纯钛循环变形孪晶的形貌

采用透射电子显微镜学和光学显微镜观察高纯钛单晶及工业纯钛循环变形过程中形成的孪晶，证实了孪晶是纯钛循变形的一种重要方式，几乎在所有位向的拉伸时钛单晶中都有孪生发生，工业纯钛在应变幅低于１．０％下循环变形时孪晶的生成和，在高应变幅高１．５％，随循环变形周次的增加，孪晶分数增加，利用自动图像分析分析仪首次建立了工业纯钛中的形变享晶分数与应变幅，循环周次的定量关系。     

工业纯钛低温拉伸和循环变形中的孪生行为

在-196℃下对钛进行了拉伸和低周循环变形,观察分析了变形后试样的微观组织.结果表明,工业纯钛在-196℃拉伸变形后,强度比在室温下拉伸变形有了明显的提高,塑性也有明显的增加;在-196℃下循环变形时,循环应力-应变曲线位于-196℃静拉伸应力-应变曲线的上方,显示出明显的循环硬化特征.微观组织观察表明,-196℃拉伸及循环变形试样中存在着大量的孪晶,且孪晶数量随着循环应变幅及循环周次的增加而增加.在工业纯钛-196℃下的拉伸及循环变形中孪生起重要作用.     

工业纯钛的低温拉伸行为研究

研究了工业纯钛TA2在-196℃到25℃时的拉伸性能及塑性变形机制。结果表明,随着温度的降低,TA2屈服强度和抗拉强度逐渐升高,断后伸长率先升高后降低,在-140℃达到最大值,断面收缩率逐渐升高,在-80℃达到79%后保持稳定。25℃、-80℃、-120℃、-196℃拉伸试样中均观察到孪晶、高密度位错、变形组织。25℃时,拉伸试样中孪晶极少。-80℃、-120℃、-196℃时孪晶数量大幅度增加,且不同温度拉伸样品中孪晶形态差异很大。25℃时,TA2拉伸过程中塑形变形为滑移主导,随着温度降低,挛生在拉伸塑性变形过程中发挥的作用逐渐增大。     

应用加工硬化率研究工业纯钛动态再结晶行为

为研究工业纯钛的动态再结晶行为,利用Gleebe实验机对工业纯钛在变形温度为700,800,900和950℃及应变速率为0.01,0.1,1和5s-1的条件下进行热模拟压缩实验。应用加工硬化率对实验得到的应力-应变数据进行处理,结合变形后材料微观组织的分析,求得工业纯钛的动态再结晶临界条件。结果表明,工业纯钛在热变形过程中发生了回复与再结晶;发生动态再结晶时,再结晶临界应变随温度的升高及变形速率的降低而减小。将lnθ-ε曲线的拐点处对应的应变作为材料的再结晶临界应变是合理的,工业纯钛动态再结晶临界应变εc与峰值应变εp之间满足εc=0.485εp。     

高能喷丸表层纳米化对纯钛旋转弯曲疲劳性能的影响

采用高能喷丸方法使工业纯钛疲劳试样的表层实现纳米化,并进行了疲劳试验。结果表明,高能喷丸后其表层组织发生严重塑性变形并实现组织纳米化,是提高弯曲疲劳寿命的主要原因。扫描电子显微镜分析发现,疲劳裂纹源的位置主要呈现为表层和次表层两种情况。在相同应力水平下,疲劳裂纹源在次表层时疲劳寿命较长,而疲劳裂纹源在表面时疲劳寿命很短,相应的疲劳试样的表面损伤也比较严重。     

工业纯钛电子背散射衍射试样的制备

电子背散射衍射（EBsD）是一种较新的用来分析多晶体显微结构和组织的扫描电子显微镜技术,其试样的制备对其成像质量至关重要。通过对工业纯钛EBSD试样制备经验的总结,介绍了工业纯钛EBSD试样制备过程中切割、磨制、机械抛光、离子刻蚀和电解抛光等关键操作．提出了在EBSD试样制备过程中应注意的事项和技术要点。     

工业纯钛电子背散射衍射试样的制备

电子背散射衍射(EBSD)是一种较新的用来分析多晶体显微结构和组织的扫描电子显微镜技术,其试样的制备对其成像质量至关重要。通过对工业纯钛EBSD试样制备经验的总结,介绍了工业纯钛EBSD试样制备过程中切割、磨制、机械抛光、离子刻蚀和电解抛光等关键操作,提出了在EBSD试样制备过程中应注意的事项和技术要点。     

室温90°模具ECAP变形工业纯钛的力学性能

采用两通道夹角Φ=90°,外圆角Ψ=20°的模具,在室温,以C方式(两次挤压道次之间试样绕纵轴旋转180°)对工业纯钛进行了4道次ECAP(Equal Channel Angular Pressing)变形,成功制得表面光滑无裂纹试样,并对其力学性能和微观组织进行了检测分析.结果表明,工业纯钛经室温4道次ECAP变形后,原始晶粒细化到170 nm左右,显微维氏硬度和抗拉强度分别由1 792 MPa、438 MPa提高到2 486 MPa、728 MPa,且保持良好的塑性,断后伸长率为21.4%.     

工业纯钛TA1的高温摩擦与磨损行为

工业纯钛(TA1)表面塑性剪切抗力较低且氧化膜保护作用有限,在滑动摩擦时会产生严重的磨损行为。经高温氧化处理的TA1圆盘试样通过高温摩擦磨损试验机以及扫描电镜(SEM)和能谱(EDS)分析,研究实验温度、氧化膜及富氧α层对TA1摩擦磨损行为的影响规律。结果表明,由于磨屑的润滑作用,在相同的载荷和磨损时间下,有氧化层TA1的摩擦因数范围在0.07~0.3,无氧化层TA1摩擦因数范围在0.55~0.9之间。摩擦磨损实验温度越高,有氧化层的TA1摩擦处的犁沟形貌分布越多、越深。对于无氧化层TA1试样,随温度升高和对磨时间的延长,裂纹更易扩展形成剥层磨损。TA1材料的主要磨损方式为剥层磨损、黏着磨损以及氧化磨损,无氧化膜及富氧α层的TA1材料黏着磨损更为严重。表面硬度和磨损机制不同造成高温下摩擦磨损性能的差异。     

工业纯钛TA1的金相制样方法

针对工业纯钛TA1的金相制样方法进行了研究,对比了机械抛光和电解抛光两种方法的抛光效果,得到了机械抛光和电解抛光的最佳工艺参数。结果表明:经4次机械抛光+化学侵蚀,或在高氯酸+冰醋酸(体积比6∶94)电解液中60V电压下电解抛光14s,均可得到无变形孪晶的显微组织;但电解抛光相比机械抛光时间更短,效率更高,得到的显微组织形貌图质量也更好。     

EFFECT OF STRESS-STRAIN BEHAVIOR ON LOW-CYCLE FATIGUE OF α-β TITANIUM ALLOYS

Tensile specimens of Ti-6A1-4V with four levels of interstitial oxygen content and a Ti-8Al-1Mo-1V alloy with different heat treatments to alter grain size and/or microstructural character are subjected to slow strain-controlled cyclic deformation leading to rupture in the 5-500 cycle range. Indication of crack initiation as well as rupture life are compared, relative to the plastic excursion strain. On this basis, the effects of grain size and oxygen content are not clearly discriminated. Yet, some of the materials exhibit markedly superior performance. This improvement seems to be related to a characteristic evolution in the shape of the cyclic stress-strain curve. Here, relative to a full convex hysteresis loop of early cycles, the later cycles exhibit a reduced stress level, or cyclic softening, in the first half of the excursion, followed by a resurgence of strength to initial stress levels in the latter portion. The enhanced strain hardening rate enabling this terminal strength restoration is thought to stabilize the deformation, reducing the amount of stress-relaxation-induced tensile strain. Taking such strain as an increment of damage in a cumulative cyclic creep strain criterion provides a correlation between the evolving shape of the cyclic stress-strain curve and the low cycle fatigue endurance. Results indicate the absolute increase in the terminal plastic strain hardening rate to be a constant of a material, independent of the cyclic strain excursion.     

MECHANISTICALLY BASED MODELS FOR THE PREDICTION OF FATIGUE DAMAGE IN A BETA TITANIUM ALLOY

This paper presents the results of recent studies of the micromechanisms of room temperature fatigue damage elucidated in a metastable beta Ti15V3Cr3Al3Sn alloy. The fatigue damage mechanisms observed include: grain boundary sliding, crack initiation/propagation, and crack coalescence prior to the onset of catastrophic failure. Mechanistically based models are presented for the prediction of fatigue damage (plasticity and cracking). The models are based on fracture mechanics idealizations of the complex damage modes observed during fatigue experiments, in which acoustic emission signals were collected from deformed sections. Following appropriate noise filtration and careful analysis of the detected acoustic emission signals, the number of counts due to cracking is shown to represent a scalar measure of damage. A modified power law expression (modified Paris law) is also proposed to describe the relationship between the cracking count rate and the effective stress intensity factor. Estimates of the fatigue lives are obtained by integrating between appropriate limits, after the separation of variables in the modified Paris law expression. The measured and predicted fatigue lives were generally in good agreement.     

FACTORS CONTROLLING THE FATIGUE STRENGTH OF NITRIDED TITANIUM

Abstract— The factors affecting the fatigue strength of nitrided titanium were clarified. The fatigue strength depended strongly on the fracture strength of the compound layer formed on the surface by nitriding. We found a Hall-Petch relationship between the fatigue strength of nitrided titanium and the grain size. The findings indicated that the reduction in the fatigue strength by nitriding results from both the formation of the compound layer possessing low fracture strength and grain growth occurring from ordinary nitriding. Furthermore, low-temperature nitriding (620°C, 24 h) was proposed to suppress grain growth. This treatment method improved not only the wear resistance and the corrosion resistance but also the fatigue strength of titanium.     

高级写字楼空调与二次装修

对高级写字楼的租户特点以及由二次装修引起空调效果不佳的原因进行分析,并对此类建筑的空调设计提出改进建议.     

带中心孔的钛合金扩散连接层合板裂纹扩展特性

为了研究含孔TC4钛合金扩散连接层合板的裂纹扩展行为,进行了含ϕ6中心孔的8mm厚单层板材、三层(3+2+3)扩散连接层合板和三层(3+2+3)含ϕ12止焊区扩散连接层合板的疲劳对比试验,试验中施加标识载荷,通过断口判读裂纹形态和尺寸,得到裂纹扩展(a,N)数据,建立了裂纹扩展da/dN-a曲线,对单层板、层合板和止焊层合板的裂纹扩展行为和规律进行了对比。结果表明：单层板出现规则的半椭圆形孔壁裂纹;层合板由于存在层合界面的影响,出现不规则的半椭圆孔壁裂纹;而止焊层合板以角裂纹为主,裂纹扩展过程分为三阶段;三类试件的da/dN-a曲线可用双对数线性关系描述;三层板的裂纹扩展特性不弱于单层板;止焊层合板的裂纹扩展性能有明显改善,提高了含孔层板的损伤容限特性。     

A STUDY OF SHORT FATIGUE CRACK GROWTH BEHAVIOUR IN TITANIUM ALLOY IMI 685

Abstract— The fatigue growth of short cracks in coarse grained IMI 685, having an aligned a microstructure, has been monitored using a two stage replication technique. Crack growth rates are presented in terms of the failure mechanism and compared with standard data obtained from through cracked, compact tension specimens. The maximum difference, of up to four orders of magnitude, between long and short crack growth rates is associated with separation along specific crystallographic planes resulting in a cleavage-like fracture appearance. The rate of short crack growth is also shown to be dependent on applied stress and a dwell at maximum load during the fatigue cycle.     

DEVELOPMENT OF FATIGUE CRACKING IN AIRCRAFT ENGINE COMPRESSOR DISKS OF TITANIUM ALLOY Ti–6Al–3Mo–2Cr

Fractographic features related to fatigue growth in a titanium alloy Ti–6Al–3Mo–2Cr were examined in compressor disks that had failed in service. In-flight block cyclic loading that included hold-time loading and variable amplitudes of vibrational loading produced fracture characteristics which mainly reflected the two-phase (α + β) lamellar structure of the titanium alloy and contained localized areas of fatigue striations.
Blocks of cyclic loads which included cycles of hold-time loading during the testing of disks resulted mainly in the formation of fatigue striations with no evidence of the lamellar microstructure of the titanium alloy. An analytical equation Vi = [(1 − ν2 )/(16 π E σ_{0.2 )][Ke ]2i} is suggested to describe the relationship between the crack propagation rate, V, and the equivalent stress intensity factor, K_e , as applied to the semi- and then to the quarter-elliptical-shaped cracks. Fractographic features are discussed and the disks' fatigue crack growth behaviour over 50 flights is demonstrated.     

快凝钛合金中硅化物的析出及长大规律

研究了热处理对Ｔｉ－５Ａｌ－０．３Ｓｉ和Ｔｉ－５ＡＩ－２Ｚｒ－０．３Ｓｉ（质量分数，ｍｇ／ｇ）析出相长大规律的影响结果表明，含硅的钛合金的快凝态和在６００℃短期（１ｈ）处理后的基体中无析出相＞６５０℃时，近球状的相大量析出热处理后析出相聚集长大速度很快．Ｔｉ－５Ａｌ－０．３Ｓｉ的析出相为四方的Ｔｉ３Ｓｉ，其长大激活能为２１９ｋＪ·ｍｏｌ－１．加入Ｚｒ后，分布更加弥散且长大速度更快的（Ｔｉ，Ｚｒ）６Ｓｉ３的长大激活能为１０５ｋＪ．ｍｏｌ－１