基于扫描开尔文探针力显微镜的金属中局部氢分布测试方法研究

Measurement of Local Hydrogen Distribution in Metals Based on Scanning Kelvin Probe Force Microscope

目的探明金属材料中局部氢分布及演化特性是揭示其高压氢脆机理、预测承载件服役性能的重要基础。由于材料中局部氢分布测试难度大,目前各种测试研究方法都存在缺点和不足。方法利用扫描开尔文探针力显微镜(SKPFM)进行金属中局部氢分布研究具有空间分辨率高、测试无损的特点,但其测试结果影响因素多,亟待建立相应的测试可靠性保障方法。较为系统的研究了关键测试参数、试验温度、试验气氛环境等对SKPFM测试结果的影响规律。基于上述影响SKPFM测试结果的因素及其影响规律,建立了相对应的控制策略,完善了基于SKPFM的金属近表面局部氢分布测试方法,并对该方法的有效性进行了验证。最后,利用建立的方法研究了高温高压充氢后S30408中氢分布的演化规律。结果对于特定的激振频率,总存在一个激振相位的最佳区间,在此区间内CPD测试的误差最小,且数据稳定性高,激振频率的变化会导致最佳相位区间的变化;空气中的水分和氧气不仅对CPD整体值影响较大,还改变了不同位置处CPD的差值。根据对高温高压充氢后S30408中氢分布的演化规律的观察,氢在S30408中扩散速度随晶向的不同存在差异性。结论利用SKPFM可以有效的测试金属近表面局部氢分布,为金属材料氢脆机理的研究提供了支撑。

The investigation on localized hydrogen distribution and evolution in metal is an important basis for revealing the mechanism of high-pressure hydrogen embrittlement and predicting the service performance of load-bearing components.Due to the difficulty in testing the local hydrogen distribution in materials,various testing and research methods have shortcomings and deficiencies at present.Scanning Kelvin probe force microscopy(SKPFM)was used to study the characteristics of local hydrogen distribution,including high spatial resolution and nondestructive test.However,since many factors affected the test results,the testing methods able to ensure the reliability of results were set up.The influences of key parameters,test temperature and test atmosphere on SKPFM test results were studied.Then,based on above factors and influence laws on SKPFM test results,corresponding control strategy was established and the SKPFM-based method for measuring the local hydrogen distribution on the near surface of metal was improved and verified for effectiveness.Finally,the established method was applied to investigate the evolution of hydrogen distribution in thermally hydrogen-charged S30408 austenitic stainless steel.For a specific drive frequency,there was always an optimal interval of drive phase.In this interval,the error of CPD test was the smallest and the data stability was high.Changes in drive frequency led to changes in the optimal phase interval.Moisture and oxygen in the air not only had a great influence on the overall value of CPD,but also changed the difference of CPD at different positions.According to the observation of the evolution law of hydrogen distribution in S30408 after charging hydrogen at high temperature and high pressure,the results show that the diffusion rate of hydrogen in S30408 varied with the crystal orientation.SKPFM can effectively test the local hydrogen distribution in metal,which provides support for the study of HE mechanism.