The use of XPS, FTIR, SEM/EDX, contact angle, and AFM in the characterization of coatings

Coatings are applied to surfaces for a variety of reasons: to enhance their appearance, to protect the substrate, to augment the adhesion to other layers, or to functionalize them for further reactions. To evaluate the efficacy of the coating, it is often necessary to analyze the substrate and the coating to ensure that the needed characteristics are present. To this end, the use of x-ray photoelectron spectroscopy (XPS), contact angle, and atomic force microscopy (AFM) can provide information about the surface composition, its morphology, and its ability to be wetted with various solvents. Scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) and Fourier transform infrared spectroscopy (FTIR) can provide a clear picture of the near surface components as well as the continuity of coatings. All of these aspects are valuable in evaluating a coating and essential when problems are encountered. The application of these techniques to the analysis of coatings is discussed.     

铝合金自冲铆接头疲劳性能及失效机理

自冲铆是轻量化材料的有效连接技术,为促进该技术的广泛应用,文中基于两组铝合金自冲铆接头,采用疲劳测试、统计方法、断口分析和X-射线能谱仪元素分析,获得接头疲劳特性和断口典型部位微观组织特征,从而对铝合金自冲铆接头疲劳性能及失效机理进行研究。结果表明,随着疲劳载荷降低,接头疲劳寿命稳定性和相对滑移量下降。由于多铆钉接头有效减小了应力集中,其疲劳强度比单铆钉接头提高了31.36%~23.14%,且多铆钉接头的疲劳寿命稳定性较高。多铆钉接头中存在首要和次要承载顺序,疲劳断裂表面为首要承载顺序所在位置。接头疲劳宏观失效模式均为下板断裂,疲劳裂纹主要萌生于铆钉管腿与下板接触部位,微振磨损区域自铆钉管腿底部向铆钉头方向生长。减缓该部位的摩擦作用,可有效延迟疲劳裂纹萌生和减缓裂纹扩展,从而提高接头疲劳寿命。     

Delamination during drilling in polyurethane foam composite sandwich structures

The objective of this paper is to study the influence of drilling velocity, feed rate, and flank length on the delamination of polyurethane foam sandwich structures. A Taguchi-based design of experiments was used to assess the importance of the drilling parameters, and scanning electron microscopy (SEM) was used to assess the damage from drilling. The drilling of sandwich structures results in significant damage caused by delamination and surface roughness around the drilled holes. The drilling process was evaluated based on a factor called the delamination factor, which is defined as the ratio of the maximum diameter of the damage zone, measured using SEM, to the standard hole diameter (drill diameter). Analysis of variance of the experimental results showed that cutting speed was the most significant parameter among the controllable parameters during drilling of sandwich specimens followed by flank length and feed rate. Finally, confirmation tests were performed to make a comparison between the experimental results and the correlation results. The damage mechanisms are explained using SEM.     

马氏体轴承钢碳氮共渗滚动接触疲劳失效机理EI北大核心CSCD

碳氮共渗工艺应用广泛,但对碳氮共渗后零部件的滚动接触疲劳失效机理研究较少。采用气体碳氮共渗对马氏体轴承钢进行表面改性处理,对碳氮共渗试样进行滚动接触疲劳试验,研究碳氮共渗对轴承钢滚动接触疲劳性能的影响及其失效机理。研究结果表明:碳氮共渗试样表面硬度、残余应力和残余奥氏体含量显著提高,使得其接触疲劳寿命明显高于常规试样。疲劳裂纹萌生于表面和亚表面,其中大量表面平行裂纹主要由表面白色蚀刻层硬度梯度变化而导致,表面材料受到严重微观塑性变形产生晶粒细化;亚表面裂纹萌生位置受最大应力的分布和渗层厚度的影响。表面和亚表面疲劳裂纹的扩展和连接最终导致碳氮共渗试样出现浅层剥落和分层剥落的失效形貌。     

齿轮疲劳失效分析与工艺参数优化

齿轮传动在航空、机械、冶金、交通运输等领域中得到了广泛的应用,齿轮构件的疲劳失效会导致整个传动系统的失效。为了确保齿轮运行的平稳性和可靠性,对20CrMnTi渗碳齿轮的工艺参数进行优化。先对齿轮常见的齿根弯曲疲劳和齿面接触疲劳进行详细的失效机理分析,并基于此利用田口方法设计齿轮疲劳正交试验,然后根据设计参数进行齿轮疲劳试验,利用Minitab软件对试验数据进行分析。结果表明：影响齿轮疲劳性能的因素等级排序分别是渗碳层深度、心部硬度和表面粗糙度,且渗碳层深度的影响程度远大于后两者。     

天然橡胶/顺丁橡胶共混物疲劳历程的研究

采用扫描电子显微镜、电性能测定和热重法等分析手段，研究了炭黑补强的天然橡胶／顺丁橡胶共混硫化胶的疲劳历程，探索了其内在的疲劳损伤机理。     

疲劳损伤定量分析与失效评估研究进展

本文对疲劳损伤定量分析的理论和模型、断口定量分析疲劳寿命、疲劳应力以及对工程构件安全使用具有重要意义的基于损伤容限设计思想的原始疲劳质量与失效评估技术的研究现状进行了分析.通过断口定量反推疲劳应力和疲劳寿命应用最多的是Paris公式,疲劳裂纹萌生寿命目前还无法直接从断口上反推出来,一般通过人为设定a0值的方法计算疲劳裂纹萌生寿命.相对而言,国外对在役构件的剩余寿命评估方面开展了较多的工作.本文分析比较了国内外在疲劳损伤定量分析与失效评估研究的侧重点和思路的异同,并指出了加强失效分析在产品设计、生产、使用和维护各个环节的应用力度及开展失效评估技术研究是失效分析领域发展的两个重要方向.     

TC17钛合金电子束焊接接头的疲劳裂纹扩展规律及疲劳剩余寿命

首先通过试验取得母材及焊接接头的疲劳裂纹扩展速率,然后结合TC17钛合金电子束焊接接头CTOD试验结果及裂纹容限计算值,以估算其疲劳剩余寿命.结果表明:在低应力水平或低△K下,TC17电子束焊缝的da/dN数据与母材的基本相当;然而随着应力水平的增加,焊缝的da/dN值越来越大.在初始裂纹尺寸相同的情况下,TC17合金电子束焊缝与母材疲劳裂纹扩展寿命曲线存在交叉点.当应力幅大于交叉点应力幅时,TC17母材疲劳裂纹扩展到临界裂纹尺寸的剩余寿命要高于相应焊缝的剩余寿命;当应力幅小于交叉点应力幅时,TC17母材扩展到临界裂纹尺寸的剩余寿命要低于相应焊缝的剩余寿命.     

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。     

先进的电子断层扫描技术在材料科学中的发展——基于透射电子显微镜和扫描透射电子显微镜(英文)

介绍了基于透射电子显微镜和扫描透射电子显微镜的电子断层扫描技术在材料科学领域的最新进展。详细地描述各种电子断层扫描的类型:基于透射电子显微镜的断层扫描技术包括明场断层扫描、暗场断层扫描、弱束暗场断层扫描、环形暗场断层扫描和能量过滤断层扫描;基于扫描透射电子显微镜的断层扫描技术包括高角环形暗场断层扫描、环形暗场断层扫描,非共格明场断层扫描、电子能量损失谱断层扫描和X射线能谱断层扫描。报道了优化的倾转系列,比如双轴倾转、同轴倾转、锥形倾转以及等斜率倾转等。总结了先进的重构算法包括离散迭代重构技术、压缩传感算法以及等斜率算法。最后,提出了电子断层扫描技术在材料科学中的发展趋势。     

Study on Contact Fatigue Life and Failure Mechanism of Subquenched 42CrMo Steel

The effect of undissolved ferrite amount in subcritically quenched 42CrMo steel on contact fatigue properties and failure mechanism were studied. The amount of undissolved ferrite in the steel were 0%,3%,10%,15% and 20% in volume fraction, respectively. The experimental results show that the existence of undissolved ferrite can increase the contact fatigue life The contact fatigue life can be prolonged with increasing the amounts of undissolved ferrite The grain size can be fined by using subcritical quenching process and the area of phase boundaries can also be greatly increased. The stress relaxation and grain refinement due to occurring of plastic deformation are main reasons for improving the fatigue life. The existence of undissolved ferrite can increase the crack initiation period. Under the experiment conditions, when the amount of undissolved ferrite is 10%, the longest contact fatigue life can be the obtained.     

棘轮离合器疲劳裂纹原因分析

棘轮离合器是超越离合器的一种,具有尺寸小、重量轻、承载能力高、传动平稳、寿命长、啮合可靠性高的特点,在航空发动机传动系统中应用十分广泛。本研究分析了发动机起动不成功的故障现象,根据故障树分析方法查找故障原因,阐述了棘轮离合器工作原理,详细分析了故障产生的原因。结果表明：发动机起动不成功的主要原因是双速传动机构失效,棘爪疲劳裂纹是导致双速传动机构失效的主要原因,棘爪产生疲劳裂纹是棘爪存在制造缺陷和S含量超标,提出了改进方法和预防措施,对发动机的修理具有参考价值。     

零件失效分析和抗疲劳设计

简单介绍了零件失效分析的作用及基本任务,指出疲劳失效是零件失效的主要形式之一.阐述了金属疲劳失效的外因和内因,并总结了三种典型的疲劳分析方法,以及如何在工程中使用这些方法.最后,详细论述了一体化疲劳耐久性工程的基本理念及其在产品开发中的作用,还概括性介绍了所涉及的一些主要工作任务,包括寿命目标的确定、数据采集、载荷分析...     

拖拉机二轴齿轮接触疲劳损坏的研究

针对拖拉机生产企业存在的零件生产质最问题,系统分析了拖拉机中央传动系统二轴18CrMnTi钢齿轮接触疲劳损坏的原因、类型、特征和形成机理,并进一步研究了齿轮接触疲劳损坏的影响因素,为生产企业采取针对性措施,改善二轴齿轮加工工艺提供了帮助.     

Study of microstructure and corrosion kinetic of steel guitar strings in artificial sweat solution

Corrosion processes of strings on musical instruments occur frequently. Such processes significantly influence sound quality, but also human health because metals may provoke skin allergy. Therefore, in this study the corrosion process of six guitar strings and metal ions release associated with nickel allergy was monitored after immersion in sweat solution for 28 days. Dissolution of metal ions was measured as a function of time, and the changes of the samples after 28 days were studied by SEM/EDS. The results have shown that the amounts of dissolved metal ions in corrosive solution are decreasing in the following order: Fe³⁺ < Sn²⁺ < Mn²⁺ < Si⁴⁺ < Ni²⁺. The corrosion of electric guitar strings in artificial sweat solution was determined by the solubility of samples. The electric guitar strings E6, A5 and D4 corrosion kinetic in artificial sweat followed parabolic rate relation, while g3, h2 and e1 strings followed linear rate relation. After the 4 weeks of monitoring, the quantities of the nickel eluted ions did not exceed the limits prescribed by standard regulations. Therefore, such items do not present a threat to human health.     

840D车轮辐板孔疲劳失效及裂纹容限研究

通过裂纹和断口的观察、理化检验、模拟仿真及其力学计算,分析了840D车轮辐板孔裂纹的特征、机理和原因.结果表明:裂纹属于高低周复合机械疲劳,裂纹主要在制动加机械载荷工况下萌生和扩展.统计分析确定了裂纹扩展速率,结合裂纹发展形态和理论计算给出了临界裂纹长度,进而评估出裂纹容限为20mm.     

关于两起工程机械设备早期疲劳失效的分析及探讨

通过宏观分析、扫描电镜、光学显微镜等手段对装载机车架及液压挖掘机的液压泵驱动轴的早期断裂进行了综合分析,结果表明均为制造工艺不当而诱发的疲劳断裂失效,同时对有关防范措施作了探讨。     

Cavitation and grain boundary sliding during creep of Mg-Y-Nd-Zn-Mn alloy

Creep of squeeze-cast Mg-3Y-2Nd-1Zn-1Mn alloy was investigated at the constant load in the stress range of 30-80 MPa. Tensile creep tests were performed at 300℃up to the final fracture.Several tests at 50 MPa were interrupted after reaching the steady state creep;and another set of creep tests was interrupted after the onset of ternary creep.Fraction of cavitated dendritic boundaries was evaluated using optical microscopy.Measurement of grain boundary sliding by observation of the offset of marker lines ...     

Study on Fatigue Properties of Turbine Disk Groove Modeling Specimens of GH4720 Alloy

基于航空发动机涡轮盘榫槽结构特点及其工作状态,采用榫槽模拟件对GH4720合金的疲劳失效机理和裂纹扩展寿命进行了实验研究和理论分析。研究结果表明:GH4720合金榫槽模拟件的疲劳失效表现为3个阶段:(i)模拟涡轮盘榫槽处由于较高的应力集中而产生滑移,进而萌生裂纹;(ii)随着应力集中和循环载荷的持续,相邻晶粒间位错开动、发生滑移,裂纹在晶粒间传递;(iii)随着应力强度因子范围增大,剪应力和主应力交互作用、滑移系开动及位错在不同滑移系间的运动,裂纹快速扩展。在实验基础上建立了GH4720合金的疲劳裂纹扩展寿命模型,基于有限元分析的榫槽处的应力和裂纹扩展寿命模型得到的裂纹扩展寿命与实验结果相符,表明该裂纹扩展寿命模型可用于工程中预测涡轮盘的剩余寿命。