304不锈钢点蚀声发射监测研究

为研究304不锈钢在高于常温条件下的点蚀声发射特性,对70℃下6%氯化铁溶液中304不锈钢点蚀过程进行了声发射监测。采用参数和波形分析相结合的方法处理信号,并通过点蚀形貌观察进行验证。结果表明声发射撞击和能量随时间逐渐增加,在某一时段达到峰值,随后下降并维持平稳状态。信号波形主要由幅度、能量较大的低频段(<100kHz)弯曲波和幅度、能量较小的高频段(>100 kHz)扩展波构成。研究结果对304不锈钢高于常温条件下声发射点蚀监测具有一定意义。     

金属点蚀过程声发射源机制研究

研究了腐蚀特别是点蚀过程产生应力波,即声发射(AE)的源机制,估算了单个钝化膜破裂所产生的薄板表面位移量级,并用实验进行了论证。作者提出,利用板波声发射理论加上参数识别方法,可将腐蚀过程产生的声发射信号同背景噪声相区别。     

Research on acoustic emission characteristics of local corrosion on Q235 steel

To solve the problem of corrosion acoustic emission(AE) source feature extraction and recognition,the AE detection validation and the amplitude-frequency characteristics were derived in theory.The amplitude of AE signal generated by bubble burst is proportional to its radius square and the liquid level,while the AE signal frequency is inversely proportional to the bubble radius.The AE signal amplitude of the steel and the steel corrosion product cracking is proportional to the local stress,and the AE signal frequency is proportional to the crack propagation velocity and inversely proportional to the crack propagation distance.Three Q235 specimens were separately immersed in the solution of 10%FeCl_3·6H_2O,5%CuSO_4·5H_2O and10%FeCl_3·6H_2O with 0.01 mol/L HCL.The AE systems with high frequency and low frequency were used to detect the whole corrosion process AE signals.The AE signals of Q235 steel and the steel corrosion products cracking were detected as the verification experiment.The AE signals from different sources could be distinguished by AE hits count and the power spectrum.It is coincident with theoretical analysis.These conclusions have significant guidance for the corrosion detection and evaluation by on-line acoustic emission detecting.     

Q235钢板局部腐蚀声发射信号特性研究

为解决腐蚀声发射源特征提取和识别的难题,直接从理论上证明了腐蚀声发射监测的有效性并推导出声发射信号特征。气泡破裂声发射信号幅值近似与气泡半径平方和液位高度成正比,频率与气泡半径成反比;钢板及其腐蚀产物开裂声发射信号幅值与开裂位置局部应力强度成正比,频率与裂纹扩展速度成正比,与裂纹扩展距离成反比。用低频和高频两套声发射系统,同时长时间监测Q235钢板在10%FeCl_3·6H_2O、10%FeCl_3·6H_2O加0.01 mol/L HCl混合液、5%CuSO_4·5H_2O溶液中的腐蚀情况,辅以监测钢板及钢板腐蚀产物开裂作为验证实验。通过对声发射信号的参数及谱分析,得出不同声发射源可以通过撞击数及功率谱在频域的分布来有效区分。实验结果与理论分析相吻合,研究结果对腐蚀声发射监测技术具有重要指导意义。     

Q235钢板局部腐蚀声发射信号特性研究

为解决腐蚀声发射源特征提取和识别的难题,直接从理论上证明了腐蚀声发射监测的有效性并推导出声发射信号特征。气泡破裂声发射信号幅值近似与气泡半径平方和液位高度成正比,频率与气泡半径成反比;钢板及其腐蚀产物开裂声发射信号幅值与开裂位置局部应力强度成正比,频率与裂纹扩展速度成正比,与裂纹扩展距离成反比。用低频和高频两套声发射系统,同时长时间监测Q235钢板在10%FeCl₃·6H₂O、10%FeCl₃·6H₂O加0.01 mol/L HCl混合液、5%CuSO₄·5H₂O溶液中的腐蚀情况,辅以监测钢板及钢板腐蚀产物开裂作为验证实验。通过对声发射信号的参数及谱分析,得出不同声发射源可以通过撞击数及功率谱在频域的分布来有效区分。实验结果与理论分析相吻合,研究结果对腐蚀声发射监测技术具有重要指导意义。     

Ultrasonically enhanced corrosion of 304L stainless steel II: the effect of frequency, acoustic power and horn to specimen distance

The effects of frequency in the range 20 to 60 kHz, acoustic power and horn to specimen distance on the corrosion of 304L stainless steel in an ultrasonic field were investigated. At 40 and 60 kHz, the corrosion rate increased to a maximum and thereafter decreased with increasing transmitted power. At 20 kHz, the corrosion rate increased continuously with increasing power over the range investigated. At 18 W transmitted power, the corrosion rate increased continuously with frequency. However, at 40 W transmitted power a pronounced maximum in the corrosion rate occurred at 40 kHz. A significant effect of horn to specimen distance was found, the corrosion rate increasing with decreasing distance. High corrosion rates in excess of 800 mm yr(-1) were observed when the specimen was situated 0.1 mm from the radiating face of the ultrasonic probe. In addition, the area affected by sonication was found to increase with increasing distance.     

Multi-layer structures including zigzag sculptured thin films for corrosion protection of AISI 304 stainless steel

To increase corrosion resistance of the sample,its electrical impedance must be increased.Due to the fact that electrical impedance depends on elements such as electrical resistance,capacitance,and inductance,by increasing the electrical resistance,reducing the capacitance and inductance,electrical impedance and corrosion resistance can be increased.Based on the fact that these elements depend on the type of material and the geometry of the material,multilayer structures with different geometries are proposed.For this purpose,conventional multilayer thin films,multilayer thin film including zigzag structure(zigzag 1)and multilayer thin film including double zigzag structure(zigzag 2)of manganese nitride are considered to protect AISI 304 stainless steel against corrosion in salt solution.These multilayer coatings including zigzag structures are prepared by alternately using the conventional deposition of thin film and glancing angle deposition method.After deposition,the samples are placed in a furnace under nitrogen flux for nitriding.The cross sections of the structures are observed by field emission scanning electron microscopy(FESEM).Atomic force microscope(AFM)is used to make surface analyses of the samples.The results show that the multilayer thin films including zigzag structures have smaller grains than conventional multilayer thin films,and the zigzag 2 structure has the smaller grain than the other two samples,which is attributed to the effect of shadowing and porosity on the oblique angle deposition method.Crystallography structures of the samples are studied by using x-ray diffraction(XRD)pattern and the results show that nitride phase formation in zigzag 2 structure is better than that in zigzag 1 structure and conventional multilayer thin film.To investigate the corrosion resistances of the structures,electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization tests are performed.The results reveal that the multilayer thin films with zigzag structures have better corrosion protection than the conventional multilayer thin films,and the zigzag structure 2 has the smallest corrosion current and the highest corrosion resistance.The electrical impedances of the samples are investigated by simulating equivalent circuits.The high corrosion resistance of zigzag 2 structure as compared with conventional multilayer structure and zigzag 1 structure,is attributed to the high electrical impedance of the structure due to its small capacitance and high electrical resistance.Finally,the surfaces of corroded samples are observed by scanning electron microscope(SEM).     

Ultrasonically enhanced corrosion of 304L stainless steel I: the effect of temperature and hydrostatic pressure

A systematic study of the effect exerted by various parameters on the corrosion of 304L stainless steel in an ultrasonic field has been carried out. Ultrasound increased the corrosion rate under all the investigated conditions. In this paper, attention is focused on the effect of temperature and hydrostatic pressure. At ambient pressure, increase in temperature, T, was found to increase the ultrasonically enhanced corrosion rate up to a maximum of 40 degrees C; at 50 degrees C a marked decrease in the effect of ultrasound was observed. At constant temperature, increase in hydrostatic pressure caused a strong increase in corrosion rate to values in excess of 2500 mm yr(-1) at 4 bar.     

Inhibition of steel pitting corrosion in HCl by some inorganic anions

The effect of Mn and V content on corrosion behavior of mild steel in different concentration of HCl was investigated. The increase of Mn and V content in the steel sample leads to increasing corrosion resistance. The effect of phosphate, molybedate and chromate anions on the corrosion of steel in HCl solution has been studied using weight loss, potentiodynamic and scanning electron microscope (SEM) techniques. The addition of increasing concentrations of phosphate, molybedate and chromate anions causes a shift of the pitting potential (E_pit) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. The phosphate anion has a stronger inhibitive effect of the pitting corrosion. The inhibition efficiency (IE) of different inhibitors increases with the increasing of phosphate concentration and decreases with the increasing the concentration of molybedate and chromate anions. The presence of these anions inhibits the pitting corrosion of steel samples in the order phosphate > molybedate > chromate. The effect of different inorganic anions on the corrosion behavior of two different composition steel samples was also studied in HCl solution.     

Corrosion monitoring of stainless steel 304L in lithium bromide aqueous solution using transmittance optical detection technique

We report a method based on the power ratio of transmittance for monitoring the corrosion rate in stainless steel 304L immersed in an aqueous solution of lithium bromide at 50 wt%, at 70 °C. The optical transmittance measured in the solution contaminated with corrosion oxides at different times of exposure is related to the physical degradation of the stainless steel samples. Lasers at 532 and 632 nm were utilized for monitoring the accumulation of corrosion oxides dissolved in the lithium bromide solution of the metallic samples for 480 h. The change in the optical power of transmittance was 13 μW/480 h measured at 532 nm and 3.6 μW/480 h at 632 nm. The variation of the power ratio for 532 nm was from 0.01 to 0.24, and for 632 nm, from 0.01×10⁻³ to 15.61×10⁻³; this is proportional to an accumulated corrosion rate of [0.0142×10⁻³–0.552×10⁻³ g/cm²] for an exposure time of 432 h.     

铝合金材料腐蚀损伤的声发射评价

为了研究如何利用声发射(AE)技术监测飞机主结构件的腐蚀损伤从而为确定飞机日历寿命提供科学依据。首先介绍了航空铝合金材料在加速腐蚀过程中的AE信号特征,说明如何利用AE技术来监测腐蚀损伤,进而讨论如何对材料的安全性能和剩余寿命进行评估。试验表明, AE能比超声和涡流等常规无损检测方法更早地发现铝合金材料的腐蚀损伤。通过研究加速腐蚀过程中腐蚀损伤程度及腐蚀AE信号随加速腐蚀时间的变化规律,获得了腐蚀损伤与AE参数之间的变化关系。说明AE技术可用于探测早期腐蚀、研究腐蚀发展规律及监测和评估腐蚀损伤方面。     

腐蚀声发射信号降噪方法

为了从复杂背景噪声中有效地检测出腐蚀声发射信号,采用短时分形维数和离散分数余弦变换相结合的降噪方法,利用声发射检测系统,对6% FeCl₃·6H₂O溶液中Q235钢板的全面腐蚀和局部腐蚀声发射信号进行了降噪处理。实验结果表明,腐蚀声发射信号分别加入白噪声、有色噪声和粉红噪声,在输入信噪比为0~15dB的条件下,此方法降噪效果与标准离散余弦、离散分数余弦变换方法相比,输出信噪比最高可提升8 dB。所述降噪方法对检测腐蚀声发射信号以及对金属剩余寿命的评价具有一定意义。      

高强度钢手工焊接后过程的声发射实时监测研究

本针对实际工艺中使用的高强度钢，重点对手工焊接的冷却过程利用声发射技术进行实时监测。本次试验是和先前在不同型号的钢板在手工焊接过程中所产生的声发射信号进行比较的基础上进行的，主要目的是寻找高强度钢在手工焊接的冷却中所产生的活性裂纹在冷却阶段的声信号特征。     

Detection of stress corrosion cracking of high-strength steel used in prestressed concrete structures by acoustic emission technique

The stress corrosion cracking (SCC) of high-strength steel used in prestressed concrete structures was studied by acoustic emission technique (AE). A simulated concrete pore (SCP) solution at high-alkaline (pH ≈ 12) contaminated by sulphate, chloride, and thiocyanate ions was used. The evolution of the acoustic activity recorded during the tests shows the presence of several stages related respectively to cracks initiation due to the local corrosion imposed by corrosives species, cracks propagation and steel failure. Microscopic examinations pointed out that the wires exhibited a brittle fracture mode. The cracking was found to propagate in the transgranular mode. The role of corrosives species and hydrogen in the rupture mechanism of high-strength steel was also investigated. This study shows promising results for an potential use in situ of AE for real-time health monitoring of eutectoid steel cables used in prestressed concrete structures.     

Trapping and release of rare gases by 304L stainless steel

Helium andargon ions in the energy range 100 to 1400 eV and at doses varying from 10¹² to 10¹⁵ ions/cm² were implanted in a 304L stainless steel sample. Following implantation a linear temperature increase of the sample caused the gases to be released. The thermal release rates were studied as a function of ion dose and energy. The maxima observed in the thermal release rates are used to determine activation energies for thermally activated processes occurring in the metal. A rapid increase in the CO release rate coincident with the highest temperature He re-emission maximum indicates that the same mechanism is responsible for the release of both CO and He. It is suggested that the transport mechanisms revealed here are important in controlling void formations in neutron irradiated metals.     

Oxidation of AISI 304L stainless steel surface with atomic oxygen

Oxidation of stainless steel surface in oxygen atmosphere was investigated by Auger electron spectroscopy (AES) depth profiling. The samples made of AISI 304L stainless steel were exposed to highly non-equilibrium oxygen atmosphere at different temperatures between 300 and 800 K and for different periods between 5 and 600 s. The degree of dissociation of oxygen molecules was of the order of 10%. A thin oxide layer formed on the stainless steel surface consisted of the iron oxide. The thickness depended on the sample temperature. At room temperature it was 7 nm, and it remained the same up to 200 °C. With further increase of temperature, the thickness of the oxide layer increased and reached 40 nm at 450 °C. The thickness was independent of exposure time. The results were explained by two mechanisms of oxide growth. Up to 200 °C the oxidation was run by electro-migration, while at higher temperatures the thermal induced migration prevailed.     

基于声发射的光学元件损伤监测方法研究

光学元件损伤是限制激光通量水平提高的重要因素之一。为快速、准确地检测光学元件损伤是否产生,支撑光学元件循环修复策略的使用,研究并提出了基于声发射技术的光学元件损伤检测方法,通过研究光学元件损伤产生的声发射信号特征,判断光学元件是否发生损伤,使用一种基于二次相关和相关峰精确插值（FICP）的时延估计算法,通过仿真验证了该算法的可行性,结合时差定位原理建立了损伤位置求解方法,并通过实验进行了验证。研究结果表明:该方法能从监测信号中快速地获得损伤的位置估计,其平均定位误差为8.61 mm,计算时间为0.143 s/次,对大口径光学元件的损伤在线监测具有应用潜力。     

基于光纤传输的结构损伤声发射监测系统研究

摘要：声发射检测技术作为一种先进的故障诊断技术,在大型起重设备检测行业“大行其道”。由于生产现场的环境比较复杂,不可避免地要受到各种噪声的影响。当前对声发射信号大多是靠电缆进行传输,这种传输方式有传输距离有限、信号容易受到干扰等缺点。针对传统电缆传输信号的不足之处提出使用光纤作为传输信号的媒介,设计并开发了一种基于光纤的声发射监测的信号采集系统,能够实现远程监测且信号的抗干扰能力比较好。     

The influence of implanted yttrium on the cyclic oxidation behaviour of 304 stainless steel

High-temperature alloys are frequently used in power plants, gasification systems, petrochemical industry, combustion processes and in aerospace applications. Depending on the application, materials are subjected to corrosive atmospheres and thermal cycling. In the present work, thermal cycling was carried out in order to study the influence of implanted yttrium on the oxide scale adherence on 304 steel specimens oxidised in air at 1273 K. In situ X-ray diffraction indicates that the oxides formed at 1273 K are different on blank specimens compared to implanted specimens. Glancing angle XRD allows to analyse the oxide scale composition after cooling to room temperature.Experimental results show that yttrium implantation at a nominal dose of 10¹⁷ ions cm⁻² does not improve significantly the cyclic oxidation behaviour of the austenitic AISI 304 steel. However, it appears that yttrium implantation remarkably enhance the oxidation resistance during isothermal oxidation. It reduces the transient oxidation stage and the parabolic oxidation rate constant by one order of magnitude.     

Hydrogen damage in AISI 304 stainless steel studied by Doppler broadening

Hydrogen damage of AISI 304 stainless steel has been systemically investigated by measuring Doppler broadening of positron annihilation. Defect profiles of the S-parameter, the low-momentum annihilation fraction as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) have been analyzed. Experimental results show that hydrogen damage between the surface and the bulk has a significant variation with depth, and strongly depends on the condition of hydrogen-charging, i.e. current density and charging time. It has been suggested that the increase in S-parameter near the surface after hydrogen-charging mainly comes from the formation of voids; however the increase in S-parameter in the bulk after hydrogen-charging mainly comes from the production of structural defects (dislocations). Defect densities induced due to hydrogen-charging in some cases (e.g. dislocation density in the bulk) are estimated based on the simple two-state trapping model.