Zr-Sn-Fe-Cr-(Nb)合金在500℃过热蒸汽中的腐蚀各向异性研究

INVESTIGATION ON THE CORROSIVE ANISOTROPY OF Zr-Sn-Fe-Cr-(Nb) ALLOYS IN 500 ℃ SUPER-HEATED STEAM

选用无织构的Zr-0.72Sn-0.32Fe-0.14Cr和Zr-0.85Sn-0.16Nb-0.37Fe-0.18Cr合金大晶粒片状样品,利用静态高压釜在500℃,10.3 MPa过热蒸汽中进行500 h的腐蚀实验,采用EBSD,SEM和TEM等方法研究了合金的显微组织以及氧化膜的厚度与金属晶粒表面取向的关系.结果表明,Nb对第二相的晶体结构产生影响,Zr-0.72Sn-0.32Fe-0.14Cr合金中的第二相主要为fcc的Zr(Fe,Cr)2,而Zr-0.85Sn-0.16Nb-0.37Fe-0.18Cr合金中的第二相为fcc和hcp的Zr(Nb,Fe,Cr)2;2种合金均未出现疖状腐蚀,并且不同金属晶粒取向上的氧化膜厚度没有明显差别,即没有表现出腐蚀各向异性特征.

Zirconium alloys are widely used as nuclear fuel cladding in water reactors because of their low cross-section for thermal neutron absorption, reasonable mechanical properties and adequate corrosion resistance in high temperature water. Zirconium alloys have a prominent anisotropic characteristic because of the hexagonal close-packed crystal structure. The anisotropic growth of oxide layers is related to corrosion conditions and chemical composition of zirconium alloys. The corrosive anisotropy of Zr-0.72Sn-0.32Fe-0.14Cr and Zr-0.85Sn-0.16Nb-0,37Fe-0.18Cr coarse-grained specimens was investigated in a superheated steam at 500 ℃ and 10.3 MPa by auto- clave tests. EBSD, SEM and TEM were used to investigate the microstructures of the alloys and the relationship be- tween the oxide thickness and the grain orientation of the metal matrix. Results showed that the structures of sec- ond phase particles （SPPs） can be affected by Nb： the face-centered cubic Zr（Fe, Cr）2 precipitates were mainly de- tected in Zr-0.72Sn-0.32Fe-0.14Cr alloy, while the face-centered cubic and hexagonal close packed Zr（Nb, Fe, Cr）2 precipitates were observed in the Zr- 0.85 Sn- 0.16Nb- 0.37Fe- 0.18Cr alloy. No nodular corrosion appeared on the two alloys for 500 h exposure. There was no big difference between the thickness of oxide layers and the grain ori- entations, i.e. no corrosive anisotropy of the two alloys was presented.