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以国产蒸汽发生器传热管用GH690合金为研究对象,通过评价其断裂韧性及拉伸特性,结合光学显微镜、扫描电镜和透射电镜分析,研究了合金由室温~623K的力学性能。研究结果表明,室温下GH690合金低的层错能,易生成形变孪晶,使得合金在孪生的协调下塑性变形能力提高,同时孪晶促进裂纹扩展转向,使合金在断裂过程中吸收更多的能量,维持合金高的断裂韧性。随着温度的升高,合金的层错能增加,导致形变孪晶生成困难,合金应力集中程度加剧,裂纹从而平直扩展,合金的断裂韧性降低。由于合金的室温层错能较低,合金在拉伸时能够通过孪生协调变形,同时生成的孪晶阻碍了位错的滑移而提高了合金的强度和塑性。随着形变温度的升高,合金通过孪生协调变形的能力降低,导至合金的变形机制由孪生转变为滑移,滑移产生的加工硬化效应小于孪生,故合金的强度和延伸率随之降低。 相似文献
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Pitting and Stress Corrosion Cracking Susceptibility of Nanostructured Al-Mg Alloys in Natural and Artificial Environments 总被引:2,自引:0,他引:2
Mala M. Sharma Constance W. Ziemian 《Journal of Materials Engineering and Performance》2008,17(6):870-878
The stress corrosion cracking (SCC) behavior of two developmental nanocrystalline 5083 alloys with varied composition and
processing conditions was studied. The results were compared to a commercial aluminum AA 5083 (H111) alloy. The pitting densities,
size and depths, and residual tensile strengths were measured after alternate immersion in artificial seawater and atmospheric
exposure under different loading conditions. Optical and scanning electron microscopy (SEM) with EDX was used to analyze the
fracture surfaces of failed specimen after removal at selected intervals and tensile testing. One of the nanostructured Al-Mg
alloys exhibited significantly superior pitting resistance when compared to conventional microstructured AA 5083. Under conditions
where pitting corrosion showed up as local tunnels toward phase inclusions, transgranular cracking was observed, whereas under
conditions when pitting corrosion evolved along grain boundaries, intergranular cracking inside the pit was observed. Pit
initiation resistance of the nano alloys appears to be better than that of the conventional alloys. However, long-term pit
propagation is a concern and warrants further study. The objective of this investigation was to obtain information regarding
the role that ultra-fine microstructures play in their degradation in marine environments and to provide insight into the
corrosion mechanisms and damage processes of these alloys. 相似文献
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<正> 磷是钢中典型的有害杂质元素,它明显地降低钢的冲击韧性,提高韧性-脆性转变温度,当磷含量达到某一定值时,会造成沿晶脆性断裂。磷对马氏体及其回火组织的冲击韧性和断裂形态的影响已有报道,而磷对珠光体、贝氏体以及马氏体与贝氏体混合组织的韧性和断裂形态的影响研究得较少。本文研究了工程上广泛使用的30CrMnSiA钢淬火非马氏体组织的断裂形态和冲击韧性与磷含量的关系。 相似文献
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A. V. Makarov R. A. Savrai V. M. Schastlivtsev T. I. Tabatchikova I. L. Yakovleva L. Yu. Egorova 《The Physics of Metals and Metallography》2011,111(1):95-109
The structural evolution upon high-cycle fatigue (tension with the magnitude of stress in a cycle below the macroscopic yield
stress) of the hypereutectoid steel U10 (1.03 wt % C), in which pearlite of different morphology (fine-lamellar, coarse-lamellar,
and partially spheroidized pearlite) was formed, has been investigated by scanning and transmission electron microscopy. Based
on the fractographic analysis, features of fracture of these structural states have been considered. At a significant distance
(10 mm) from the fatigue fracture, features of structural transformations caused by cyclic loading have been revealed. It
has been shown that upon high-cycle fatigue in the steel U10 with structures of lamellar and partially spheroidized pearlite,
substantial structural changes occur, namely, fragmentation and partial dissolution of cementite plates, and in fine pearlite,
additionally, spheroidizing of cementite and polygonization of the ferritic component are observed. A dependence of the character
of fracture on the type of structure formed upon fatigue loading has been established. In the steel with a nonequilibrium
structure of unannealed fine pearlite, an enhanced elasticity modulus, as compared to other more stable structures (coarse-lamellar,
annealed fine, and spheroidized pearlite), and a reduction in the magnitude of the elasticity modulus under the action of
cyclic loading have been found. It has been established that the structural changes in fine pearlite of laboratory specimens
of the steel U10 upon cyclic tension are qualitatively similar to those in a railroad wheel of the steel 65G under the service
conditions. 相似文献
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超细晶粒高碳钢微复相组织及性能 总被引:2,自引:0,他引:2
在650℃采用等通道角挤压变形(ECAP)方法对原始组织为层片状珠光体的T8钢进行了Bc方式(每道次挤压后,试样按同一方向旋转90°进行下一道次挤压)的4道次变形,获得了晶粒尺寸在亚微米量级的超微细复相(α+θ)组织,其中等轴铁素体晶粒尺寸约为400 nm,球化完全的渗碳体颗粒粒径约为150 nm。微拉伸实验和SEM断口观察表明,经过4道次ECAP变形后,超微细复相组织的抗拉强度相对于原始珠光体组织而言有所下降,从867 MPa降至819 MPa,但屈服强度显著提高,由479MPa增加到664 MPa,相应的整体伸长率和断面收缩率分别从4.5%、5.2%增加到18%、31%,硬度值变化不明显;超微细复相组织的断口形貌由大量细小的韧窝构成,为典型的韧性断裂,而原始珠光体组织断口形貌则由河流花样组成,呈脆性解理断裂特征。 相似文献
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采用K40钨钴硬质合金搅拌头对3 mm厚热轧退火态亚共析钢板进行了搅拌摩擦加工,对加工区域的宏观形貌、微观组织及力学性能进行了分析.结果表明,搅拌区和热力影响区为先共析块状铁素体、“针状”铁素体及珠光体,组织转变受动态再结晶和相变共同作用,热影响区组织为等轴状铁素体和片层状珠光体.搅拌摩擦加工对各区域中珠光体及析出渗碳体的分布形态影响显著.搅拌摩擦加工后试样显微硬度明显增加,抗拉强度相比母材提高8.2%,断裂位置位于母材处,加工前后试样断裂形式均为微孔聚合韧性断裂.固溶强化与相变强化对硬度和抗拉强度的提高起主要作用. 相似文献
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双相钢空蚀破坏的力学机制 总被引:3,自引:0,他引:3
对由铁素体和渗碳体组成的低、中、高碳钢进行振动空蚀实验,发现它们空蚀破坏的共同特点是铁素体的严重变形和破损.但由于铁素体的含量及分布形态不同,材料空蚀破坏的表现形式大不相同:铁素体含量高的低碳钢以大面积均匀塑性变形为主;铁素体含量与珠光体含量大致相等并呈网状分布的中碳(亚共析)钢是由于铁素体隆起脱落而破坏;以珠光体为主的高碳钢是由于铁素体从渗碳体的夹缝中向外挤出、两相分离而破坏.微射流冲击形成的应力波使低强度相屈服是造成上述破坏的原因. 相似文献
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以大口径(OD1422 mm)、大壁厚(38.5 mm)X80级管线钢热轧板为研究对象,采用光学显微镜和扫描电镜对其显微组织和-20 ℃低温落锤撕裂试验断口形貌进行分析,研究了断裂与组织之间的关系。结果表明,带状组织和不同厚度位置晶粒度大小不均,粒状贝氏体、退化珠光体、准多边形铁素体和马奥岛等混合组织会导致裂纹的萌生和扩展,出现解理断裂,对低温韧性不利,而尺寸为3 μm以下的马奥组织和均匀分布的贝氏体铁素体对裂纹扩展起阻碍作用,说明细小的马奥组织和贝氏体铁素体能够提高钢板的断裂韧性,对低温断裂控制十分有利。 相似文献
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为了探究A286合金的高温持久性能,对采用进口电炉+炉外精炼+真空自耗(EAF+LF+VAR)冶炼工艺制备的A286合金进行不同温度和应力的高温持久试验,利用Larson-Miller参数(LMP)预测了A286合金的持久寿命,并分析了断口微观组织演变。结果表明,A286合金应力与LMP之间的关系为σ=-107.30×LMP+3011.02。随着试验温度的降低,A286合金的断裂方式由韧窝和孔洞组成的韧性断裂转为沿晶断裂的脆性断裂。在低温高应力下,裂纹主要在MC和M23C6处产生,在高温低应力下,裂纹主要在片层状η相处产生。在试验温度650℃、应力450 MPa下,强化机制主要为位错切过γ′相的沉淀强化,在试验温度750℃、应力150 MPa下,强化机制为位错切过γ′相的沉淀强化和位错绕过γ′相的弥散强化,并且晶内析出的TiP2、(Ti, Nb)C、TiC和NbC等纳米颗粒有利于高温持久蠕变。 相似文献
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低碳球墨铸铁断口的观察和分析 总被引:1,自引:0,他引:1
利用扫描电镜(SEM)对珠光体、铁素体和准铸态贝氏体金属基体的低碳球铁拉伸断口形貌进行了分析和研究.结果表明,珠光体低碳球铁的断口应属于脆性断裂的范畴;准铸态贝氏体低碳球铁断口中韧窝明显增多,解理花样大大减少,属于韧-脆性混合型断口;铁素体低碳球铁的断口则完全呈现出韧性断裂的特点.研究还表明,ADI在固态相变时,高温奥氏体快速冷却到贝氏体转变温度的过程中,不可能再形成发达的奥氏体枝晶,也不可能再形成枝晶间的缩松区域.因此,ADI可在获得较高强度的前提下,使材料的韧塑性得到大大提高. 相似文献
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LC4高强铝合金的腐蚀性能研究 总被引:6,自引:0,他引:6
利用慢应变速率拉伸试验方法研究了LC4铝合金在空气和3.5%NaCl溶液中的应力腐蚀断裂行为;利用HB5455-90标准研究了LC4铝合金的剥蚀行为;利用HB5255-83标准研究了LC4铝合金的晶间腐蚀行为。结果表明:LC4铝合金具有应力腐蚀敏感性,应力腐蚀的断口形貌受应变速率ε的影响较大;LC4铝合金对剥蚀很敏感,对晶间腐蚀不是很敏感。 相似文献
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采用GW-1200A型控制器配合高温加热炉在WDW-300电子万能试验机上通过等温压缩实验研究了Ti600合金在温度为25?800℃、应变速率为10-4和10-3 s-1条件下的热变形行为,获得了该合金在变形过程中的真应力-真应变曲线,建立了该合金的高温本构关系。结果表明:Ti600合金在较高的温度(600和800℃)下流变应力随应变速率增大而增大,在较低温度(25和300℃)时变化不太明显。在一定的应变率条件下,随着温度升高流变应力降低。考虑到Ti600合金在不同温度下的真应力-真应变曲线随温度变化的发展趋势,建立了修正的井上胜郎高温本构关系,与实验结果对比验证了模型是可靠的。通过扫描电镜(SEM)观察发现,在室温准静态压缩条件下Ti600合金的断裂形式以脆性断裂为主,同时在局部区域出现韧性断裂特征。 相似文献
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