Zr-4合金腐蚀初期氧化膜的显微组织研究

INVESTIGATION OF MICROSTRUCTURE OF OXIDE LAYERS FORMED INITIALLY ON Zr-4 ALLOY

用Zr-4合金的大晶粒样品在360℃/18.6 MPa的0.01 mol/L LiOH水溶液中进行5 h的腐蚀实验,借助SEM,EBSD和HRTEM等分析方法,研究了腐蚀初期氧化膜生长的各向异性、显微组织和氧化物结构.氧化膜的厚度因基体表面晶粒取向不同而有差异(376-455nm),在基面(0001)和棱柱面(01(?)0)附近晶面上生长的氧化膜最厚;氧化膜由单斜、立方和四方结构的氧化物组成;氧化膜的结构和晶粒取向分布也随基体晶粒取向不同而存在差异,在(0001)附近晶面上生成的氧化膜中氧化物结构种类较多、晶粒取向差别较大,这种氧化膜的显微组织在腐蚀过程中可促使氧化膜更快生长.

Zr-4 specimens with coarse grain of 0.2--0.8 mm were prepared to investigate the anisotropic growth of oxide layers formed initially on the grain surface with different orientations during corrosion tests in autoclave at 360 ℃/18.6 MPa in 0.01 mol/L LiOH aqueous after 5 h exposure. SEM, EBSD and HRTEM were adopt to measure the thickness of oxide layers, to determine the grain orientation of the matrix surface and to investigate the microstructure of oxide layers. The thicknesses of oxide layers formed on different grains varied in the range of 376--455 nm. The thickest oxide layers were detected on the grains with the orientations nearby basal plane （0001） and prismatic plane （0110）. The oxide layers have monoclinic, cubic, tetragonal crystal structures. Besides the thickness difference of oxide layers, the crystal structure and misorientation of nano-grains in oxide layers formed on different grains were also significantly different, and the most complicated oxide layer was formed on the grain with orientation nearby （0001） plane. Such kind of microstructure has more crystal defects, and larger ability for promoting the diffusion of oxygen ions and the growth of oxide layer.