等离子喷涂Ni基合金涂层热腐蚀行为研究

Study of hot corrosion behavior of nickel-based alloy coatings sprayed by plasma spraying technology

为探究Ni基合金涂层的热腐蚀防护机理,采用等离子喷涂法在304不锈钢表面制备了NiCr和NiAl两种合金涂层,以75%Na_(2)SO_(4)+25%NaCl的混合盐溶液为腐蚀介质,研究了涂层在700℃下的热腐蚀情况。分别使用扫描电子显微镜、X射线衍射仪对涂层的热腐蚀形貌和晶相变化进行表征,并绘制了涂层的热腐蚀动力学曲线。结果表明:NiCr涂层具有最低的单位面积热腐蚀增重量,经历168 h热腐蚀后以尖晶石结构物NiCr_(2)O_(4)晶相为主,能有效阻挡外界腐蚀物向金属基体的侵蚀;在氯化物的高温挥发下,NiAl涂层中早期形成的Al_(2)O_(3)保护膜被破坏,外界Cl和S的化合物沿着孔隙和裂缝侵入基材内部,引起涂层失效;同种腐蚀环境下,NiCr涂层较之NiAl涂层具有更优良的热腐蚀防护性能。

In order to explore the hot corrosion protective mechanism of Ni-based alloy coating,two alloy coatings,NiCr and NiAl,were prepared on the surface of 304 stainless steel by plasma spraying.The mixed salt solution of 75%Na2SO4+25%NaCl was used as the corrosive medium,and the hot corrosion behavior of coatings was studied at 700℃.Scanning electron microscope(SEM)and X-ray diffractometer(XRD)were used to characterize the hot corrosion morphology and crystal phase change of the coating,and the hot corrosion kinetic curves of the coating were described.It has been revealed that NiCr coating has the lowest weight gain by hot corrosion per unit area,and after 168 h of hot corrosion,crystal phase of spinel structure NiCr2O4 is dominant,which could effectively prevent external corrosive substances from penetrating into the metal matrix;that under the high temperature volatilization of Cl compounds,the early formed Al2O3 protective film of NiAl coating is destroyed,thus the external Cl and S compounds penetrate into the substrate along the pores and cracks inside the coating,causing the coating′s failure;and that under the same corrosive circumstance,NiCr coa-ting performs better in terms of hot corrosion protection than NiAl coating.