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研究了Ti-6Al-4V ELI合金板材的显微组织对疲劳裂纹扩展速率的影响.用金相显微镜对不同热处理制度下该合金α和β转变组织的变化进行了观察分析.采用MTS-810低周疲劳试验机测试合金的裂纹扩展速率.通过Origin 6.0软件对数据进行处理并绘制裂纹扩展速率(△a/△N)与应力强度因子幅△K的关系曲线.结果表明:在Pairs区范围内,疲劳裂纹扩展速率对双态组织中初生α相含量的多少不敏感,而在近门槛区和快速扩展区,裂纹扩展速率对组织比较敏感;在本实验研究的条件下,细针编织状魏氏组织的da/dN<平直状片层组织的da/dN<双态组织的da/dN. 相似文献
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TA5钛合金的疲劳裂纹扩展门槛值与疲劳裂纹扩展速率的关系 总被引:3,自引:0,他引:3
研究了大规格TA5钛合金热轧环村的疲劳裂纹扩展门槛值ΔK_(th)与疲劳裂纹扩展速率加da/dN之间的关系。结果表明,Δk_(th)值可由近门槛区的da/dN表达式直接按定义da/dN值算,而无需进行繁琐的试验测定。这一结果同样适用于β区加热热轧TA5钛合金板材。 相似文献
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为了研究TB6钛合金自然萌生小裂纹的扩展行为,针对单边缺口拉伸试样开展室温下不同应力比(R=0.1,0.5)的小裂纹扩展实验,采用复型法观测了小裂纹的萌生与扩展情况。结果表明:同一应力比下,随着应力等级的降低,小裂纹的萌生寿命由占全寿命的60%增加到80%,但应力等级对TB6钛合金小裂纹扩展速率没有明显影响。裂纹早期扩展速率受微观组织的影响大,TB6钛合金扩展速率转变临界值是200μm,一旦裂纹长度达到200μm,裂纹扩展速率将不受取向不同的晶界或晶粒影响而迅速提升。TB6钛合金疲劳小裂纹起源于试样缺口根部,所有试样的裂纹大部分为角裂纹,疲劳小裂纹萌生寿命占全寿命的绝大部分。 相似文献
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Ti-6Al-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6Ak-4V alloy has beeninvestigated by the uniaxial hot isothermal compression tests and a series of dilatometric experiments were also carried out todetermine the transformation temperatures at different cooling rates. Specimens for hot compression tests were homogenizedat 1050℃ for 10 min and then quickly cooled to different straining temperatures from 1050 to 850℃. Cooling rates were chosenfast enough to prevent high temperature transformation during cooling. Compression tests were conducted at temperaturesfrom 1050 to 850℃ in steps of 50℃ at constant true strain rates of 10~(-3) or 10~(-2) s~(-1). The apparent activation energy forcompression in two-phase region was calculated 420 kJ·mol~(-1). Partial globularization of cr phase was observed in the specimendeformed at low strain rates and at temperatures near the transformation zone and annealed after deformation. 相似文献
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针对目前金属材料疲劳裂纹扩展门槛值测定中存在的测定周期长、试样尺寸较大以及单位周次裂纹扩展长度测量误差较大等问题,采用扫描电镜原位观察技术测定了TC4钛合金的疲劳裂纹扩展门槛值,即通过扫描电镜对裂纹扩展长度的实时精确测定实现快速获得材料的疲劳裂纹扩展门槛值。结果表明:利用该方法测得的TC4钛合金的疲劳裂纹扩展门槛值与已报道的数据基本一致,并且具有快速简便等优点,表明该方法可以用来测定金属材料的疲劳裂纹扩展门槛值。 相似文献
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采用光学显微镜研究了Ti-6Al-4V合金经超塑成形/扩散连接(SPF/DB)热影响后的微观组织演变,在室温和空气条件下进行了旋转弯曲疲劳试验,并采用扫描电子显微镜对试样断口形貌进行了观察.结果表明:Ti-6Al-4V合金经历SPF/DB热工艺后,初始的双态组织转变为了等轴组织;强度有所降低,塑性略有提高,而旋转弯曲疲劳极限从420 MPa降低至405 MPa,在相同应力条件下(σ=431 MPa),SPF/DB后试样的疲劳寿命从107量级降低至106量级;疲劳断口源区附近的放射线增粗且变的不连贯,疲劳裂纹扩展区的疲劳条带间距增大,裂纹扩展速率提高.这主要是由于SPF/DB热环境使Ti-6Al-4V合金片层α数量显著减少,降低了晶界总体长度,减弱了α相晶界对疲劳小裂纹扩展的阻碍作用. 相似文献
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对TC4-DT损伤容限型钛合金在150℃,25℃下的疲劳裂纹扩展速率da/dN进行了测试,给出了扩展速率和应力强度因子幅值△K之间的关系曲线.用SEM对2种温度下断口形貌进行了观测,实验结果表明,150℃的疲劳裂纹扩展速率试样具有较低的疲劳裂纹扩展速率,25℃的疲劳裂纹扩展速率试样具有较低的门槛值;稳态扩展区解理断裂和条带循环机制共存,150℃的da/dN试样中的疲劳辉间距比25℃试样细;快速扩展区的断口形貌呈韧窝型静载断裂特征,150℃的da/dN试样中的韧窝比25℃试样深. 相似文献
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Fretting fatigue tests of Ti‐6Al‐4V on Ti‐6Al‐4V have been conducted to determine the influence of stress amplitude and mean stress on life. The stress ratio was varied from R=−1 to 0.8. Both flat and cylindrical contacts were studied using a bridge‐type fretting fatigue test apparatus operating either in the partial slip or mixed fretting regimes. The fretting fatigue lives were correlated to a Walker equivalent stress relation. The influence of mean stress on fretting fatigue crack initiation, characterized by the value of the Walker exponent, is smaller compared with plain fatigue. The fretting fatigue knockdown factor based on the Walker equivalent stress is 4. Formation of fretting cracks is primarily associated with the tangential force amplitude at the contact interface. A simple fretting fatigue crack initiation metric that is based on the strength of the singular stress field at the edge of contact is evaluated. The metric has the advantage in that it is neither dependent on the coefficient of friction nor the location of the stick/slip boundary, both of which are often difficult to define with certainty a priori. 相似文献
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目的 揭示应力比对增材制造TC4钛合金疲劳裂纹扩展行为的影响规律。方法 采用紧凑型拉伸试样,在恒载荷幅条件下对激光增材制造TC4钛合金进行了应力比为0.1、0.3和0.5的疲劳裂纹扩展实验,定量评价了不同应力比下合金的疲劳裂纹扩展速率和变化规律。基于Paris公式对裂纹扩展速率进行了拟合,分析了应力比对各参数的影响规律。最后通过扫描电镜对断口表面形貌进行了观察,分析了应力比对断裂模型的影响。结果 在相同的?K条件下,疲劳裂纹扩展速率随着应力比的增大而增大。在Paris公式中,参数C随应力比的增大而减小,参数m随应力比的增大而增大,并且m和lg C呈现线性关系。随应力比的增大,断口表面的河流花样增多、疲劳辉纹变浅、二次裂纹数量增加。结论 应力比引起的裂纹尖端闭合效应和平面应力比变化是导致裂纹扩展速率发生改变的主要原因。 相似文献
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This paper presents the results of an investiga-tion of the effect of hydrogen treatment onmicrostructures and tensile and low cycle fatigueproperties of a Ti-6Al-4V cast alloy.The phasetransformation and the refining mechanism of thecast microstructure during the process of hydrogentreatment were studied.It was found that afterhydrogen treatment,the coarse Widmanstttenstructure of the as-cast Ti alloy was transformedinto a very fine and equiaxed α+β microstructurewithout any GBα phase.The tensile strength andductility and the low cycle fatigue life of thehydrogen treated specimens were significantly im-proved. 相似文献
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P. J. GOLDEN T. NICHOLAS 《Fatigue & Fracture of Engineering Materials & Structures》2005,28(12):1169-1175
The objective of this work was to compare the fretting fatigue performance of Ti‐6Al‐4V dovetail specimens on Ti‐6Al‐4V pads having various contact angles typical of engine hardware; 35°, 45° and 55° dovetail angles were considered. The dovetail fixtures were instrumented with strain gages so that the local normal and shear contact forces could be calculated. The contact force hysteresis loops were recorded showing the stick‐slip history. At R= 0.1, gross slip was observed for several thousand cycles followed by partial slip after the average coefficient of friction increased. At R= 0.5, gross slip was present only during the first half cycle. During partial slip, the slope of the shear versus normal force was a function of the dovetail angle. The local contact loads, therefore, differed for the same remotely applied force. Despite this, the fretting fatigue life depended primarily on the remotely applied load not dovetail angle. 相似文献
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目的 探究选区激光熔化技术工艺参数线间距对钛合金Ti–6Al–4V增材试件力学性能的影响。方法 通过SLM成形技术,以钛合金粉末为原材料、以线间距为变量制备增材成形试件,通过拉伸试验、断口形貌分析以及表面硬度测量获取不同线间距工艺参数条件下钛合金成形试件力学性能表现较好的较优解。结果不同线间距条件下成形试件拉伸曲线差异较大,线间距为0.05mm和0.10mm时,成形试件拉伸曲线表现较好,成形试件断口组织撕裂均具有连续性,韧窝结构明显,具有一定塑性。试件成形过程受氧化影响,其拉伸性能与硬度性能表现不一致。结论 试验最终工艺参数如下:曝光时间为80μs、点间距为40μm、线间距为0.05mm,SLM成形试件获得了较高的表面硬度,试件断口组织撕裂连续性较为明显,韧窝结构较大,断口界面缺陷较少,力学性能较优。 相似文献
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Ling Ren ;Zheng Ma ;Mei Li ;Yu Zhang ;Weiqiang Liu ;Zhenhua Liao ;Ke Yang 《材料科学技术学报》2014,30(7):699-705
Surgical implant-associated bacterial infection is becoming a serious clinical problem.A series of copper-bearing titanium alloy,Ti—6AI—4V—xCu(x = 1,3,5 wt%),were fabricated in the present study in order to reduce the hazard of the bacterial infection problem by means of the strong antibacterial ability of Cu element.The metallography,X-ray diffraction,antibacterial ability,corrosion resistance and cytotoxicity of Ti—6AI—4V—xCu alloys were preliminarily studied with comparison to the commercial medical Ti—6AI—4V alloy.The Ti—6AI—4V—xCu alloys showed obvious antibacterial abilities with good corrosion resistance and cytocompatibility,and the antibacterial role was enhanced with increasing Cu content,which has significant potential for clinical applications as surgical implant materials. 相似文献
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Yong LIU Jingchuan ZHU Zhongda YIN Mingwei LI School of Materials Science Engineering Harbin Institute of Technology Harbin China 《材料科学技术学报》2004,20(3):292-294
The effect of triple annealing on stress relaxation of Ti-6Al-4V alloy as well as the microstructure after stress relaxation werestudied. The results showed that triple annealing treatment enhanced the resistance of stress relaxation performance, andwhen the temperature was rising, this effect became notable. The stress relaxation deformation mechanism is of dislocationcreep at 400℃ and recovery creep at 600℃. 相似文献
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采用TiZrNiCu合金作为中间层材料研究了Ti3Al基合金与Ti-6Al-4V合金的瞬间液相(TLP)扩散连接接头成分、组织转变及显微硬度.研究结果表明,连接温度和连接时间对接头成分和组织有较大的影响.随着连接温度的提高和连接时间的延长,接头中元素分布趋于均匀,连接区宽度增大.连接温度为850℃和900℃时,液相的残留使得接头中存在Ti-Cu金属间化合物.当连接温度为950℃,连接时间为30min时,等温凝固的完成使Ti-Cu金属间化合物从接头中消失.随着连接温度的提高和连接时间的延长,接头连接区硬度降低.当连接温度为950℃,连接时间为30min时,接头硬度分布较均匀. 相似文献