂层显著提高了基材的耐熔盐腐蚀性能。

A NiCoCrAlY coating has been prepared on Hastelloy N substrate by the powder-feeding laser cladding technique.The corrosion behaviors in molten LiF-NaF-KF（FLiNaK） salt at 900℃ for 100 h were studied for both the substrate and the coating.The corrosion resistance in molten FLiNaK salt was evaluated by the corrosion mass loss method,while the microanalysis on phase constitution,morphologies and composition were carried out by XRD,SEM and EDS.The results show that the corrosion rate of the NiCoCrAlY coating is merely two thirds of that of the Hastelloy N substrate.The substrate is characterized by intergranular corrosion and the element Cr is selectively corroded along the grain boundary.The original Hastelloy N consists of γ-Ni and M6C,and a new Cr9Mo21Ni20 phase is precipitated after the corrosion test.The NiCoCrAlY coating exhibits homogeneous corrosion,in which the element Al diffuses outwards and the corresponding Al-rich corrosion products act as the barrier and thus protect the substrate by impeding the diffusion of other elements.The laser-cladded coating is composed of γ-Ni,AlNi3 and Al0.983Cr0.017,and only γ-Ni remains after the corrosion test.The corrosion resistance of Hastelloy N in molten FLiNaK salt is greatly improved by the laser-cladded NiCoCrAlY coating.