锆合金在失水事故(loss of coolant accident,LOC A)下的高温蒸汽氧化行为是需要重点关注的问题之一.采用非自耗真空电弧炉熔炼了 Zr-xNb(x=0.5、1.0、1.5,质量分数,％)和Zr-1.0Nb-yCr(y=0.05,0.2,质量分数,％)合金并制备成板状样品.采用同步热分析仪研究了 5种锆合金在模拟LOCA工况下900-1200 ℃蒸汽中的氧化行为,利用金相显微镜观察分析了氧化样品横截面的显微组织,使用显微硬度仪测试氧化前后样品的显微硬度.结果显示:在900-1100 ℃蒸汽中氧化时,Zr-xNb合金的抗高温蒸汽氧化性能不随Nb含量变化呈单一变化规律,且随温度的升高发生变化,添加0.05％和0.2％(质量分数)的Cr使Zr-1.0Nb合金的抗高温蒸汽氧化性能变差;在1200 ℃蒸汽中氧化时,添加Nb和Cr对锆合金的抗高温蒸汽氧化性能影响不大;5种合金的氧化动力学规律随温度升高发生变化,总体由抛物线→直线规律转变,还会发生多次转折.从O在Zr基体中的固溶含量以及Zr基体α↔β和氧化膜单斜(m)↔四方(t)相变的角度探讨了Nb和Cr影响锆合金高温蒸汽氧化行为的机制.
High Temperature Steam Oxidation Behavior of Zr-xNb-yCr Alloys
The high temperature steam oxidation behavior of zirconium alloys under loss of coolant accident(LOCA)is one of the issues that needs to be focused on.Zr-xNb(x=0.5,1.0,1.5,wt％)alloys and Zr-1.0Nb-yCr(y=0.05,0.2)alloys were smelted by non-consumable vacuum arc furnace and then they were prepared into plate samples.The oxidation behavior of the five zirconium alloys in steam at 900-1200 ℃ under simulated LOCA conditions was investigated by a simultaneous thermal analyzer.And the microstructure and microhardness of the samples before and after oxidation were studied by a metallographic microscope and a microhardness tester,respectively.The results show that the oxidation resistance to high-temperature steam of Zr-xNb alloys does not vary monotonically with the change of Nb content at 900-1100 ℃,and changes with temperature;the addition of 0.05wt％and 0.2wt％Cr makes the oxidation resistance to high-temperature steam of Zr-1.0Nb alloys worse.When the alloy is oxidized in steam at 1200 ℃,the addition of Nb and Cr has little effect on the oxidation resistance to high temperature steam of the alloys.With the increase in temperature,the oxidation kinetic of the five alloys undergoes a parabolic→ linear transition with multiple transitions.Finally,the mechanism that Nb and Cr affect the high temperature steam oxidation behavior of zirconium alloys is derived from the following perspectives:the solid solution content of O in the Zr matrix,the α↔β phase transition of the Zr matrix and the monoclinic(m)↔tetragonal(t)phase transition of the oxide film.
zirconium alloyloss of coolant accidenthigh-temperature steam oxidationmicrostructurephase transition
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