Interfacial fatigue crack propagation in Ni-base superalloy protective coatings

It is important to control the interface strength of coatings and composite materials; a feature that has been noted for many years. However, how can interface strength be evaluated and controlled? In order to explore this aspect, subcritical fatigue crack growth behaviour was investigated along the interface of a CoNiCrAlY coated Ni‐Base superalloy. According to the traditional fatigue test methodology, fatigue crack propagation tests were carried out, using double cantilever beam specimens. The resistance to the fatigue crack propagation was successfully evaluated by a fracture mechanics approach. Particular attention was given to the effects of surface finish of the substrate as a coating parameter, the test temperature, and long‐term thermal ageing after the coating.     

Effect of high-temperature protective coatings on fatigue lives of nickel-based superalloys

This study concerns MCrAlY coatings (M is Ni, Co or both) sprayed by a vacuum plasma spraying process for protection against high-temperature corrosion and oxidation of gas turbine components, such as turbine blades and duct segments. The effect of high-temperature protective coatings on fatigue lives of nickel-based superalloys were investigated at high temperature under push–pull loading and rotary bending and then compared with uncoated superalloys, such as equiaxed IN738LC, unidirectional solidified CM247LC and single-crystal CMSX-2. The high-cycle fatigue lives of MCrAlY-coated superalloys at high temperature under push–pull loading showed an inferior performance when compared with the uncoated superalloys. This was because the crack initiation site was different. The high-cycle fatigue cracks of nickel-based superalloys initiated at casting cavities which were exposed on the specimen surface, whereas the high-cycle fatigue cracks of MCrAlY-coated specimens initiated at interface defects, such as small pores and grid residue, between the MCrAlY coating and the substrate and grew into the MCrAlY coating, and then into the substrate. Similarly, the rotary bending fatigue properties of MCrAlY-coated superalloys at high temperature showed an inferior performance when compared with the uncoated superalloys. This is because of a high stress due to the higher Young's modulus of the MCrAlY coating (in comparison with the substrate) being induced at the MCrAlY coating surface. The crack initiation site was on the specimen surface in both cases of the nickel-based superalloys and the MCrAlY-coated superalloys, respectively. As a result, it was considered that, for rotary bending tests, the fatigue life reduction was due to the high stress that originated from the difference of elastic constants between the MCrAlY coating and the superalloy. Consequently, in fatigue life design it is necessary to take account of the stress levels in a coating layer.     

GH4133合金热机械疲劳寿命的预测

通过对典型的热机械疲劳寿命预测模型的分析,结合GH4133合金的热机械疲劳损伤特性,建立了热机械疲劳寿命预测模型－－新的损伤分数模型,用该模型预测了GH4133合金在571－823℃的热机械疲劳寿命,结果表明,新的寿命预测模型不仅简便,而且预测精度较高。     

新型Ni-Cr-Co基高温合金长期时效后的相分析

采用物理化学相分析技术研究了一种新型Ni Cr Co基高温合金长期时效后的析出相γ′(+η),M23C6,MC和M6C(+μ)的相组成,分析了时效温度和时效时间对析出相含量的影响,并用X射线小角散射(SAXS)分析了γ′(+η)相在不同粒度间隔的质量分布。     

全导流95-Ⅱ型塔板上液层温度分布与板效率

引　言塔板是塔器中传质、传热最重要的元件之一 .近几十年来 ,开发大通量、高效率、低压降、低能耗的新型塔板一直是人们努力的方向 .在综合分析已有各种塔板结构性能的基础上 ,通过热力学熵增速率分析法[1] ,张志炳等开发出了 95 Ⅰ型大通量塔板[2 ] ,有关该塔板的详细介绍见文献 [3].为了进一步提高塔板效率 ,本文提出了一种全导流 95 Ⅱ型塔板结构 ,并对其进行性能实验 ,以得到板上液层的温度分布与板效率值 ,并且与 95 Ⅰ型塔板的板效率值进行了比较 .1　实验部分1 1　 95 Ⅱ型塔板结构及其全导流板的设置95 Ⅱ型塔板的平面结构如…     

Windows 95下的直流驱动器通讯程序设计

CONTROL TECHNIQUES公司MENTOR II系列直流调速单元在很多行业获得应用,文章介绍运行在Windows 95环境的主机利用串行接口和直流驱动器的通讯程序设计。     

Crack growth behavior of SRR99 single crystal superalloy under thermal fatigue

The thermal fatigue behavior of a single crystal superalloy SRR99 was investigated.Specimens with V-type notch were tested at the peak temperatures of 900,1000,and 1100℃.The crack growth curves as a function of the number of cycles were plotted.With the increase of peak temperature,the crack initiation life was shortened dramatically.Through optical microscopy (OM) and scanning electron microscopy (SEM) observation,it was found that multiple small cracks nucleated at the notch tip region but only one or two of them continued to develop in the following thermal cycles.The primary cracks generally propagated along a preferential direction.Microstructure changes after thermal fatigue were also discussed on the basis of SEM observation.     

应变速率对电场处理GH4199合金拉伸变形行为的影响

研究了电场处理后的长期时效GH4199合金在不同应变速率下的拉伸变形行为.结果表明,随应变速率增加合金屈服强度升高,应变速率低于3.3×100 s-1时,应变速率敏感指数m值较低且随应变速率的增加无明显变化;当应变速率超过3.3×100 s-1时,m显著升高,当应变速率为3.3×101 s-1时,m达到0.16;随应变速率增加合金拉伸塑性呈下降趋势;在较低应变速率范围内变形时,电场处理后产生的退火孪晶是改善合金塑性的主要因素,随着应变速率的提高,晶内开动的滑移系数量增加,塑性变形能力随之提高,但存在于合金晶界处的连续分布的碳化物对晶界的弱化作用逐渐显露,晶界与晶内塑性变形能力差异增大,晶界成为断裂的主要途径,导致合金塑性降低.     

热处理态NiCoCrAlY涂层的抗中性盐雾腐蚀性能

通过500 h中性盐雾试验研究了在低膨胀高温合金GH907上低压等离子喷涂(LPPS)的NiCoCrAlY涂层在热处理后的抗腐蚀性能,并与热处理态的LPPS制备的NiCr涂层的抗腐蚀性能进行了对比.结果表明,盐雾腐蚀500 h后,NiCoCrAlY涂层在扫描电镜下可以看到几个无破坏性作用的腐蚀坑,涂层表面仍保持较好的完整性和光洁性,对腐蚀产物的EDS面扫描表明腐蚀产物主要为Al的氧化物,涂层的腐蚀保护等级仅下降到9级;而NiCr涂层的表面出现了较多的腐蚀斑点,涂层的完整性和均匀性均已经被破坏,涂层表面产生了腐蚀裂纹,其腐蚀等级下降到4级.EDS分析表明腐蚀产物主要为Ni、Fe、Co等的氧化物.对比结果表明,NiCoCrAlY涂层表现出比NiCr涂层更强的抗中性盐雾腐蚀性能.     

一种定向凝固镍基高温合金的高温低周疲劳行为

本文研究了一种定向凝固镍基高温合金的高温低周疲劳行为。结合对合金微观变形结构的观察,分析了温度、应变保持时间对合金低周疲劳性能的影响。结果表明,温度对合金的变形有着明显影响,在760℃以下合金呈现循环硬化,而在850℃和980℃时则表现为循环软化,这是由于合金在不同温度范围内具有不同的微观变形机制。在应变峰值、应变谷值以及同时在应变峰值和谷值分别引入保持时间后,合金的高温低周疲劳寿命均有一定程度的降低。