用高压釜腐蚀实验研究了不同Nb含量的Zr-xNb-0.4Sn-0.3Fe (x=0~1,质量分数,%)合金在360 ℃、18.6 MPa纯水,360 ℃、18.6 MPa、0.01 mol/L LiOH水溶液以及400 ℃、10.3 MPa过热蒸汽中的耐腐蚀性能,用TEM和SEM分析了合金腐蚀前后的显微组织。结果表明,x从0增加至1时,合金在纯水和过热蒸汽中的腐蚀增重逐渐增加,但在LiOH水溶液中的腐蚀增重减少;Nb具有细化合金再结晶晶粒作用,随着Nb含量的增加,合金中第二相直径相接近,但第二相的面密度和Nb/Fe比增大,当x≤0.2时,第二相主要为不含Nb的ZrFe或含少量Nb的ZrNbFe相,0.3≤x≤1时,主要为ZrNbFe相;合金腐蚀速率越高,氧化膜断面平行裂纹越多,基体/氧化膜界面处呈“菜花”状凸起越严重。探论了Nb含量对Zr-xNb-0.4Sn-0.3Fe耐腐蚀性能影响的机理,认为含Nb第二相的析出量是引起合金耐腐蚀性能差别的主要原因。
Zr-Sn-Nb-Fe alloy is one of the high performance zirconium alloys used as the fuel cladding materials for high burnup fuel elements. The corrosion behavior of zirconium alloys were affected by the alloying element, the microstructure and fabricating process. To better understand the effect of Nb on the corrosion behavior of Zr-Sn-Nb-Fe alloy, Zr-xNb-0.4Sn-0.3Fe (x=0~1, mass fraction, %) sheets were prepared by thermo-mechanical processing and tested in static autoclave in 360 ℃, 18.6 MPa pure water, 360 ℃, 18.6 MPa, 0.01 mol/L LiOH aqueous solution, and 400 ℃, 10.3 MPa superheat steam. The characteristics of the microstructure were analyzed by TEM and SEM. It was shown that the corrosion weight gain of specimens was increased when x increaseed from 0 to 1 in pure water and steam. However, it was found that the corrosion weight gain reduced in LiOH aqueous solution as Nb content was increased. The microstructural characteristic indicated the addition of Nb has the effect of refining recrystallization grain of Zr-xNb-0.4Sn-0.3Fe alloy. The mean size of the precipitates in alloy were almost the same even though the Nb was considerably changed, but the area fraction of precipitates and mass ratio of Nb/Fe in precipitates of alloy were increased with the Nb content increasing when all the samples heat-treated in the same condition. The ZrFe or ZrNbFe precipitate of including small amounts of Nb was mainly formed when x was 0.2 or less, and the ZrNbFe precipitate was mainly found when the content of Nb was higher. With the increasing of corrosion rate, there are more cracks in the fracture surface of the oxide films and the size of “Cauliflower-like” structure grows bigger. It was concluded that the contents of Nb in ZrNbFe precipitates will be responsible for the difference of corrosion resistance for Zr-xNb-0.4Sn-0.3Fe alloy.
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