焊后电子束局部热处理对GH4133合金接头疲劳性能的影响

针对涡轮盘材料GH4133合金，在电子束焊后采用新颖的电子束局部热处理工艺对接头进行热处理。通过700℃高温疲劳试验，研究了电子束局部热处理对电子束焊接接头疲劳寿命的影响，旨在为航空构件的电子束焊接及焊后电子束局部热处理加工积累性能数据和经验。     

7075铝合金电子束焊接温度场数值模拟

针对航空航天业中应用较广的7075铝合金,采用ANSYS有限元软件,按照划分单元、逐次计算并逼近真实值的近似计算方法,对该合金电子束焊接的热过程进行了计算机数值模拟的可行性研究.结果表明,7075铝合金电子束焊接过程中焊接热输入较大,焊缝较窄,熔深大.通过验证,用有限元数值模拟方法得到的焊接及热处理温度场分布规律与实测温度值基本一致.     

阳极电位下小幅载荷在腐蚀疲劳裂纹扩展中的作用

研究了A537钢在3.5%NaCl水溶液中,阳极溶解条件下以不同方式叠加在主载荷ΔP上的小幅载荷对疲劳裂纹扩展da/dN～ΔK曲线的影响,并与空气中的结果进行比较,讨论了阳极溶解影响小幅载荷行为的机理.结果表明:空气中幅度小于30%ΔP的小载荷叠加在主载荷底部时对裂纹扩展没有影响,而阳极溶解能使这些主载荷底部的小幅载荷对裂纹扩展过程产生重要作用,在阳极溶解条件下,即使是幅度为零的保持载荷(B0)对裂纹扩展也具有明显的加速作用;虽然阳极溶解对主载荷顶部的幅度为30%ΔP(T30)和70%ΔP(T70)的小载     

EFFECIS OF TEMPERATURE AND OVERLOAD RETARDATION ON CORROSION FATIGUE CRACK GROWTH OF HIGH STRENGTH STEEL

The fatigue crack growth rate (CGR) of ultra high strength steel 30CrMnSiNi2A in distilledwater at 18,35 and 55℃ were measured.It was confirmed that the temperature is strongly af-fected on the corrosion fatigue CGR of ultra high strength steel.An expression concerning theeffects of Δ K and temperature on the CGR was proposed.The fact that the apparentactivation energy (36.6 kJ/mol) resulted from regressive analysis of CGR data was similarto the activation energy of hydrogen diffusion in γ-Fe,strongly supporting the theory ofhydrogen-assisted crack growth.The overload retardation effect was greatly reduced in cor-rosion fatigue crack growth,especially at lower frequency,e.g.,0.1 Hz.This phenomenonmight be due to the increase of the SCC component of CGR after an overload.     

EFFECT OF NON-PROPORTIONAL OVERLOADING ON FATIGUE CRACK GROWTH

The effect of proportional and non-proportional overloading on mode l fatigue crack growthhave been studied,and the influences of crack tip plastic zone,crack tip blunting as well ascrack closure were discussed.Proportional(model I)overloading may cause more seriouscrack growth retardation than non-proportional(mixed mode)overloading.Therefore,forestimating the fatigue life of engineering structures to simplify a real overload which may of-ten be non-proportional as a proportional one is not always safe.     

电子束焊接深熔产生机理的研究现状与发展

综述了电子束焊接深熔产生机理的研究进展,从能量分配传热模型、空腔力学行为、熔深计算、电子束聚焦与深熔等方面简要归纳分析了电子束深熔过程产生机理的研究现状,解释了一些电子束焊接瞬态特征以及提出的各种有关电子束深熔焊接物理模型,并对电子束焊深熔机理需进一步开展的研究工作做了展望。     

残余压应力场中疲劳短裂纹扩展模型及实验

结合实验讨论了残余应力对裂纹扩展作用的模型及其存在的问题。指出用公式△Ｋｅｆｆ＝（Ｋｍａｘ＋λＫｒ）－Ｋｏｐ中较准确地计算出残余压应力场中裂纹的扩展速率。残余压应力既使裂纹闭合力提高，又使最大应力强度因子降低，两者均使裂纹扩展驱动力△Ｋｅｆｆ减少，因而降低了裂纹的扩展速率。     

高强度钢腐蚀疲劳裂纹扩展的温度效应和过载迟滞效应

通过在18,35和55℃蒸馏水中疲劳裂纹扩展试验,证明了超高强度钢30CrMnSiNi2A腐蚀疲劳具有强烈的温度效应,得到了ΔK值和温度对裂纹扩展速率影响的复合表达式。由于扩展速率数据拟合得到的表观激活能值(36.7kJ/mol)十分接近于氢在γ-Fe中的扩散激活能值,支持了氢助裂纹扩展的观点。对大气中疲劳裂纹扩展具有重要价值的过载迟滞效应,在腐蚀疲劳时显著地减小,在0.1Hz的低频率下尤其明显。     

力学失配对电子束焊接接头疲劳裂纹扩展行为的影响

研究了高温合金电子束焊接接头区的疲劳裂纹扩展行为,深入分析了接头区力学失配对疲劳裂纹扩展方向及疲劳裂纹扩展速率的影响规律。结果表明,由于力学不均匀性的影响,电子束焊接接头的疲劳裂纹扩展具有不稳定性,位于高匹配焊接区的疲劳裂纹偏离原裂纹扩展方向,跨越焊接区与母材,呈复合型扩展;焊接区疲劳裂纹的集团使得裂纹尖端有效应力强度因子减小,因而焊缝区裂尖局部有效裂纹扩展驱动力下降,导致接头的疲劳裂纹扩展速率下     

3.5%NaCl溶液对铝合金疲劳裂纹扩展特性的影响

对高强铝合金7050—T7451在模拟海水(3.5%NaCl溶液)的疲劳裂纹扩展特性进行了试验研究结果表明,3.5%NaCl溶液加速了7050—T7451铝合金的疲劳裂纹扩展速率da/dN.考虑应力比影响的有效应力强度因子面ΔKefT可以满意地表征不同环境中的的da/dN.裂纹面上的腐蚀产物较薄,对疲劳裂纹闭合的影响可以忽略不计.     

MICROFRACTOGRAPHY OF NEAR-THRESHOLD FATIGUE CRACK PROPAGATION IN DUAL-PHASE STEELS

SEM microfractography of near-threshold fatigue crack propagation were carried out in thedual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m).All of them are featured by cyclic cleavage characteristics in near-threshold region,i.e.,main-ly controlled by mode Ⅱ stress.In the higher ΔK regions,the fracture surfaces are character-ized by mixed modes including cyclic cleavage facets,two types of secondary cracks andstriations,etc..The roughness-induced crack closure of fracture surface is attributedprimarily to extreme high fatigue crack growth threshold values.     

铝合金电子束焊接气孔的分析

在电子束焊接试验的基础上,分析了6061-T6铝合金焊缝气孔产生的倾向和坡口表面焊前清理、焊片除气、焊接参数、预热以及重熔方法之间的关系.     

EFFECTS OF MICROSTRVCTURE ON FATIGUE CRACK GROWTH BEHMIOR IN Ni-BASE SUPERALLOY GH586

1.IntroductionInmetalsandalloys,thenearthresholdfatiguecrackgrowthisfrequentlytermed'microstructurallysensitive'.Thisisduebothtotheappearanceofthefracturesllrface,whichisoftenfaceted,andtotilelargevariationsincrackgrowthratewhichcanbeobtainedbyalteringparameterssllchasgrainsize,yieldstrength,ortherelativeproportionsanddistributionsofphasesinthemicrostructure[1].Thisimpliesthatsignificantimprotremelltintotalfatiguelifecouldbeachievedbychangingthemicrostructureofalloys.Therefore,itwouldbeveryadv…     

小幅载荷在A537钢疲劳裂纹扩展过程中作用的研究

采用Ａ５３７钢单边缺口试样，研究了以不同方式叠加在主载荷△Ｐ上的小幅载荷在疲劳裂纹扩展过程中的作用，并采用激光散斑技术测量了循环加载过程中的裂纹闭合效应。结果表明：３０％△Ｐ以下的小幅载荷叠加在主载荷底部时，对由主载荷引起的裂纹扩展速率ｄａ／ｄＮ几乎没有影响，３０％△Ｐ以上的小幅载荷可使裂纹扩展速率增加。叠加在主载荷顶部的各小幅载荷均可使裂纹扩展速率加大。通过对加载条件下裂纹闭合效应的测量，并结合裂尖的应力应变状态的变化进行分析认为：小幅载荷对裂纹扩展速率的影响受裂纹闭合程度的制约，其损伤作用只体现在裂尖材料产生不可逆塑性形变的外加载荷范围内。     

CORROSION FATIGUE CRACK GROWTH OF MEDIUM STRENGTH STEEL HT60 IN SYNTHETIC SEA WATER

The corrosion fatigue crack growth and near-threshold characteristics of a medium strengthsteel HT60 were investigated using compact tension specimens exposed to synthetic sea water.The da/dN-△AK_(eff) relation in air can give a conservative estimation of da/dN-△K relationsin sea water. In the case of high R, however, crack growth acceleration at high △K regionsappears to be cantrolled by the stress-assisted dissolution. The crack opening stressinlensity factor K_(op) detected by the back-face-strain method is the result of crack surface incontact with the corrosion products and therefore an overestimated value of K_(op) at the cracktip is given.     

双相不锈钢中奥氏体相内裂纹扩展路径的透射电镜原位观察

在透射电镜下原位观察了裂纹在双相不锈钢中的扩展过程。结果表明,裂纹在双相不锈钢中奥氏体晶粒内扩展时常呈较大的Z字形扩展路径。并且,在主裂纹前端奥氏体晶粒内形核的小裂纹与主裂纹有较强的交互作用,小裂纹尖端二次滑移系的选择和扩展路径为小裂纹尖端应力场和主裂纹尖端应力场共同支配。     

钢在海水中阴极保护条件下的裂纹扩展特征SCIEI

研究了WFG362钢和A537CL1海洋平台用钢在海水中阴极保护下裂纹扩展的特征。实验结果表明:Ca,Mg沉淀物对裂纹扩展有阻碍作用,使裂纹扩展速率不再随ΔK单调上升,扩展速率曲线成V字型,在一定的ΔK值下扩展速率达到最小值。此外沉积物的作用也使最佳阴极保护电位区间发生了变化,-800—-900mV和-1100—-1500mV为海水中这种材料的最佳保护电位区间,-950—-1000mV范围内为十分有害的区间。     

国产海洋用钢36Z焊缝腐蚀疲劳裂纹扩展的研究SCIEI

本文给出了国产海洋用钢36z焊缝及热影响区在人工合成海水中不同频率的裂纹扩展特征,并与国外同样强度级别的海洋用钢A537焊缝的裂纹扩展率进行了比较。结果表明,在人工合成海水中国产钢焊缝和热影响区低频比高频下的裂纹扩展率分别高3—5倍和4—10倍;国产钢焊缝与A537焊缝的裂纹扩展率基本相当。本文对腐蚀介质下焊缝裂纹扩展规律和断裂特征进行了讨论。     

TRANSFORMATION OF RETAINED AUSTENITE IN CARBURIZED CASE DURING FATIGUE CRACK GROWTH

The morphology of the retained austenite in the carburized case of 20CrNiMo steel and itstransformation during fatigue crack propagation through the case were investigated by usingX-ray and TEM analysis.In the carburized case both film and block shaped retainedaustenite were found.Due to the crystallographic orientation relationship at the interface,thefatigue crack is inclined to pass through the block shaped retained austenite and thereby stim-ulates its strain-induced martensitie transformation.During the process of the fatigue frac-ture,most of the retained austenite structures on the crack path are transformed into themartensite,and the untranaformed parts on the fracture surface remain less than 6%.Thetransformation of the retained austenite,which is restrieted mainly within the plastic zone,oc-curs only during the proeess of fracture,and is independent of the magnitudes of the externalstress,stress ratio and cyclic number.The volume expansion accompanying the transforma-tion creates an additional residual displacement of about 0.44μm on fracture surfaces,whichis equivalent to the magnitude of the plasticity-induced residual displacement.The phasetransformation induced fatigue crack closure is believed to be an important factor affectingthe fatigue crack behaviors in the high carbon laver of the carburized case.     

显微组织对Ti_3Al－Nb系合金疲劳裂纹扩展行为的影响

本文测试了三种显微组织的Ｔｉ３Ａｌ－Ｎｂ系合金的室温疲劳裂纹扩展速率．结果表明，初生α２相的体积分数、基体的晶粒尺寸、高温β转变产物的形貌以及静态屈服强度是影响材料的疲劳门槛值和裂纹扩展速率的重要因素；应力比的影响有着普遍的规律性．结合ＳＥＭ断口及裂纹扩展路径观察结果，对疲劳裂纹扩展行为进行了简单的讨论．