Al双晶体的晶界疲劳效应SCIEI

通过Al双晶体疲劳试验,研究了晶界对循环变形和疲劳裂纹扩展的影响。实验结果表明,晶界疲劳效应集中体现于晶界影响区,表现为不相容塑性应变在该区内产生内应力,并由此可激发次级滑移,甚至产生晶界裂纹;在常幅循环应力下,随超Ⅰ阶段裂纹逐渐接近晶界,裂纹分叉、前沿碎裂,扩展速率降低,直至在晶界影响区中央达到一最小值。本文提出了晶界诱发裂纹顶端屏蔽机制,并以此解释了上述超Ⅰ阶段裂纹对微观组织敏感的扩展行为。     

CYCLIC DEFORMATION OF COARSE GRAINED POLYCRYSTALLINE PURE Ai——Ⅰ.SLIP CHARACTERISTICS

Comparing with ordinary ploycrystalline materials sized to μm grade,the slip morphology ofthe coarse grained polycrystalline pure Al is characterized by:(1)several slip domains occurin a grain,and in same domain,several slip systems operate at same time or one after anotherintensely,a beautiful and neat slip pattern is forming on the specimen surface;(2)for highΣ-value coincident and random grain boundaries,the grain boundary affecting zone(GBAZ),bout 50—120μm wide,is favourable site to form intergranular crack at early fa-tigue life easily,and migration or slide of the boundaries were often observed.While lowΣ-value near-coincident grain boundaries show a higher degree of slip continuity and straincompatibility than high Σ-value ones.Intergranular crack is not easily nucleated at lowΣ-value near-coincident boundaries;and(3)due to suppression of grain boundary slip attriple grain boundary node,the high Σ-value and random grain boundary among the threeboundaries of tricrystal crack easily during cyclic deformation.     

疲劳裂纹尖端的位错结构

在双相钢物理短裂纹门槛区，观察到稳定的位错胞和墙结构；长裂纹门槛区，在铁素体／马氏体相界堆垛位错密度大，有形成位错胞的趋势．长裂纹扩展第二阶段，铁素体晶粒内具有单向滑移线（Ｒ＝０，－１）和正交网状（Ｒ＝－１）的位错结构，长裂纹扩展第三阶段，位错稀少，但单滑移、双交滑移位错线明显拉长，说明裂纹尖端位错组态是应变历史的产物．疲劳裂纹扩展门槛区形成的位错胞和墙是一亚稳态结构，与门槛循环应力应变处于动态平衡，也是一微观结构参数．     

IN SITU OBSERVATION OF FATIGUE CRACK GROWTH IN CENTRIFUGAL SPRAY DEPOSITION (CSD) Ti 48Al 2Mn 2Nb ALLOY

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A crystallographic mechanism for fatigue crack propagation through grain boundaries

A crystallographic model is proposed which takes into account both crack-plane twist and tilt effects on crack retardation at grain boundaries. The twist and tilt angles of the crack-plane deflection at a grain boundary are the key factors that control the path and growth rate of a short crack. Because of crack-plane twist, the area between the traces on the grain-boundary plane of the crack planes across the boundary has to be fractured in order for the crack to propagate through the boundary. This presents significant resistance to crack growth. As the area to be fractured increases with the extent of crack growth beneath the surface of observation, the grain boundary could still resist crack growth after the crack tip has passed the grain boundary on the surface, until the crack propagates through the whole boundary below the surface. A grain boundary with a large twist component could cause a short crack to arrest or branch. Studies of short fatigue crack growth in an Al–Li 8090 alloy plate provide evidence that supports the model.     

EBSD Analysis of Fatigue Crack Growth of 2124 Aluminum Alloy for Aviation

运用电子背散射衍射(EBSD)分析技术对2124-T851铝合金板材的疲劳裂纹扩展进行了分析研究。结果表明,疲劳裂纹扩展以穿晶为主,随晶粒取向的不同而呈现一定的择优性。当裂纹扩展到晶界时,由于相邻晶粒间存在的取向差,裂纹会偏离其正常扩展路径而发生偏转,而晶内的裂纹偏转则更多是因为粗大第二相粒子在循环应力作用下协调变形能力差引起的。裂纹扩展过程中发生裂纹分叉与特定的晶体学方向有关,是由于裂纹尖端多个等效{111}<110>滑移系的同时开动造成的。     

循环载荷下裂尖形变规律的实验研究

应用散斑干涉技术，在常幅载荷下对疲劳裂纹扩展过程中的一个循环周期内，不同加载阶段的裂尖应变、裂纹张开位移进行了原位测量，给出了裂纹闭合对裂纹张开位移及裂尖形变的影响规律。结果表明：由于裂纹闭合和残余压应力的存在，疲劳裂尖应变与外加载荷的平方并不成正比，在加载初期，裂纹处于闭合状态，裂尖应变无明显变化，随着载荷的增加，裂纹逐渐由远离裂尖处张开并向裂尖发展，一旦裂纹完全张开，裂尖应变迅速增加，对裂尖应力-应变状态的分析表明，裂尖材料的应力-应变关系类似于光滑试样低周拉压疲劳应力-应变滞后关系。     

CRACK GROWTH BEHAVIOR AND FRACTURE FEATURE OF GH2132 UNDER CREEP-FATIGUE CONDITIONS

1.IntroductionSuperalloysareirreplaceableinengines[llandenginesundergostaticandcyclicloading[2].Thereforeitisimportanttostudycrackgrowthbehaviorofsuperalloysundercreepfatigueconditions.Itisnoticedthattheeffectofcyclicloadingoncrackgrowthisconsiderablel3'4],butdifferentatalowstresslevelfromthatatahighoneIS'6].Itisfoundthattheyieldstrengthofmaterialsisanimportantparameterinstudyingfatiguepropertiesl7,8]andcrackgrowthic,lo].Soitisofmuchimportancetocorrelatecrackgrowthbehaviorandfracturefeaturew…     

铜双晶体中晶界及组元晶体的疲劳寿命

本文对具有单,双滑移取向组元晶体的近生趣晶界铜双晶体进行拉－拉循环变形,得出铜双晶体中晶界及组元晶体的Ｓ－Ｎ曲线,比较了铜双晶体晶界及组元晶体疲劳寿命的差别,发现在相同的应力幅下晶界的疲劳寿命明显低于组元晶体的疲劳寿命。     

7050铝合金晶界偏析与应力腐蚀,腐蚀疲劳行为的研究

研究了不同时效状态的７０５０铝合金晶界偏析与应力腐蚀开裂及湿空气环境下疲劳裂纹扩展的关系，并采用修正的化学方法计算了晶界偏析对断裂应力的影响。结果表明：随着时效程度的增加，晶界上Ｍｇ偏析浓度减小，捕获Ｈ的能力减弱，晶界断裂应力的百分数随之下降，因而合金的抗应力腐蚀和腐蚀疲劳性能提高。     

EFFECT OF ZIGZAG GRAIN BOUNDARY ON CREEP RUPTURE OF A 10Cr-15Co-Ni-BASE WROUGHT SUPERALLOY

应用两种热处理制度分别获得弯曲晶界和平直晶界,研究两种晶界状态对10Cr-15Co-Ni基变形高温合金蠕变断裂过程的影响,重点探讨弯曲晶界改善合金热强性原因。研究表明,弯曲晶界对裂纹的萌生、长大及扩展,对裂纹的形态及断裂方式,都有显著的影响。弯曲晶界能有力地阻止晶界滑动及推迟裂纹连接,使晶内参与更多的变形,弯晶的主要作用体现在蠕变第三阶段。合金经弯晶处理后蠕变断裂寿命提高26％。     

PPB对镍基粉末高温合金裂纹扩展速率的影响

摘 要: 研究了直接热等静压（As-HIP）成形的一种镍基粉末高温合金中原始颗粒边界（PPB）对其裂纹扩展行为的影响。结果表明,粉末高温合金中的原始颗粒边界上析出的碳、氧化物会导致断裂韧性(KIC值)降低,使界面极易萌生裂纹;在裂纹扩展过程中发生沿颗粒间断开,改变扩展棱的走向,并加剧裂纹沿晶界扩展,使裂纹扩展速率增快;沿原始颗粒边界扩展的裂纹尖端的断裂韧度与边界析出物的物理性质、数量、尺寸密切相关,析出物排列越密集,KIC值越小,会加速裂纹在这些薄弱区扩展。     

HIGH TEMPERATURE CRACK PROPAGATION AND FRACTUREOF SUPERALLOYS

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EFFECT OF GRAIN BOUNDARY CARBIDE ON CREEP CRACK GROWTH IN Fe-Cr15-Ni25 ALLOY

Creep crack growth behavior of Fe-Cr15-Ni25 alloys with different grain boundary featureshas been studied.Cavities nucleate at triple junctions of grain boundaries for the single phasealloy and at grain boundary carbide for the alloy with grain boundary carbide.Grain bounda-ry carbide particles are obstacles to cavity growth and coalescence,and therefore increase thecreep crack growth resistance greatly.     

CRACK GROWTH, FRACTURE FEATURE AND RUPTURE LIFEDURING CYCLIC CREEP OF SUPERALLOY GH2132

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光滑试样在低频交变载荷下早期应力腐蚀裂纹扩展的阻滞

在低碳钢/(1NNa_2CO_3+1NNaHCO_3溶液)系统中,曾经观察到光滑试样的应力腐蚀裂纹在低频交变载荷作用下出现早期扩展阻滞现象,本工作采用70/30黄铜光滑试样在1NNaNO_2水溶液中的应力腐蚀开裂对这一现象进行了研究分析。实验结果说明:该阻滞效应在细晶粒黄铜中比在粗晶粒黄铜中更为显著;前者在晶界或孪晶界形成的裂绞数目比后者的要多得多;采用预裂绞试样能够消除这一阻滞效应。用光滑试样表面多重裂绞萌生可对以上结果作出解释一多重萌生的裂纹在早期扩展阶段有效地分散了裂绞尖端的应变集中。     

Fatigue crack retardation by silicon carbide powder paste infiltration under different cyclic stress conditions*

Fatigue crack retardation with infiltrated SiC paste into a crack is examined in low carbon structural steel. Two different sizes of SiC powders, whose average diameters are 15 and 53 μm, are used. The SiC powder mixed with oil is infiltrated into a through thickness fatigue crack from the crack mouth. Fatigue crack growth retardation is examined by the ΔK increasing test of R = 0.1, comparing with the base plate property, where ΔK is stress intensity factor range and R is stress ratio. Crack growth is retarded just after infiltrating SiC paste into the crack mouth, and the deceleration of crack growth rate to 1/50 of the base plate appears in the maximum. It is revealed that this crack retardation behaviour results from the crack closure induced by the wedge effect of the SiC particle into a crack. The crack retardation effect is investigated with several combinations of SiC particle size and cyclic stress conditions. The crack growth rate, da/dn and stress intensity factor, K_cl for the crack closure depend on both the maximum stress intensity factor, K_max, and the stress ratio, R. While the better retardation effect can appear in the higher K_max and the higher R ratio, it disappears in the R ratio over 0.7. The SiC paste with 15 μm powder brings the crack retardation effect in the wider cyclic stress condition more stable than in the SiC paste with 53 μm powder.     

HQ-80钢再热裂纹机理

通过插销、冲击韧度等试验研究HQ-80钢的再热裂纹倾向，扫描电镜发现过热区晶界存在合金元素碳化物，电子能谱检测碳化物富含Cr、Mo。再热裂纹的机理是，高温过热——合金元素碳化物固溶，再热弱化——晶界析出大颗粒状合金元素碳化物导致晶粒表面的贫Cr、Mo合金元素层．晶界高温强度不足。影响再热裂纹三要素是：生成品界碳化物的Cr、Mo、C等合金元素，高温过热与再热弱化的热循环过程，一定的拘束应力。再热裂纹与再热脆化的机理相同，两者同时发生，降低应力防止再热裂纹并不能防止再热脆化。成功采用无缺口插销进行插销试验，弧形断口证明再热裂纹的主要影响因素是过热区敏化组织。     

Cu双晶的循环形变行为与疲劳裂纹萌生：Ⅱ.疲劳裂纹萌生与早期扩展

用扫描电镜观察了受应变疲劳载荷作用的Ｃｕ双晶物的表面形貌，发现晶界是疲劳形变双晶是有利的裂纺萌生地点，在滑移带撞击晶界的地方，特别是在几条粗滑移带共同撞击晶界的地方观察到许多疲劳微裂纹；并且发现与平行晶界双晶相比，垂直晶界双晶有有利于疲劳裂纹沿晶界作早期扩展。