Comparing Different Methods to Determine the Intergranular Oxidation Damage on a Nickel Based Superalloy
Comparing Different Methods to Determine the Intergranular Oxidation Damage on a Nickel Based Superalloy
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比较确定镍基高温合金晶间氧化损伤的不同方法
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
E. Andrieu
中科院分区：
文献类型：
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作者：
V. Garat;O. Brucelle;J. Cloué;V. Rebeyrolle;D. Monceau;B. Viguier;E. Andrieu
将718合金的薄拉伸试样在1000°C下在合成空气中氧化不同的持续时间，然后根据航空热处理（720° C-8h，620°C-8h）进行热处理，然后在室温下在拉伸机上进行测试。对足够薄的样本（厚度小于0.3 mm，标距长度等于200 mm）进行机械试验，以突出受损区域对整体拉伸行为的影响。结果表明，力学行为保持不受影响的流动规律，但在氧化试样的情况下，流动应力显着下降。这种下降首先归因于加载截面的减小，但是这种减小应当比通过SEM或西姆斯测量的晶间氧化面积大30%至40%。为了解释这种差异，氧扩散的晶间氧化前沿的假设提出。为了验证这一假设，使用了一种基于西姆斯分析的新方法。元素浓度分布与成像一起获得后，一个专门设计的方法，允许从金属溅射到氧化物。该分析表明，Al 2 O3在晶间氧化前沿形成，并且在该前沿之前的合金中没有发现可测量的溶解氧，从而使所提出的假设无效。在1000°C真空下处理的试样的拉伸试验表明，高温热处理是机械性能下降的一半原因。最后，将718合金在高温下热处理的薄试样的拉伸曲线与标准曲线进行比较是量化该合金由于处理而造成的损伤的准确方法。
Thin tensile specimens of alloy 718 were oxidized under synthetic air, at 1000°C for different durations, then heat treated according to an aeronautical heat treatment (720°C8h, 620°C-8h) before being tested on a tensile machine at room temperature. Mechanical tests were performed on sufficiently thin specimens (thickness less than 0.3 mm and a gage length equal to 200 mm) in order to highlight the influence of the damaged zone upon the global tensile behavior. It was shown that the mechanical behavior remained unaffected in terms of the flow law but a significant drop in flow stress was seen in the case of oxidized specimens. This drop was at first attributed to a reduction of the loaded section, but this reduction should then be 30 to 40% greater than the intergranular oxidation area measured by SEM or SIMS. To explain this discrepancy, the hypothesis of oxygen diffusion ahead of the intergranular oxidation front was proposed. In order to check this hypothesis, a new method based on SIMS analysis was used. Elemental concentration profiles together with imaging were obtained following a specifically designed method that allowed the sputtering from the metal to the oxide. This analysis showed that Al2O3 forms at the intergranular oxidation front and that no measurable dissolved oxygen is found in the alloy ahead of this front, thus invalidating the proposed hypothesis. Tensile tests on a specimen treated under vacuum at 1000°C suggest that high-temperature heat treatment is responsible for half of the drop in mechanical properties. Finally, comparing the tensile curves of thin specimens of alloy 718 heat treated at high temperature to a standard curve is an accurate method to quantify the damages on this alloy due to the treatment.