超临界水环境中三种Ni-Cr涂层氧化特性研究

Oxidation Behavior of Three Different Ni-Cr Coatings in 630℃/25 MPa Supercritical Water

开展了汽轮机用FB2钢及3种工艺制备的热喷涂Ni-Cr涂层在630℃/25 MPa超临界水环境氧化实验研究。利用电子天平、SEM、XRD以及XPS对材料的氧化动力学、氧化膜微观形貌、物相成分进行了分析。结果表明:由于实验过程氧化膜发生剥落,FB2钢氧化动力学偏离抛物线规律,而不同工艺制备涂层的氧化动力学严重偏离抛物线规律。FB2材料氧化膜为典型的双层结构,外层富铁由Fe_(3)O_(4)或Fe_(2)O_(3)组成,内层由富铬尖晶石组成;涂层的表面氧化物主要是富铬氧化物。FB2钢和涂层的氧化膜物相成分都随着氧化时间增加而发生变化。同时讨论了FB2材料及3种表面涂层在超临界水中的氧化机理。

Oxidation behavior of FB2 steel for steam turbine and FB2 steel coated with three different coatings was comparatively investigated in 630℃/25 MPa supercritical water(SCW).The three coatings are supersonic flame spraying Ni-Cr coating(SFS-NiCr),glass shot peened SFS-NiCr and emery belt grinded SFS-NiCr.Their oxidation mass change was intermittently measured by electron balance,while their microstructure and phase composition were characterized by means of SEM,XRD and XPS before and after oxidation test.Results show that the oxidation kinetics curve of FB2 material deviated from the parabola due to the spallation of the formed oxide scale during the oxidation process.The oxidation kinetics curves of coatings prepared by different processes seriously deviated also from the parabola.A double-layered oxide scale formed on FB2 steel,consisting of an Fe-rich outer Fe_(3)O_(4),Fe_(2)O_(3) and a Cr-rich inner oxide layer.The oxide scale formed on the three coatings are mainly composed of chromium-rich oxide.The phase composition of the oxide scales formed on FB2 steel and the three coatings changed with the increase of oxidation time.Finally,the oxidation mechanism of FB2 steel and three coatings in supercritical water was discussed.