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核级Zr-4合金微量水蒸气短期氧化行为研究
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摘要
针对核级Zr-4合金材料的服役环境,建立了Zr-4合金微量水汽配置及氧化动力学特性研究联合实验装置,开展了Zr-4合金材料在微量水汽含量为8~795 ppm、温度350~450℃范围内短期(24 h)氧化动力学实验。结果表明,Zr-4合金在350℃,400℃和450℃氧化时,其氧化动力学分别符合立方及平方抛物线生长规律,其氧化速率常数分别为2.17×10~(-8)g~2·cm~4·s~(-1),2.91×10~(-7)g~2·cm~4·s~(-1),1.59×10~(-6)g~2·cm~4·s~(-1);随着温度升高,Zr-4合金氧化速率常数随之增加,在400℃时发生由立方曲线向平方抛物线氧化生长规律的转变;Zr-4合金在较低水汽含量(8~101 ppm)条件下氧化,初期生成含t-ZrO_2与m-ZrO_2的致密氧化膜;而在较高水汽含量(735~795 ppm)条件下氧化易快速形成疏松的m-ZrO_2相,无法形成有效的保护性氧化膜来防止后续的氧化。
To study the short-term oxidation behavior of the nuclear grade Zircaloy-4(Zr-4) alloy in operation condition,a low pressure water vapor generator combined with Thermo Gravimetric Analyzer(TGA) device was established to carry out the oxidation kinetic experiments.The experiments were launched at low moisture content of 8 ppm-795 ppm with the range of temperature between 350 ℃ and 450 ℃ in short-term(24 h) oxidation.The results showed that the oxidation kinetics was fit for cubic and square parabolic growth rule,respectively.The oxidation kinetic constants were 2.17E-08 g~2 · cm~4 · s~(_1),2.91E-07 g~2 · cm~4 · s~(_1),1.59E-06 g~2 · cm~4 · s~(_1),while the Zr-4 alloy were oxidized at 350 ℃,400 ℃ and 450 ℃.With the increasing temperature,the Zr-4alloy oxidation rate constants increased.The oxidation rate change point occurred at 400 ℃.Under oxidizing in the lower moisture content(8 ~101 ppm) conditions,Zr-4 alloy generates portion dense t-ZrO_2 and m-ZrO_2 mixed oxide film.While at higher moisture content(735 ~ 795 ppm) conditions,Zr-4 alloy is easily oxidized rapidly to form a loose m-ZrO_2 phase and unable to form an effective protective oxide film to prevent the subsequent oxidation.
引文
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