Effect of Surface State on Nodular Corrosion Resistance of Zircaloy-4 Alloy

doi:10.1007/s40195-014-0192-6

Abstract

Abstract:

The effect of surface state on the nodular corrosion resistance of Zircaloy-4 alloy was investigated in superheated steam at 500 °C/10.3 MPa by autoclave tests. The microstructures of oxide films on the corroded specimens were observed by TEM and SEM. The results indicate that surface strained layer delays the appearance of nodular spots on the specimen surfaces and improves the nodular corrosion resistance. The columnar grains orientation of the oxide films formed on the specimens with surface strained layer was more consistent than that on the specimens without surface strained layer when a comparison was made on the same orientation of the grain surfaces. Such a kind of oxide microstructure formed on the specimens with surface strained layer can hinder the diffusion of oxygen ions along the grain boundaries and delay the growth of oxide films, therefore retard the formation process of nodular spots. This indicates that the microstructure of the initial oxide films has an important influence on the subsequent growth of the oxide films.

Key words: Zircaloy-4, Surface strained layer, Nodular corrosion resistance, Microstructures

Chuan-Ming Chen, Bang-Xin Zhou, Shao-Qiu Gou, Jiao Huang, Mei-Yi Yao. Effect of Surface State on Nodular Corrosion Resistance of Zircaloy-4 Alloy[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(2): 254-260.

Figures/Tables 6

Fig. 1 Surface morphologies of Zircaloy-4 specimens without a and with b surface strained layer corroded in superheated steam at 500 °C/10.3 MPa for different time

Fig. 2 Weight gain versus exposure time of Zircaloy-4 specimens without and with surface strained layer corroded in superheated steam at 500 °C/10.3 MPa

Fig. 3 Outer surface morphologies of oxide films formed on Zircaloy-4 specimens without a and with b surface strained layer corroded in superheated steam at 500 °C/10.3 MPa for 0.5 h

Fig. 4 Fracture surface morphologies of oxide films formed on Zircaloy-4 specimens without a and with b surface strained layer corroded in superheated steam at 500 °C/10.3 MPa for 7 h

Fig. 5 Bright-field TEM images showing the orientations of metal grains a, c and dark-field TEM images showing the oxide films formed on the grains b, d of the specimens without a, b and with c, d surface strained layer corroded in superheated steam at 500 °C/10.3 MPa for 0.5 h

Fig. 6 SAED patterns of oxide films formed on the grains without a and with b surface strained layer corroded in superheated steam at 500 °C/10.3 MPa for 0.5 h (the diffraction spots are selected in the dark-field images of oxide films in Fig. 5b, d, which are circled)

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