微波烧结ZrO_(2(n))/Al_2O_3复合陶瓷工艺与组织

以纳米ZrO2、微米Al2O3为原料,采用微波烧结方式制备ZrO2/Al2O3复相陶瓷。探讨了烧结温度和保温时间对试样线收缩率、相对体积密度、硬度和断裂韧性的影响。结果表明,烧结温度1550℃,保温时间10 min,可得到较高的硬度(13 350 MPa)和较好的断裂韧度(6.41 MPa.m1/2),烧结过程中发生了m-ZrO2转变为t-ZrO2相变,nano-ZrO2的加入使Al2O3形成內晶型结构;试样的断裂方式为沿晶断裂和穿晶断裂并存;ZrO/AlO复合陶瓷主要通过应力诱导相变和内晶型结构进行增韧。     

3Cr13不锈钢弹片断裂分析

3Cr13马氏体不锈钢所制弹片在工作306 min后返厂复试,复试试验中发生断裂.利用微距照相机和扫描电镜对失效弹片断口和侧面、失效弹片人工断口、未失效弹片的人工断口进行宏观和微观观察,并用能谱仪对个别区域进行成分分析,利用显微硬度计对两种弹片进行了硬度检测.结果表明:弹片受到应力腐蚀作用,萌生沿晶裂纹,之后发生疲劳扩...     

Ti17合金网篮组织的断裂韧性及其预测模型研究

研究了Ti17钛合金网篮组织的断裂韧性及断裂行为,发现裂纹扩展路径曲折度(外因)及沿着裂纹扩展路径所消耗的塑性功(内因)对断裂韧性有显著影响,好的塑性及曲折的裂纹扩展路径有利于提高合金的断裂韧性。基于能量原理,建立了综合考虑内因和外因的断裂韧性预测模型,模型预测精度较高,误差在6%以内。分析模型发现,对网篮组织断裂韧性起决定作用的是其本征塑性功,占80%以上,裂纹扩展路径的贡献较小,在20%以内。     

Influence of Cr element on impact fracture process of ductile Ni-resistant alloyed iron at low temperature

In this study, in order to investigate the influence of Cr element on the impact fracture process of ductile Ni-resistant alloyed iron at low temperature, different contents of Cr element were added to ductile Ni-resistant(DNR) austenitic alloyed iron. The experimental results show that Cr addition can increase the hardness of the DNR alloyed iron, but it has an destructive effect on low-temperature impact properties. Through the analysis of the dynamic load and absorbed energy of samples with different Cr contents in the impact fracture process, and the comparison of the impact fracture process at room and low temperatures, it reveals that Cr addition into the DNR alloyed iron can facilitate the formation of the carbide mixture in Mn23C6 and Cr23C6 with homogeneous and discontinuous distribution. Meanwhile, Cr addition also can improve the the maximum dynamic load and crack initiation energy at low temperature, but has no obvious effect on the yield behavior of the DNR alloyed iron in the impact fracture process. Compared with the impact crack propagation process at room temperature, the metastable propagation energy at low temperature declines significantly with an increase in Cr content. This is because the micro-cracks that caused by the carbides weaken the matrix, resulting in the decline of impact crack propagation resistance. The fracture analysis results also show that the impact fracture mechanism gradually transforms from ductile to brittle with an increase in Cr content at low temperature. It explains that too much Cr addition can lead to brittle fracture even though the austenitic matrix has a good toughness at low temperature.     

Fatigue crack propagation behavior of K40S cobalt-base superalloy at elevated temperature

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脱硫系统塔底重沸器壳体应力腐蚀开裂分析

采用化学成分、金相组织、断口形貌及腐蚀产物的能谱分析等方法分析了脱硫系统塔底重沸器产生裂纹的原因.结果表明,重沸器断口较平整,母材、焊缝的化学成分和金相组织正常,断口表面呈现沿晶开裂现象,部分区域还存在树枝状二次裂纹,开裂的原因是由于长期在富含H2S环境中及焊缝附近有较高的焊接残余应力,并提出了相应的防护和改进的措施.     

新型转子钢25Cr2Ni4MoV的焊接性及接头性能

根据新型转子25Cr2Ni4MoV成分和合金特点,分别进行HAZ硬度、斜Y坡口裂纹、冷裂纹插销试验等,由试验结果可知,该钢种的冷裂纹敏感性强,焊接时预热温度应大于300℃。对接头常温力学性能和高温短时拉伸测试,结果表明该钢焊后的接头强度接近母材,塑性较好,焊缝的冲击韧性较高,接头微观组织为回火贝氏体和少量铁素体组织,断口由脆性断裂区和纤维断裂区组成,脆性断裂区为沿晶和准解理,随着预热温度的提高,沿晶成分减少,准解理部分增多。     

热浸铝钢等离子体电解氧化陶瓷层的微观力学特性

采用纳米压入方法表征了热浸镀铝钢表面由Al2O3层、Al层和FeAl层组成的复合涂层的纳米硬度、弹性模量及断裂韧性等微观力学性能,采用扫描电镜(SEM)观察了纳米压痕形貌,并分析了孔洞对陶瓷层的纳米压入行为和压痕裂纹扩展的影响.结果表明:等离子体电解氧化(PEO)陶瓷层中包含许多微米和亚微米尺度的细小孔洞,陶瓷层弹性模量约为226.4 Gpa,纳米硬度约为19.6 Gpa.当纳米压入深度为250 nm时,所测得陶瓷层的力学参数分散性较大.与FeAl层比较,PEO陶瓷层具有较高的裂纹扩展阻力. FeAl层纳米压痕顶端产生了沿直线扩展的径向裂纹;而陶瓷层纳米压痕中除径向裂纹外出现了侧边裂纹.     

45Mn2螺栓非正常拉伸断裂原因分析

某厂生产的45Mn2螺栓进行拉伸实验时出现非正常断裂,采用宏观断口分析、金相分析等方法对断裂螺栓进行了分析.结果表明,非正常断口的形成是螺栓在拉伸前螺纹根部就存在裂纹.螺栓根部长的裂纹是淬火中形成的,在冷挤压螺栓时螺纹根部就形成微裂纹,这些微裂纹淬火时成为根部淬火裂纹形成的关键原因.     

AZ91系列压铸镁合金高周疲劳断口形貌分析

AZ91D压铸镁合金中加入富Ce稀土后,组织得到明显细化,压铸过程中产生的气孔变小,分布更加均匀,能够减少疲劳裂纹源的产生。AZ91D合金拉伸断口表现为既有解理台阶又存在细小撕裂棱及韧窝的混合断裂特征,加入1?后,合金断口的韧性断裂特征增加,有利于提高合金的室温力学性能。AZ91D合金疲劳裂纹源萌生于合金内部的气孔和夹杂处,疲劳裂纹沿晶界扩展,加入稀土后,疲劳裂纹扩展区有疲劳辉纹出现,疲劳断裂呈现出准解理和韧窝断裂的混合特征。     

Room—temperature mechanical properties of WSi2／MoSi2 composites

Five Kinds of WSi2/MoSi2 composites were successfully prepared by mechanical alloying,IP and high temperature sintering techniques.And their hardness and fracture toughness were measured by the Vickers indentation fracture mode through an Hv-10A type sclerometer.The microstructure and morphology were investigated by a JSM-5600IV scanning electron microscope.Results show that the addition of 50% WSi2(in mole fraction)has remarkable hardening and toughening effects on the MoSi2 matrix.whose hardness value and fracture toughness value are increased about 60% and 86%,respectively.For WSi2/MoSi2 comosite,the hardening mechanisms are fine-grain and the second phase particles strengthening,and the toughening mechanisms include fine-grain,grain drawing,crack deflection,microbridge and bowing toughening.     

铸造γ+α双相不锈钢的裂纹生长与扩展速率

采用阶梯能量示波冲击试验法研究了铸造双相不锈钢冲击弯曲破断时,裂纹的萌芽、生长、扩展3个阶段与载荷-位移曲线及断口的对应关系,研究了裂纹的生长与扩展速率。结果表明,裂纹萌芽于屈服后的第2个载荷-位移曲线高峰。裂纹生长的临界尺寸对应于载荷-位移曲线平台后的第2个下跌槛。裂纹生长对应于断口上的启裂区。裂纹扩展对应于断口上的扩展区。在启裂前区裂纹以较低速率波动生长,启裂后区裂纹的生长速率更趋减缓。裂纹扩展的前期扩展速率很高,后期则迅速下降。裂纹从萌芽到生长至临界尺寸耗费了总破断功的76.2%。     

工业铸造A357铝合金SEM原位拉伸实验

通过场发射扫描电镜装载原位拉伸台,对不同凝固条件下工业铸造A357铝合金进行原位拉伸试验。结果表明,裂纹微裂纹首先萌生于组织中破裂的共晶硅处,近邻的微裂纹连接形成小裂纹;多处形成的小裂纹彼此连接并形成较长裂纹,沿共晶区深化和扩展,逐渐发展为主裂纹;当主裂纹遇到铝基体时,扩展受阻,裂纹发生钝化并在其前沿区域形成剪切带;剪切带深化并开裂,主裂纹沿着深化的剪切带穿过基体继续扩展,最终导致试样断裂。A357铝合金的断裂方式为兼具韧性断裂和解理断裂的混合断裂。反重力铸造有效地改善合金微观组织形态,提高了合金的力学性能。     

TA15钛合金锻件裂纹分析

TA15钛合金锻件在加工过程中,发现加工表面存在裂纹。通过对裂纹形态、裂纹断口的宏微观特征、裂纹金相、材质组织及硬度等检测与分析,得出了裂纹性质及产生原因,并通过裂纹断口温色对比分析以及断口微区成分分析,获得了裂纹产生的温度范围。结果表明,TA15钛合金裂纹为锻造折叠裂纹,折叠裂纹在锻造过程中发生了扩展。裂纹主要是由于表面没有清理干净的氧化皮卷入所致。裂纹左侧棕红色断口形成温度高于800℃,右侧灰色断口形成温度不高于500℃。     

微观组织对TA15 ELI钛合金损伤容限性能的影响

研究了TA15 ELI钛合金43 mm厚板的等轴组织、双态组织和片层组织的室温拉伸性能、断裂韧性(KIC)以及疲劳裂纹扩展速率(da/dN)等损伤容限性能,通过金相显微镜观测了疲劳裂纹在各类组织中的扩展规律,讨论显微组织对该合金损伤容限性能的影响.结果表明该合金等轴组织和双态组织的室温力学性能和疲劳裂纹扩展阻抗差别不大;相对等轴组织和双态组织而言,该合金片层组织在损失强度较小的前提下(Rm=992 MPa),合金断裂韧性提高,达到111 MPa·m1/2,同时该合金的疲劳裂纹扩展速率也大幅降低,其Paris公式拟合参数为c=1.08×10-8,n=3.23,具有更好的损伤容限性能.     

裂纹深度和强度组配对焊接接头断裂性能的影响

利用弹塑性有限元计算和三点弯曲试验对不同裂纹深度，不同强度组配焊接接头试样的断裂性能进行了研究，着重讨论了裂纹深度和组配的不同对焊接接头试样加载过程中塑性区形状及大小，深浅裂纹分界点，抗断性能，裂纹尖端张开位移ＣＴＯＤ，Ｊ积分的影响。结果表明，裂纹越浅。加载时塑性区域大，断裂韧性值越高，高组配焊接接头试样加载时由于塑性区扩展到母材而具有较大的塑性区，低组配焊接接头试样加载时塑性区被抑制在焊缝中，尺     

大型精轧支撑辊疲劳断裂失效分析

某单位1580生产线精轧支撑辊在轧制过程中突然发生断裂,为查明失效原因,利用光学显微镜、拉伸、冲击试验机以及扫描电镜对轧辊材料显微组织、力学性能、断口形貌、起裂源位置进行了综合分析。结果表明,精轧支撑辊芯部材料为球墨铸铁,其组织主要由珠光体、棒状渗碳体、球状石墨及聚集在石墨周围的牛眼状铁素体构成。组织洁净度较差,夹杂物主要为球状Al₂O₃-MgO-SiO₂、Al₂O₃-MgO、Al₂O₃氧化物,尺寸集中在10～15 μm。支撑辊断口呈现典型旋转弯曲疲劳断口特征,裂纹源区位于轧辊内部且为多源起裂,断口内部呈现典型“鱼眼”特征,“鱼眼”区中最大夹杂物直径3 mm,为球状Al₂O₃-MgO-SiO₂。裂纹源最大拉应力30 MPa。裂纹在夹杂物周围萌生时其裂纹尖端最大应力强度因子为1.385 MPa·m^1/2,大于内部起裂裂纹扩展门槛值,因此裂纹在夹杂物与基体界面处形核。裂纹扩展至“鱼眼”区之外时,裂纹在应力作用下快速扩展并汇聚形成一条长裂纹,最终导致轧辊发生瞬断。     

B101连续油管应力腐蚀开裂行为分析

研究了连续油管的抗H2S环境应力腐蚀开裂(SSCC)行为.利用扫描电镜(SEM)观察了断口形貌,用能谱仪(EDS)分析了断口元素组成,从环境因素、材料组织、化学成分等方面分析了断裂机理.结果表明,母材对应力腐蚀不敏感,焊缝是应力腐蚀的薄弱区域.焊缝断裂可分为裂纹孕育期、裂纹发展期、裂纹快速增长期、完全破坏期.应力在72...     

Effect of Trace Element on Microstructure and Fracture Toughness of Weld Metal

The microstructure and fracture toughness of weld metal under Ti-free and Ti-containing different fluxes were investigated in this study.It was found that the trace element Ti of flux in submerged arc welding produced significant influence on the fracture toughness.The addition of 60 ppm Ti induced the sharp increase in J_(0.2) value from 232.78 to 364.08 kJ/m~2.Microstructure characterization revealed that a large number of oxide inclusions prompted the nucleation of acicular ferrites and refined grains,which improved the fracture toughness of Ti-containing weld metal greatly.Moreover,the crack propagation path was more tortuous and bifurcated due to the small amount of carbide precipitations along grain boundaries and blocky martensite-austenite islands for Ti-containing weld metal.Meanwhile,the large-angle grain boundaries caused crack deflection and increased the resistance of crack propagation compared to Ti-free weld metal.     

起落架40CrNi2Si2MoVA钢螺桩断裂分析

起落架40CrNi2Si2MoVA钢螺桩在安装一段时间后发生了断裂。为确定螺桩断裂的原因,对断裂螺桩断口宏微观形貌、断裂螺桩及对比件的氢含量、材料的性能以及表面损伤等因素进行了检查,并对电镀工艺进行了评定。结果表明,裂纹主要起源于第一螺纹根部的机械损伤部位,源区以沿晶断裂特征为主,断裂件含氢量较高。综合分析认为。螺桩断裂性质为氢致延迟断裂,表面机械损伤对氢吸收和扩散的促进作用和40CrNi2Si2MoVA钢材料高强度所致的高氢脆敏感性是导致断裂的主要原因。