稀土Ce对Al-Cu4.5%合金热疲劳性能的影响

在接近材料实际工况的实验条件下,以铝铜合金(Cu4.5%)为研究对象,用自约束型热疲劳实验机对铈加入量不同的合金,进行了热疲劳实验以及热疲劳裂纹萌生及扩展规律的研究。结果表明:在裂纹萌生阶段,不加铈的铝铜合金的裂纹萌生速度明显大于加铈的合金;在裂纹扩展阶段,不加铈的铝铜合金裂纹扩展速度仍是最快。加入0.5?的合金在裂纹形成后期扩展速度明显加快,这是因为合金中出现针状富稀土相,这种针状相割裂了基体,使得合金力学性能降低、热疲劳抗力下降。加入0.3?的合金不论在裂纹萌生阶段还是裂纹扩展阶段,其热疲劳抗力都优于其它成分的合金。     

先进镍基高温合金疲劳损伤的微观机制

通过对FGH96粉末高温合金、DZ125定向凝固高温合金、DD6单晶高温合金大量疲劳断口的断裂特征进行统计分析,研究了这3类镍基高温合金疲劳损伤的微观机制。结果表明,这3类合金疲劳断裂的宏观形貌有较大的区别,但由于这几类合金均为镍基面心立方晶体结构,因此其疲劳损伤断裂具有相同的微观演变规律和断裂机制,即:从疲劳裂纹的萌生至裂纹的快速扩展均是以滑移机制进行;疲劳扩展第1阶段均为类解理特征,疲劳扩展第2阶段为疲劳条带,快速扩展区呈现为滑移面、滑移台阶、韧窝特征。由于其组织和成形工艺的区别,其共同的特征表现的具体形貌有所区别。     

Al2O3sf/ZL109复合材料的热疲劳短裂纹的扩展行为

在室温至２８０℃间热循环条件下,研究了体积百分含量１８％的氧化铝短纤维增强ＺＬ１０９铝－硅合金复合材料和基体ＺＬ１０９铝－硅合金的热军短裂纹扩展行为,并且探讨和复皮劳裂纹的形成机制和扩展过程。研究结果显示,短裂纹扩展阶段,热疲劳裂纹与增强体纤维有明显的交互作用,但复合材料的皮劳短裂纹扩展速率比基体合金的大,加强基体与纤维的界面结合,提高纤维质量,可望提高复合材料的热疲劳裂纹扩展抗力。     

Ce对2090Al-Li合金疲劳裂纹扩展行为的影响SCIEI

研究了7075,2090和2090+Ce合金的疲劳裂纹扩展行为。2090合金的名义疲劳裂纹扩展抗力优于7075合金,归因于其高的裂纹闭合效应,但其本征疲劳裂纹扩展抗力低于7075合金。在2090合金中添加微量Ce,可同时提高其本征疲劳裂纹扩展抗力和裂纹闭合效应,故其名义疲劳裂纹扩展抗力大幅度提高。     

GH4742合金疲劳裂纹扩展行为

研究GH4742合金在室温、700℃及750℃的疲劳裂纹扩展行为。分析温度和应力强度因子对疲劳裂纹扩展寿命与速率的影响,利用扫描电镜观察不同温度下的疲劳裂纹扩展断口。采用背散射电子衍射(EBSD)技术分析合金裂纹扩展的晶体学机制。结果表明,随着温度的升高,合金的裂纹扩展寿命降低,裂纹扩展速率增加,沿晶断裂特征更明显。应力强度因子越大,裂纹扩展速率越大。在原始大变形晶粒中裂纹以穿晶方式沿着小角度晶界扩展,裂纹扩展到再结晶晶界时以沿晶扩展为主,其扩展方式取决于相邻晶粒的面间角和取向差。     

GH4698合金的疲劳裂纹扩展行为

对GH4698合金在室温、650及750℃的裂纹扩展行为进行研究,讨论温度对裂纹扩展寿命与速率的影响,观察不同温度下的裂纹扩展断口。采用背散射电子衍射(EBSD)技术对合金裂纹扩展的晶体学机制进行分析。结果表明,随着温度的升高,合金的裂纹扩展寿命降低,裂纹扩展速率增加,断裂模式由室温下穿晶断裂为主转变为高温下的沿晶断裂为主;裂纹附近应变程度较大,且小角度晶界密度较高。     

GH625和GH536变形高温合金焊接的疲劳裂纹扩展速率分析

测定GH625和GH536变形高温合金在室温下的疲劳裂纹扩展速率,分析合金疲劳裂纹扩展速率与断口特征以及微观组织的关系。结果表明:应力强度因子幅ΔK较小时GH625合金焊缝处的疲劳裂纹扩展速率小于母材,ΔK较大时焊缝处的疲劳裂纹扩展速率较快;在裂纹稳定扩展阶段,GH536合金热影响区的疲劳裂纹扩展速率大于母材;GH625和GH536合金母材断口裂纹扩展区可见明显的疲劳条带特征,而焊缝中心裂纹扩展区以类解理特征为主;GH625和GH536合金焊接部位的疲劳裂纹扩展速率的快慢受焊缝或热影响区内部的析出物影响较大。     

高铌TiAl合金双态组织室温断裂行为研究

通过对高铌TiAl合金双态组织的缺口试样进行原位拉伸、相应的断裂表面SEM观察,研究其拉伸断裂机制和裂纹扩展的动态过程.结果表明,高铌TiAl合金双态组织的断裂模式主要是穿晶解理断裂;合金的断裂过程是主裂纹首先起裂,微裂纹的产生、扩展和连接主裂纹,直至断裂;在裂纹扩展过程中,尖端附近区域范围内的γ相晶粒内易形成微裂纹,为其断裂过程的一个明显特征;对于双态缺口试样,由于晶粒细小,缺口根部出现应力集中,裂纹扩展路径比较平直.     

镍基单晶合金高温低周疲劳微观损伤及断裂机制

通过开展低周疲劳试验,研究了镍基单晶高温合金DD6的疲劳微观损伤及断裂机制。结果表明:低温条件下DD6表现为起始硬化,饱和,然后软化至断裂,高温时试样则表现为起始软化。低应变下高温可降低单晶合金疲劳性能。低温下试样循环硬化程度比高温时高,高温下原子热激活行为降低了材料形变抗力。试样裂纹萌生位置有两种:一种在试样表面,另一种在晶体内部微孔处。裂纹扩展具有两个阶段:初始阶段扩展面非常平坦,仅有小量撕裂棱;扩展阶段则产生河流状花纹,扩展区内以疲劳辉纹形式扩展,最终进入瞬断区。     

应力比对Mg-3Al-2Sc合金疲劳行为的影响

在不同应力比条件下对热挤压变形的Mg-3Al-2Sc合金进行了疲劳试验,分析了应力比对合金裂纹扩展行为和断裂机制的影响。结果表明:在应力幅Δσ=60 MPa时,随应力比的增加,Mg-3Al-2Sc合金疲劳寿命显著降低,裂纹扩展速率提高。在裂纹萌生区和扩展区疲劳断裂机制主要表现为解理断裂,而在瞬断区主要表现为准解理和沿晶断裂的复合断裂机制。     

氢对LC4高强铝合金应力腐蚀断裂的影响

采用慢应变速率拉伸试验研究了氢在LC4高强铝合金应力腐蚀断裂过程中的作用。结果表明，LC4合金在干燥空气中不发生应力腐蚀断裂，而在潮温空气中发生应力腐蚀断裂，在潮湿空气和阳极极化条件下，铝合金的应力腐蚀断裂机理是以阳极溶解为主，氢几乎不起作用，在预渗氢或阴极极化条件下，氢脆起主要作用，预渗氢时间延长可加速LC4合金的应力腐蚀断裂。     

Effect of Strength and Microstructure on Stress Corrosion Cracking Behavior and Mechanism of X80 Pipeline Steel in High pH Carbonate/Bicarbonate Solution

The stress corrosion cracking (SCC) behaviors and mechanisms of X80 pipeline steels with different strength and microstructure in high pH carbonate/bicarbonate solution were investigated by slow strain rate testing and electrochemical test. The results showed that the cracking mode of low strength X80 steel composed of bulky polygonal ferrite and granular bainite in high pH solution was intergranular (IGSCC), and the SCC mechanism was anodic dissolution (AD). While the mixed cracking mode of high strength X80 steel consisted of fine acicular ferrite and granular bainite was intergranular (IGSCC) in the early stage, and transgranular (TGSCC) in the later stage. The decrease of pH value of crack tip was probably the key reason for the occurrence of TGSCC. The SCC mechanism may be a mixed mode of AD and hydrogen embrittlement (HE), and the HE mechanism may play a significant role in the deep crack propagation at the later stage. The cracking modes and SCC mechanisms of the two X80 steels were associated with its microstructure and strength.     

Mechanismus des Rißwachstums bei der Spannungsrißkorrosion des austenitischen Stahls X6 CrNiTi 18 10 in wäßriger Chloridlösung bei erhöhten Temperaturen

SCC crack growth mechanism of austenitic stainless steel X6 CrNiTi 18 10 in aqueous chloride solution at elevated temperatures The SCC crack growth mechanism of steam generator heat transfer tubes from stainless steel X6 CrNiTi 18 10 under internal stress conditions at elevated temperatures is discussed. Based on crack tip characterization by means of Scanning and Transmission Electron Microscopy and the evidence of hydrogen originated throughout the corrosion process a crack propagation model is presented. The results refer to a microcrack induced gradual crack growth caused by local hydrogen embrittlement. Microcrack growth has been observed due to slip-band decohesion. The crack growth rate is mainly influenced by the stress state near the crack tip and the hydrogen evolution throughout the corrosion process.     

The susceptibility of 90Cu-10Ni alloy to stress corrosion cracking in seawater polluted by sulfide ions

Electrochemical polarization measurements and slow strain rate tests (SSRT) of a 90Cu-10Ni alloy in highly sulfide polluted seawater were conducted to investigate stress-corrosion cracking (SCC) behavior. The severity of the SCC depends on the sulfide concentration in the seawater. The severity increases as the concentration increases. Because the major time in SCC is spent in the initiation process of the propagating crack, the fracture toughness has only a minor effect in the component life failed by SCC. The SCC behavior of CDA706 is strictly linked to sulfide concentration in the range of 100 to 1000 ppm. The general corrosion of Cu-Ni alloys in low (<100 ppm) and high (>100 ppm) sulfide polluted seawater increases due to the selective copper dissolution. Cyclic polarization measurements confirmed that the corrosion rate decreases slightly as the sulfide concentration increases. Pitting tendency was high in the low concentration range of sulfide and low in the high concentration range. The presence of stresses in SCC removes the protective layer as it increases during testing of the specimen or during the actual service of a component. The authors propose that film rupture occurred, and two proposed SCC mechanisms were operational, namely sulfide stress cracking associated with the anodic dissolution in the low sulfide concentration range and hydrogen embrittlement, which was dominant in the high sulfide concentration range. It was found that a synergism exists between sulfide and stress that enhances the effect of the latter.     

Kinetics and mechanism of crack growth during stress corrosion cracking of zirconium alloys

Using the electroresistivity method the influence was investigated of the anodic and cathodic polarization on the crack growth rate during stress corrosion cracking (SCC) of Zr alloys in aqueous and nonaqueous electrolytes. The ambiguous effect of the cathodic polarization on CGR was observed. The role of local dissolution and hydrogen embrittlement by SCC of Zr alloys has been discussed in terms of the previously developed method of identification of the SCC mechanism.     

航空航天铝合金腐蚀疲劳研究进展

铝合金因具有高的比强度、比模量,好的加工性能及焊接性能,在航空航天领域应用广泛.而腐蚀疲劳是造成航空航天材料失效的重要原因之一,因其危害性高、破坏性强且难以提前预测等特点,受到了广泛关注.铝合金腐蚀疲劳问题一直是飞机日历寿命研究中的重点问题,随着可重复使用航天器理念的提出,多次空天往返和地面修复过程也使腐蚀疲劳问题在可重用航天器上不可忽视.综述了近年来航空航天铝合金腐蚀疲劳的研究现状,从航空铝合金腐蚀疲劳机理的角度,归纳了腐蚀疲劳裂纹萌生和扩展机制.从腐蚀疲劳环境模拟和腐蚀环境等效两方面,介绍了目前主要的实验室腐蚀疲劳试验技术.分别从材料因素、环境因素和力学因素,分析对腐蚀疲劳裂纹扩展及寿命的影响.重点关注了腐蚀疲劳交替形式下疲劳寿命的特点.提出了在多因素共同影响下的腐蚀疲劳裂纹扩展、损伤演化和寿命预测,以及加速腐蚀环境的当量等效.试验与模拟的有机结合,是今后铝合金腐蚀疲劳的重要发展方向.     

超高强度钢37SiMnCrNiMoV应力腐蚀过程中声发射信号的研究

采用AE技术对超高强度钢37SiMnCrNiMoV在3.5%NaCl 溶液中的SCC行为进行研究.证明在裂纹的稳定扩展区内,裂纹是间歇,跳跃式的扩展.发现 腐蚀裂纹尖端的应力强度因子处于0.7KIC和0.23KIC时,平均每次声发射事件 对应的裂纹扩展量相近;应力强度因子处于035 KIC时,平均每次声发射事件对应 的裂纹扩展量较大;声发射事件的发生频率随应力水平的增加,有很大的增加.腐蚀裂纹扩 展的全过程存在两种不同的声发射信号.还证明了37SiMnCrNiMoV的应力腐蚀裂纹扩展过程 中,氢脆起着主要的作用.提出了计算腐蚀裂纹稳定扩展区内声发射事件累积数的公式.     

时效制度对Al-Zn-Mg-Cu铝合金应力腐蚀敏感性的影响

采用恒载荷拉伸应力腐蚀试样、恒变形C环应力腐蚀试样以及预裂纹双悬臂(DCB)试样,对不同时效制度处理的7B04预拉伸厚板的应力腐蚀性能进行测 定,并进行了扫描电镜断口形貌分析.研究表明,其抗应力腐蚀性能与时效制度密切相关,从峰值时效T6状态到过时效T74、T73状态,应力腐蚀敏感性依次降低.预拉伸厚板T6状态的应力腐蚀门槛值为120 MPa,而T74状态的应力腐蚀门槛值为300 MPa.T74状态的应力腐蚀开裂应力强度因子KISCC是T6的近2倍,且应力腐蚀裂纹扩展速率(da/dt)也明显降低.T6状态和T74状态的7B04铝合金应力腐蚀断裂为沿晶断裂,并有二次裂纹.而T73状态的断口形貌无典型的应力腐蚀沿晶断裂特征,为孔洞腐蚀特征,而且其KISCC几乎接近KIC.这说明T73状态的7B04铝合金几乎没有应力腐蚀敏感性.     

Die Ausbreitung von Spannungskorrosionsrissen in der Aluminium-Legierung AlZnMg 3

Crack propagation during stress corrosion cracking of AlZnMg 3 alloy The authors have studied crack propagation in notched specimens exposed to sodium chloride solution at 30°C under constant load. Crack propagation have been followed by microphotography which has enabled gliding phenomena within the specimen to be followed, too. Starting from the rest potential and shifting it toward more cathodic values crack propagation is at first slowed down which is a type of cathodic protection, but afterwards – in the hydrogen evolution region with simultaneous cathodic corrosion – the crack propagation velocity increases. This fact can be attributed to hydrogen embrittlement. Taking into account that the industrial alloy is more resistant than the high purity alloy one may arrive at the conclusion that the impurity content acts as a decelerating factor giving rise to an extension of the incubation period.     

LC-4铝合金应力腐蚀裂纹内的电化学行为

本文提出了一种测定应力腐蚀裂纹内的电位和 pH 值的方法。这种方法适用于应力腐蚀裂纹内和各种腐蚀缝隙内的电化学测试。设备简单,操作方便而且精确度高。文中列出用该法测定 LC-4铝合金应力腐蚀裂纹尖端处微区的电化学数据,并结合电位 pH 图进行了讨论和分析。作者根据所得结果提出由微电池相互耦合而成的多电极体系等效电路模型,可以较好地解释本文的实验结果。对于 LC-4铝合金,裂纹尖端电位与 pH 值间存在下列关系=-0.750-0.043pH(SCE)而在 Pourbaix 图中则穿过钝化区,并与应力腐蚀敏感性存在对应关系。