晶粒形状和碳化物对HK40蠕变裂纹扩展的影响SCIEI

对两种晶粒形状的HK40炉管材料,研究了晶粒形状及碳化物对蠕变裂纹扩展速率的影响。发现当加载方向与柱状晶轴向垂直时,柱状晶材料的蠕变裂纹扩展抗力低于等轴晶材料。二次碳化物对裂纹扩展速率的影响依赖于晶粒形状。     

INFLUENCE OF GRAIN SHAPE AND CARBIDE ON CREEP CRACK GROWTH IN HK40

The influence of two different grain shapes and carbides in the HK40 alloy,the material foruse of furnace tube,on the rate of creep crack growth has been investigated.The resistance tocreep crack growth of the material with columnar grains is inferior than that with equiaxialgrains when the load line is perpendicular to the columnar grain axis.The influence of secon-dary carbide on the rate of creep crack propagation depends upon the Brain shape.     

THE CREEP AND FRACTURE BEHAVIOR OF TWO NICKEL-BASED SUPERALLOYS

1.IntroductionTheevolutionofsuperalloyshasbeengreatlymotiVatedbythedevelopmentofmodernjetengines.Somepartsoftheengineareoperatedathightemperaturesandsubjectedtobothstaticanddynamicforcesaswellasthermalgradients.Therefore,creepcanoccuratsignificantratesandthentheestimationofcreepstrainandtheassociateddamageaccumulationbecomethecriticalconsiderationinthedesignoftheenginebladesoperatingathightemperatures.ThepurposeofthisinvestigationwastoexaminethecreeppropertyandfracturebehaviorofthecastK417and…     

GH864合金蠕变/疲劳裂纹扩展速率及a-N曲线分析

研究了GH864合金不同保载时间下650℃蠕变/疲劳裂纹扩展行为,分析了裂纹扩展过程中蠕变和氧化的作用,以及a-N曲线的转折点含义。结果表明:保载5s时GH864合金以穿晶断裂为主,疲劳作用占主导;保载90s时GH864合金以沿晶断裂为主,蠕变作用占主导。利用Saxena模型可较好地表征本实验条件下650℃蠕变/疲劳交互作用的裂纹扩展速率曲线,可估算较高应力强度因子和较低应力强度因子的裂纹扩展速率。另外,用Saxena模型可求出蠕变和疲劳的表达式,对比分析高温蠕变/疲劳交互作用的裂纹扩展过程中蠕变和疲劳的作用及所占的比例。最后针对a-Ni/Nf、da/dN-a曲线及da/dN-N曲线变换中出现的拐点,结合断口形貌分析了转折点对应的含义。高温合金及其它材料的裂纹扩展速率曲线也适用于以上曲线分析方法。     

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％。     

含铒铝合金显微组织对疲劳裂纹扩展的影响

对含铒铝合金板材进行了不同的热处理,分析了各板材的显微组织对疲劳裂纹扩展和力学性能的影响。结果表明:晶粒的长/径比越小,板材的疲劳裂纹扩展速率越慢;且随着疲劳裂纹扩展速率的降低,裂纹宽度增加且裂纹路径曲折;稀土元素Er的加入,在合金中形成Al_3(Er,Zr)第二相粒子,其强烈地钉扎位错,阻碍位错运动,以减少位错在晶界处的聚集产生的应力集中,降低板材的疲劳裂纹扩展速率。     

Na,K杂质及微量Ce对8090合金裂纹扩展阻力的影响

研究了含0.05%Ce及不同Na,K杂质含量的8090合金薄板裂纹扩展阻力,探讨了合金断裂韧性及裂纹起始扩展阻力随(Na+K)含量变化的规律和微量Ce的作用,结果指出:随(Na+K)含量增加,合金裂纹扩展阻力下降;若(Na+K)含量处于一定范围内时,合金中加入0.05%Ce会改善其断裂韧性及裂纹起始扩展抗力;当(Na+K)含量过高,Ce的这种有益作用便被掩盖,Na,K对合金韧性造成危害的原因之一是可以促使T_1等相沿晶界或亚晶界析出,并促使再结晶晶粒异常长大。     

EFFECT OF Na,K AND Ce ON CRACK PROPAGATION RESISTANCE FOR ALLOY 8090

The crack propagation resistance for alloy 8090 sheet decreases with the increase of content ofNa and K impurities.An improvement over the fracture toughness and crack initiation resist-ance for the alloy containing Na and K within certain limit may be made by adding 0.05%Ce.This beneficial modification would not be manifested if the alloy contained more Na andK.One of the reasons why Na and K injure the toughness of the alloy might be due to thatthey cause the precipitation of T_1 phase along grain and subgrain boundaries and acceleratethe abnormal growth of recystallized grains.     

孔洞式缺陷对γ-TiAl合金断裂行为的影响

采用分子动力学模拟方法研究了孔洞在不同温度、位置以及尺寸下对多晶γ-TiAl合金裂纹扩展的影响。结果表明,含孔洞式缺陷多晶γ-TiAl合金在1～750 K时为脆性解理断裂,1000 K和1200 K为韧性蠕变断裂。孔洞位于晶界和三叉晶界上时,合金更容易失效。与完美晶体相比,微孔洞的存在增加了多晶γ-TiAl合金的塑性。当孔洞半径大于1.0 nm时,多晶γ-TiAl合金的屈服应力和屈服应变急剧降低,材料发生失效的时间提前。孔洞尺寸的不同会影响材料的断裂方式,当孔洞半径R≤0.8 nm时,含孔洞多晶发生沿晶断裂;当R>0.8 nm时,多晶γ-TiAl合金的孔洞不断扩大逐步占满整个晶粒,发生穿晶断裂。     

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.     

晶界碳化物对Fe-Cr15-Ni25合金蠕变裂纹扩展行为的影响SCIEI

在两种不同晶界状态下研究了Fe-Cr15-Ni25合金的蠕变裂纹扩展行为。单相合金的空洞在晶界三叉点处形核,而对晶界上有碳化物析出的合金,空洞在晶界碳化物上形核。晶界碳化物阻碍了空洞的长大和连接,因而大大提高了蠕变裂纹扩展抗力。     

2050铝合金的疲劳裂纹扩展行为研究

研究取样方向、应力比以及微观组织对2050铝合金疲劳裂纹扩展速率的影响。结果表明:取样方向和应力比对疲劳裂纹扩展速率在近门槛区和快速扩展区的影响显著,而在稳态扩展区的影响则相对较小;L-T取样方向的速率最低,T-L取样方向的速率次之,S-L取样方向的速率最高,这主要与合金的晶粒取向、织构取向和第二相粒子取向有关;应力比为0.5的裂纹扩展速率高于应力比为0.1的速率,这在近门槛区主要与裂纹闭合效应有关,在快速扩展区主要受最大应力场强度因子Kmax的影响。     

超声强化2D12铝合金疲劳断裂过程的微观分析

采用超声强化工艺对2D12铝合金进行表面处理,借助金相显微镜和扫描电镜,并结合原位跟踪测量裂纹长度的方法,对强化后的疲劳断裂行为进行了研究。结果表明,超声强化后2D12铝合金表面晶粒得到细化,疲劳源主要产生于试样表面,仅个别向内部转移,强化后疲劳寿命提升了约8倍。其原因一方面是强化过程在试样表面引入了残余压应力,由于裂纹扩展过程倾向于连接裂纹扩展路径上的缺陷,所以残余压应力的存在效降低了裂纹在两缺陷间的扩展速率;另一方面晶粒细化导致晶界密度增加,加强了对裂纹扩展的阻碍,从而有益于提高裂纹扩展寿命。     

Behavior of a submicrocrystalline aluminum alloy 1570 under conditions of cyclic loading

A study of the resistance to fatigue-crack growth in a submicrocrystalline alloy Al-6% Mg-0.3% Sc-0.4% Mn in combination with a precision analysis of the fracture surface of the samples has been performed. A comparison of crack resistance between coarse-grained and submicrocrystalline states of this alloy showed that only at the stage of near-threshold crack growth the velocity of fatigue-crack propagation in the submicrocrystalline state proves to be higher than that in the coarse-grained state. At the stage of linear crack growth, the fatigue-crack propagation becomes insensitive to the grain size. Upon transition to the stage of accelerated crack growth, the velocity of crack propagation in the submicrocrystalline alloy is retarded. A fractographic analysis of the fracture surface of the samples indicates that the retardation of the fatigue-crack growth in the submicrocrystalline alloy is connected with a gradual transition from the intercrystalline to the transcrystalline mechanism of fatigue fracture of the material.     

Einfluß der Mikrostruktur und des Elektroden-potentials auf die Ausbreitungsgeschwindigkeit von Spannungskorrosionsrissen einer reinen AlZnMg3-Legierung in 1 M NaCl-Lösung

Influence of microstructure and electrode potential upon the velocity of stress corrosion cracks of a pure AlZnMg3-alloy in an 1 M NaCI-solution The influence of microstructure and electrode potential upon the stress corrosion crack velocity in a fully aged pure aluminium-zincmagnesium 3-alloy with two step ageing and quench interruption treatments was investigated in airsaturated 1 M sodium chloride solution at 303 K. For this, propagation of the crack tip was observed microphotographically under potentiostatic conditions and under constant load using specimens precracked by fatigue. The crack propagation at the corrosion potential is accelerated by denser matrix-precipitates, narrower precipitate free zone, the presence of great T-grain boundary precipitates and minor sensitivity to intercrystalline corrosion and occurs to judge from the look of the fracture surfaces without considerable metal dissolution. In contrast to the alloy, which shows no intercrystalline corrosion, the crack propagation in the alloy with intercrystalline corrosion is obviously faster above the breakdown potential than at the corrosion potential. The results suggest that the crack propagates essentially mechanically. As mechanisms are discussed a crack growth by anodic dissolution of grain boundary precipitates or of zinc- and magnesium-rich grain boundary regions and mechanical seperation of the intermediate regions and propagation by local hydrogen embrittlement of the crack tip.     

Interkristalline,Kornflächen- und Spannungsriß-Korrosion von ausgehärteten AlZnMg 1-Legierungen

Intercrystalline corrosion, grain-phase corrosion and stress-corrosion cracking of aged AlZnMg1 alloys Potentiostatic polarisation curves and stress corrosion crack propagation of a pure and a commercial AlZnMg1-alloy, both peakhardened either by warm or by double ageing, were investigated in airsaturated sodium halide and sulfate solutions at a temperature of 303 K. For this, propagation of crack tips was observed microphotographically under potentiostatic conditions and under constant stress using specimens precracked by fatique corrosion. The pure alloy contents (weight percent): Zn 4,4; Mg 1,26; Fe 0,05; Si 0,006; balance Al, the commercial alloy: Zn 5,05; Mg 1,2; Fe 0,23; Si 0,1; Mn 0,23; Cr 0,2; Cr 0,2; Ti 0,074; Zr 0,12; Cu 0,056; balance Al. In sodium halide solutions either grain boundary and grain attack or only grain attack occurs at a potential region more positive than the respective breakdown potential. At the more negative restpotential no attack can be observed. The influence of concentration of chloride ions on the velocity of discontinuous crack propagation in the pure alloy, which starts without any initiation stage, is different for both heat treatments. No crack propagation is observed in the commercial alloy and in any case in sulfate solutions. The obtained stress corrosion cracking results may be explained by hydrogen embrittlement of the area around the crack tip.     

锻造工艺对TC4-DT和TC21损伤容限型钛合金疲劳裂纹扩展速率的影响

研究了不同锻造工艺（近β锻造、准β锻造、两相区锻造）对TC4-DT和TC21损伤容限型钛合金疲劳裂纹扩展速率的影响,对比分析了不同锻造工艺的微观组织和疲劳裂纹扩展路径的关系。研究结果表明,与两相区锻造和近β锻造相比,TC4-DT和TC21钛合金经准β锻造后的疲劳裂纹扩展速率最低。准β锻造的锻件疲劳裂纹扩展路径曲折程度大,断口表面粗糙度大,有效地降低了疲劳裂纹扩展速率。     

EFFECT OF CREEP FRACTURE TOUGHNESS ON CRACK INITIATION AND PROPAGATION UNDER CREEP FATIGUE INTERACTION

本文研究了蠕变断裂韧性对三种低合金Cr-Mo-V钢在蠕变一疲劳交互作用下裂纹开裂和扩展的影响.试验表明,材料韧性对裂纹开裂和扩展起重要作用,脆性状态时,裂纹开裂时间比蠕变时短,二者间的裂纹扩展速度无明显差别;韧性状态时,裂纹开裂时间不仅比蠕变时短,而且其裂纹扩展速度比蠕变时大得多.此外,低合金Cr-Mo-V钢经蠕变一疲劳交互作用后有脆化倾向,其脆性程度取决于钢的原始韧性值.韧性状态时,蠕变-疲劳交互作用显著促使三种Cr-Mo-V钢由韧性向脆性转变;而在脆性状态时,这种脆性转变不明显。     

Identification of SAGBO-induced damage zone ahead of crack tip to characterize sustained loading crack growth in alloy 783

Sustained loading was applied to alloy 783 subjected to a non-standard heat treatment, annealing plus γ^′ aging, at elevated temperature. The existence of damage zone ahead of the crack tip was identified and propagation rate of the damage zone was correlated to the sustained loading crack growth rate. The formation of damage zone was ascribed to stress accelerated grain boundary oxidation.