Ta,Nb氧化膜破裂的临界应力的测量及其影响因素的研究

<正> 本工作将测量金属氧化膜应力的单面氧化弯曲法和检测氧化膜破裂的声发射技术相结合,创新性建立了金属氧化膜开裂临界应力的测量装置。首先用对照实验说明了声发射系统检测氧化膜破裂的灵敏性及所用波导的有效性,并阐明了试样表面光洁度、棱角和     

氧化铝膜的破裂行为

用声发射技术研究了Fe 2 3Cr 5Al 0 .2 1Ti合金在 110 0℃空气中氧化后的氧化膜破裂行为及离子注入1× 10 17Y /cm2 对氧化膜破裂行为的影响。实验结果表明 :随着氧化时间的增长 ,Fe 2 3Cr 5Al 0 .2 1Ti合金在冷却过程中氧化膜开始发生破裂的时间相同 ,表明氧化膜发生破裂的临界应力相同 ,但声发射累积计数增加 ,表明膜破裂程度加重。离子注入Y 后氧化膜发生破裂的时间延迟 ,表明膜发生破裂的临界应力增大 ,且声发射计数减少 ,表明膜破裂程度减小 ,氧化膜粘附性得到显著提高。     

声发射技术在氧化膜破裂监测中的应用

在高温腐蚀领域,声发射技术是一种最有效且具有极高灵敏度的监测氧化膜破裂的技术.通过分析声发射计数,可以判断氧化膜首次发生破裂的时间及最后破裂的程度.如对声发射频谱进行分析,则可以判别氧化膜内发生塑性变形、开裂及剥落的过程.利用声发射技术还可以测量氧化膜/合金界面处预存物理缺陷大小及分布.此外,将声发射技术与其它技术结合,可建立全新的分析测试系统.综述了声发射技术用于监测氧化膜破裂的原理和方法,以及多种性能测试方面的应用与新发展.     

MA956和Fecraloy两种合金氧化膜的断裂应变

利用四点弯曲／声发射方法在室温下测量了ＨＡ９５６和Ｆｅｃｒａｌｏｙ合金表面形成的氧化膜的断裂应变。结果表明，在张应力作用下，ＭＡ９５６合金在１０００℃、１１００℃和℃三种温度以下及Ｆｅｃｒａｌｏｙ合金在１２００℃下不同时间氧化后形成的膜的断裂应变几乎不变，分别约为０．３４％和０．１３％。这两种合金氧化时都主要形成Ａｌ２Ｏ３。ＭＡ９５６合金氧化膜在实验时间范围内从未发现有开裂，而Ｆｅｃｒａｌｏｙ合金     

钇离子注入改善Co—40Cr合金表面氧化膜粘附性的作用

用声发射（AcousticEmission）方法及扫描电镜SEM／EDXA,对Co－40Cr合金在1000℃空气中20h恒温氧化后表面氧化膜的开裂和剥落进行了研究．并与该合金表面离子注入3×1016Y ／cm2和3×1017Y ／cm2后的氧化结果进行了比较．结果表明,离子注钇后极大地改善了合金表面氧化膜的抗开裂和抗剥落性能．此外,用声发射方法能够间接地测量出氧化膜／合金界面处“预存缺陷”（pre-existingdefects）的分布情况．离子注钇改善合金表面氧化膜的粘附性与注钇后减小了界面处“预存缺陷”的数目及平均大小有关．     

膜致应力对应力腐蚀裂尖力学特性的影响

氧化膜破裂理论是目前定量预测核电高温水环境中镍基合金应力腐蚀开裂速率应用最为广泛的理论模型之一,其中应力强度因子是衡量应力腐蚀开裂速率的重要参量。为进一步了解氧化膜破裂机理及裂纹扩展驱动力特性,提出了膜致应力强度因子。为了深入了解膜致应力强度因子在 EAC 裂纹扩展过程中裂尖的力学状况,在不考虑外载的情况下,从理论和数值模拟两方面分析研究了EAC 裂尖基体金属区域的应力应变分布状态,得出了膜致应力强度因子对裂尖Mises应力、等效塑性应变、拉伸应力、拉伸应变及拉伸应变梯度的影响规律,为提高定量预测高温高压水环境中镍基合金及不锈钢 EAC 扩展速率精度奠定基础,进而完善了氧化膜破裂机理。     

DZ125合金抗高温氧化性能研究

研究了DZ125合金在1 100℃时的氧化行为,分析了该合金表面氧化膜的生成和失效机制。结果表明,1 100℃氧化30h后DZ125合金表面氧化膜呈分层结构,其中外层为Cr_2O_3,中间层为NiO及NiCr_2O_4,内层为Al_2O_3。DZ125合金在1 100℃空气中的氧化动力学满足抛物线规律。在氧化过程中,聚集于晶界区域的Hf、Ta等高活性元素会优先发生氧化,为O的向内扩散提供通道,造成合金的选择性内氧化,并且随着氧化时间延长,氧化膜在应力的作用下开裂,最终导致膜层剥落失效。     

钛合金5621S及含钕钛合金5621S氧化膜的应力

测量了含钕及不含钕两种钛合金5621S于600-800℃在氧气中氧化条件下氧化膜的生长应力和于800℃氧化不同时间后氧化膜的残余应力。通过氧化膜的生长应力、热应力、残余应力大小的比较,表明Ti5621S合金中添加钕能降低氧化膜的生长应力。含钕及不含钕两种钛合金氧化膜的生长应力和热应力同数量级。于冷却过程中若钛合金5621S氧化膜发生显著破裂,由于应力充分释放,其残余应力反较含钕的钛合金5621S氧化膜的低。     

膜致应力对应力腐蚀裂尖力学特性的影响（英文）

氧化膜破裂理论是目前定量预测核电高温水环境中镍基合金应力腐蚀开裂速率应用最为广泛的理论模型之一,其中应力强度因子是衡量应力腐蚀开裂速率的重要参量。为进一步了解氧化膜破裂机理及裂纹扩展驱动力特性,提出了膜致应力强度因子。为了深入了解膜致应力强度因子在EAC(环境致裂)裂纹扩展过程中裂尖的力学状况,在不考虑外载的情况下,从理论和数值模拟两方面分析研究了EAC裂尖基体金属区域的应力应变分布状态,得出了膜致应力强度因子对裂尖Mises应力、等效塑性应变、拉伸应力、拉伸应变及拉伸应变梯度的影响规律,为提高定量预测高温高压水环境中镍基合金及不锈钢EAC扩展速率精度奠定基础,进而完善了氧化膜破裂机理。     

合金元素钕对5621S钛合金氧化膜粘附性的影响及其作用机制

采用声发射技术研究了5621S及添加1％Nd的5621S钛合金,在700℃、800℃、850℃空气中所形成的氧化膜于冷却过程中的开裂和剥落。重点分析了含Nd合金所形成的复合氧化物“钉子”对氧化膜的粘附性的影响,“钉子”的存在对于膜内裂纹的扩展起着延长距离及阻碍作用。实验表明,含钕合金氧化膜的粘附性虽得到极大改善,而膜仍易于开裂。这是因为在冷却过程中,“钉子”受到大的压应力。如果“钉子”较大,就会成为萌生裂纹的起始点。文中还分析了裂纹产生机制。     

Stress analysis for the high-temperature gaseous corrosion of metal tubes

Stress analysis for the high-temperature gaseous corrosion of metal tubes is presented. The mechanical stresses arising from the difference in thermal expansion coefficients and volumes of a metal and its oxide can result in cracking of the oxide scale and in an increase of the oxidation rate. The model interprets the different behavior of oxide scale growths on outer versus inner tube surfaces. The oxidation behavior of tantalum tubes at temperatures of 825 °C and 930 °C is calculated based on this analysis. Results of the calculations are in good agreement with observed experimental data.     

高度稳定化β型阻燃钛合金Ti40的氧化和氧化层剥落机理

对高度稳定化β型阻燃钛合金Ti40的氧化机理和氧化层剥落机理进行研究表明：合金氧化增重随温度升高明显增加,至1050℃反而降低;600℃的氧化膜主要为TiO2和V2O5,高于700℃氧化,因V2O5的挥发,氧化膜主要为TiO2,随温度升高,氧化物晶粒粗化,氧化膜疏松多孔,与基体黏附性降低,不低于900℃时开裂和剥落,不低于800℃氧化,氧化层疏松还存在SiO化合物,温度升高,SiO数量增多,由圆形球变为星形,至1050℃随氧化层剥落而消失;剥落后的基体氧化层仍为疏松状,有不连续分布的Cr2O3膜存在,同时还分析了Ti40合金不抗氧化的原因及氧化机理,提出了氧化机理模型。在分析氧化膜内应力产生及内应力释放机制基础上,提出了Ti40合金氧化层开裂、剥落机理。     

氧化膜应力研究进展

综述了氧化膜应力产生与释放机理,重点介绍了氧化膜应力原位测试技术的新进展及稀土绎氧化膜和的影响,探讨了氧化膜应力研究的发展方向。     

Investigations for the Validation of the Defect Based Scale Failure Diagrams—Part I: Nickel Oxide

Mechanical stresses imposed on protective oxide scales can lead to cracking and failure of the scale and consequently to a loss of the protective properties. Therefore, an assessment of the mechanical stability limits is of great interest. In this work, a new concept using defect based oxide scale stability diagrams to assess the mechanical stability limits is discussed. In contrast to mechanical failure diagrams proposed earlier, the presented model is based on physical defect size instead of scale thickness. Nickel oxide scales on high purity (99.99 %) nickel were thermally grown in dry and humidified synthetic air to provide a model oxide system. SEM investigations were carried out to examine the physical defect structure in the oxide scales and mechanical 4-point bend testing was used to measure the critical strain for through scale cracking. The data served for establishing a data base for the validation of the defect based scale failure model.     

The significance of acoustic emission during stressing of TiAl-based alloys. Part I: Detection of cracking during loading up in tension

Samples of fully lamellar Ti44Al8Nb1B and Ti44Al4Nb4Hf0.2Si have been tested in tension at room temperature while they were interfaced to an acoustic emission system. The generation of acoustic signals, at stresses well below the 0.2% yield stress and at higher stresses, has been shown to be due to the formation of cracks within individual lamellar colonies. Data obtained in the micro-strain region in loading–unloading measurements confirmed that there is significant plastic flow at stresses 200 MPa below the 0.2% proof stress of 625 MPa, and it is inferred that this flow gives rise to the cracking. The mechanism whereby such cracking occurs and the possible influence of these cracks on subsequent fatigue behaviour are discussed.     

PROTECTION AND DAMAGE OF PREFORMED OXIDE SCALES OF Fe-25Cr-5Al AND-10Al ALLOYS DURING THEIR SUBSEQUENT SULFIDATION

ＰＲＯＴＥＣＴＩＯＮＡＮＤＤＡＭＡＧＥＯＦＰＲＥＦＯＲＭＥＤＯＸＩＤＥＳＣＡＬＥＳＯＦＦｅ－２５Ｃｒ－５ＡｌＡＮＤ－１０ＡｌＡＬＬＯＹＳＤＵＲＩＮＧＴＨＥＩＲＳＵＢＳＥＱＵＥＮＴＳＵＬＦＩＤＡＴＩＯＮ￥Ｑｉ，Ｈｕｉｂｉｎ；Ｚｈｕ，Ｒｉｚｈａｎｇ；Ｈｅ...     

水蒸气对NiCrAlY涂层抗高温氧化性能的影响

采用热重分析及现代表面分析方法研究了低压等离子喷涂Ni CrAlY涂层在纯氧以及含5%水蒸气的O2中的高温氧化行为,结果表明：在纯氧的氧化环境中 ,NiCrAlY涂层氧化动力学遵循抛物线规律,在含有5％的水蒸气的O2中,NiCrAlY涂层在氧 化至110 h后氧化动力学几乎呈直线规律.XRD及SEM分析显示,NiCrAlY涂层在O2中氧化180 h后,表面形成一层致密的Al2O3;而在含5%水蒸气的O2中氧化180 h后表面氧化层中 除了有Al2O3外,还有NiO和Cr2O3.其原因在于水蒸气中的氢在氧化物中的溶解,致 使Ni2+扩散 速度增加,使氧化层变得疏松,降低其抗氧化性.     

The isothermal oxidation behaviour of Fe-Cr-Al and Fe-Cr-Al-Y alloys at 1200°C

The isothermal oxidation kinetics of Fe-14Cr-4Al, Fe-27Cr-4Al and similar alloys containing 0.008, 0.023 and 0.8Y have been investigated in 1 atm. oxygen at 1200°C and related to the appropriate oxide morphologies and compositions. The yttrium-free alloys develop a convoluted oxide morphology, with significant areas of lost contact between the oxide and the alloy specimen surface, which results from lateral growth of the oxide and the development of high compressive growth stresses. These are due to oxide formation within the oxide where Al³⁺ ions diffusing outwards through the bulk oxide meet O^2? ions diffusing inwards along oxide grain boundaries. The additions of yttrium to the alloys reduce the oxide growth stresses and suppress the development of the convoluted oxide. This is reflected in the oxidation kinetics. During cooling, scale cracking and some spalling occurs for the yttrium-free alloys, due to the imposition of stresses, caused by the differential thermal contraction between the oxide and alloy, on the already highly stressed, partially detached oxide. Although the addition of 0.008Y to the alloy actually increases the amount of oxide spallation on cooling, further additions of 0.023Y or 0.8Y to the alloy reduce the oxide growth stresses, prevent scale detachment at temperature and thus reduce or prevent oxide damage on cooling.