铜基体上爆炸喷涂钨涂层及其电子束热负荷实验研究

详细介绍了爆炸喷涂法在铜基体上制备钨涂层.磁约束核聚变面对等离子体材料要求有承受较高热负荷的性能,电子束辐照热负荷实验发现:0.3 mm的钨涂层可以承受5.13 MW/m2的热通量;在2 MW/m2、20s脉冲的条件下,样品能承受300周的疲劳而没出现破裂现象,且距离表面5 mm处铜基体的温度在70°C左右;5 MW/m2、2 s脉冲的条件下,样品可承受95周热疲劳,且距离表面5 mm处铜基体的温度不高于200°C.钨铜的热膨胀系数和杨氏模量相差很大,在加载热通量过程中,界面处产生应力,这将影响材料的耐热冲击性能,但爆炸喷涂仍然为制备核聚变较低热通量区域面对等离子体材料的一种参考方法.     

钨涂层及氧化镧合金面对等离子体材料研究

介绍了等离子体喷涂钨涂层和粉末冶金钨氧化镧合金面对等离子体材料的制备,并对其进行了性能分析,主要包括微观结构、杂质含量、气孔大小及气孔率分布、结合强度、热导率以及热负荷疲劳性能和承受能力。结果表明:真空等离子体喷涂钨涂层性能比大气喷涂钨涂层性能优越,是更为合适的钨涂层制备技术。真空喷涂钨涂层具有较低的气孔率、较高的热导率、较低的杂质含量和较优异的热负荷性能,能够承受10 MW/m²、100周次疲劳测试。氧化镧弥散掺杂相具有钉扎作用,能够抑制钨烧结过程中的长大,有效提高钨材料强度,改善热负荷性能,W-1%La₂O₃(质量分数)材料能够承受6MW/m²的热负荷。     

SPS烧结W-TaC的耐瞬态热冲击性能

通过高能球磨方法制备了系列W-TaC混合粉末,采用放电等离子体烧结(SPS)制备出弥散强化W-TaC样品,并对W-TaC样品的密度、硬度和微观组织进行了分析。利用60 k W电子束材料测试平台(EMS-60)对烧结W-TaC的耐瞬态热冲击性能进行测试,分别模拟了等离子体破裂和边缘局域模2种热负荷。实验后通过扫描电镜观察了样品加载区域的裂纹及熔化情况,通过透射电镜观察分析了材料的微结构特征。结果表明:W-TaC样品在热负荷作用下可以经受功率密度为740 MW/m~2、5 ms的热冲击而不产生裂纹,但在功率密度为550 MW/m~2、100次1 ms的热疲劳下会产生疲劳微裂纹。SEM和TEM分析表明,TaC颗粒在钨晶粒内和晶粒间都有存在,而且TaC会与W形成共格相界和半共格晶界从而增强钨合金的强度。     

W／Cu功能梯度材料的热应力优化设计

运用有限元软件对W／Cu梯度材料进行了热应力优化设计，结果表明，在30MW／m^2的表面热流负荷下，经过优化设计的W／Cu功能梯度材料有较好的热应力缓和效果，与非梯度材料相比等效热应力降低了62．3％，表面工作温度下降了50℃；与单纯金属W相比，W／Cu梯度材料的表面工作温度较之大幅度降低445℃。     

面向等离子体W／Cu FGM的抗热冲击性能

采用循环水淬和脉冲激光冲击法并结合有限元计算考察和分析了用超高压梯度烧结方法制备的W／Cu FGM的抗热震性能。结果表明，W／Cu FGM经受50次800℃～25℃水淬冲击和100MW／m^2以上的激光循环冲击，没有出现界面破坏现象；但随着热冲击次数及冲击能量密度的增加，金属W表面产生了裂纹、晶间断裂以及出现液相及蒸发现象。与非梯度材料相比，W／Cu FGM有优异的抗热冲击性能，大致可以经受100MW／m^2 350次以上的激光循环冲击。     

1Cr18Ni9Ti/20G双金属爆炸焊接界面裂纹的扩展行为

利用奥氏体不锈钢／低碳锅炉钢（1Cr18Ni9Ti/20G）爆炸焊接复合板，通过电子束焊接得到带有界面裂纹的三点弯曲J积分裂纹扩展阻力试样和四点弯曲疲劳试样。分别进行了带界面裂纹材料和相应单一材料试样的裂纹扩展阻力曲线及其疲劳扩展行为的实验研究。结果表明：双材料界面裂纹的静态和动态扩展阻力均低于裂纹在相应单一材料中的扩展阻力。     

Thermal Performance and Microstructure of Vacuum Plasma Sprayed Tungsten Coatings under Cyclic Heat Load

采用真空等离子喷涂技术在铜基体表面制备了钨涂层,分别通过NiCrAl和W75Cu25涂层作为中间层。5 MW/m2, 2 s的高热负荷电子束实验表明NiCrAl中间层提高了涂层的热导率并降低了热应力和残余应力值。W75Cu25涂层作为中间层则表现出较差的热疲劳性能。高热负荷电子束真空等离子喷涂钨涂层表现出侵蚀和微裂纹。因热应力导致涂层发生塑性变形,在高温情况下裂纹起源于熔融的钨颗粒,但是,裂纹被钨涂层塑性变形和孔洞所抑制     

面向等离子体高热负荷部件中的关键性连接技术

介绍一种C/C复合材料与铜合金热沉的大面积连接技术,C/C表面首先经过激光毛化处理,再经活性浇铸一薄铜层,后通过钎焊或电子束焊与CuCrZr合金实现大面积连接.数值模拟结果显示,这种连接可以稳态承受10 MW/m2的热负荷长期作用;电子束模拟热负荷试验结果也显示,平护瓦型碳纤维增强复合材料连接结构在经受12 MW/m2热负荷,1 000次热疲劳试验后没有出现热烧伤斑点等损伤现象;Monoblock型连接结构在经受15 MW/m2,300次热疲劳试验后,也没有出现明显的损伤现象.结果表明,该种连接技术完全可以满足EAST装置高热负荷部件5～8 MW/m2的需要.     

真空等离子喷涂钨涂层组织与热行为研究（英文）

采用真空等离子喷涂技术在铜基体表面制备了钨涂层,分别通过NiCrAl和W75Cu25涂层作为中间层。5 MW/m2,2 s的高热负荷电子束实验表明NiCrAl中间层提高了涂层的热导率并降低了热应力和残余应力值。W75Cu25涂层作为中间层则表现出较差的热疲劳性能。高热负荷电子束真空等离子喷涂钨涂层表现出侵蚀和微裂纹。因热应力导致涂层发生塑性变形,在高温情况下裂纹起源于熔融的钨颗粒,但是,裂纹被钨涂层塑性变形和孔洞所抑制。     

适配层对钨铜第一壁材料热负荷性能的影响

介绍了W/Cu PFC(Plasma Facing Components)材料制备过程,并对不同适配层第一壁材料热负荷性能进行了研究。其结果显示,虽然W-Cu混合材料、Ti和NiCrAl适配层的应用均抬高了第一壁材料的表面温度,但是承受10MW/m2热负荷时无任何损伤,而无适配层的材料在7.5MW/m2时表面出现微裂纹损伤,由此判断适配层的应用能够增强W/CuPFC的热负荷性能。     

High heat flux tests on brazed divertor components in electron and ion beam test facilities

Two different designs of single-tube metallic heat sinks with carbon armour tiles, designed by the Next European Torus (NET) team and manufactured by Metallwerk Plansee, were tested under thermal loading conditions simulating the normal operation parameters expected for the NET/ITER (International Thermonuclear Experimental Reactor) divertor. The experiments were performed in the Material Research Ion Beam Facility (MARION) and the Jülich Divertor Test Facility/Hot Cells (JUDITH), both at the Research Centre Jülich, and in the JAERI Electron Beam Irradiation Stand (JEBIS) at the Japan Atomic Energy Research Institute. The thermal response of the components was determined by stepwise increase of the heat flux, and the thermal fatigue behaviour was studied by cyclic loading at different heat flux levels. Additionall, finite elements analysis of the temperature and stress fields resulting from thermal loading was performed.

No failure of the brazes resulted from exposing the component to a peak heat flux of 20·7 MW/m² in the screening test. In the thermal fatigue experiments, 300 cycles at 15 MW/m² were sustained in JEBIS, whereas in MARION, failure occurred after 376 cycles at 10 MW/m² surface heat flux. The results of the numerical analysis showed good agreement with the values measured in the experiments.     

Effect of various heat and surface treatment conditions on the fatigue behavior of SKD11 steel

Effects of various heat treatment processes, including Q/L-T, Q/H-T, Q/L-T + Ti-nitriding, Q/H-T + Ti-nitriding, and Q/CT/H-T on the S-N fatigue behavior of SKD11 steel were investigated. Ti-nitriding is a modified nitriding process that entails a small addition of approximately 2 g to 20 g of electrolyzed fine, metallic titanium in a salt bath. In the present work, depending on the applied stress and surface conditions, different crack initiators were operative, resulting in three types of crack initiation. Multi-site crack initiation around the specimen surface, observed only for the Ti-nitrided specimens at a high stress range, decreased the resistance to S-N fatigue by reducing the crack initiation cycles, Ni. At low and intermediate stress ranges, the cracked carbide particles located near the surface or internally served as crack initiators for all the specimens, regardless of whether Ti-nitriding was applied, resulting in similar resistances to S-N fatigue. Different heat treatment parameters, such as tempering temperature and cryogenic treatment, did not affect the fatigue behavior of SKD11 steel to any considerable degree. The fatigue behavior of SKD11 specimens with different heat and surface treatment conditions is discussed based on micrographic and fractographic observations.     

Ti-6Al-4V合金的超高周疲劳行为

采用超声疲劳实验分别确定了双态和网篮两种组织的Ti-6Al-4V合金的疲劳寿命(S-N)曲线,并用SEM观察疲劳断口.结果表明,两种组织合金的S-N曲线均保持下降趋势,在105-109cyc间不出现水平段,不存在传统意义的疲劳极限,断口形貌分析表明,随着应力幅的降低,二者的裂纹萌生位置都发生了由试样表面到内部的转变.与加载频率为25 Hz时的疲劳实验结果进行比较后发现,超声疲劳加载条件下,疲劳强度提高,疲劳寿命延长,且频率对网篮组织合金疲劳性能的影响大于对双态组织的影响.     

DZ125定向凝固高温合金的超声疲劳行为研究

利用超声疲劳试验方法研究DZ125合金在105～109循环周次范围内的疲劳性能,其载荷频率为20kHz.结果表明:DZ125合金疲劳断裂寿命在105～108循环周次范围内;扫描电镜观察表明,DZ125合金的超声疲劳裂纹均起源于表面,疲劳断口的起源区由多个斜面组成,存在明显的滑移台阶形貌特征,从合金的超声疲劳裂纹扩展形态...     

Gigacycle fatigue properties for high-strength low-alloy steel at 100 Hz, 600 Hz,and 20 kHz

Fatigue tests were carried out at frequencies of 100 Hz, 600 Hz, and 20 kHz for low-temperature-tempered JIS SNCM439 steel. Almost all specimens were broken from internal inclusions and frequency effects were not found on the gigacycle fatigue properties. The fatigue limit appeared at over 10⁹ cycles.     

Fatigue-life prediction of SiC aluminum composite using a Weibull model

The feasibility of the acoustic emission technique in predicting the residual fatigue life of 6061-T6 aluminum matrix composite reinforced with 15 vol.% SiC particulates (SiC_p) is presented. Fatigue damages corresponding to 40, 60 and 80% of total fatigue life were induced at a cyclic stress amplitude. The specimens with and without fatigue damage were subjected to tensile tests. The acoustic emission activities were monitored during tensile tests. The number of cumulative AE events increased exponentially with the increase in strain during tensile tests. This exponential increase occurred when the material was in the plastic regime and was attributed mainly to SiC particulate/matrix interface decohesion. Cumulative events during post fatigue tensile tests reduced with a decrease in the residual fatigue life. Based on the high cycle fatigue damage accumulation model, a Weibull probability distribution model is developed to explain the post fatigue AE activity of specimens during tensile tests. Using the model, the residual fatigue life can be predicted by testing the specimen in tension and monitoring the AE events. In high cycle fatigue, it was observed that the residual tensile strengths of the material did not change significantly with prior cyclic loading damages since the high cycle fatigue life was dominated by the crack initiation phase.     

Effect of stress ratio on long life fatigue behavior of Ti-Al alloy under flexural loading

A new ultrasonic three-point bending fatigue test device was introduced to investigate fatigue life ranging up to 10^10 cycles and associated fr＇dcture behavior of Ti-Al alloy. Tests were performed at a frequency of 20 kHz with stress ratio R=0.5 and R=0.7 at ambient temperature in air. Three groups of specimens with different surface roughness were applied to investigate the effect of surface roughness on fatigue life. Furthermore, optical microscopy（OM） and scanning electron microscopy（SEM） were used for microstructure characteristic and fracture surface analysis. The S-N curves obtained show that fatigue failure occurs in the range of 10^5-10^10 cycles, and the asymptote of S-N curve inclines slightly in very high cycle regime, but is not horizontal for R=0.5. Fatigue limit appears after 10s cycles for R=0.7. Surface roughness （the maximum roughness is no more than 3 μm） has no influence on the fatigue properties in the high cycle regime. A detailed investigation on fatigue fracture surface shows that the Ti-Al alloy studied here is a binary alloy in the microstructure composed of α2-Ti3Al and γ-Ti-Al with fully lamellar microstructure. Fractography shows that fatigue failures are mostly initiated on the surface of specimens, also, in very high cycle regime, subsurface fatigue crack initiation can be found. Interlamellar fatigue crack initiation is predominant in the Ti-Al alloy with fully lamellar structure. Fatigue crack growth is mainly in transgranular mode.     

Thermal fatigue mechanism of recrystallized tungsten under cyclic heat loads via electron beam facility

Thermal fatigue resistance of plasma facing materials (PFMs) is an inevitable concern for component lifetime and plasma operations, since the temperature fluctuations will always exist in future nuclear fusion facilities and reactors. Accordingly, experiments were performed in the electron beam facility to investigate the thermal fatigue behavior under operational loading conditions. The tungsten is investigated in its stress relieved and fully recrystallized state for a better understanding of the thermal fatigue process when exposed to cyclic heat loads. The heat loads range from 24 to 48 MW/m² and the number of cycles increases from 100 to 1000 times. The results indicate that the thermal fatigue damage (surface roughening) due to plastic deformation strongly depends on the loading conditions and the cycle index. As the power density and the number of cycles increase, the density of the intragranular shear bands in each grain becomes higher and the swelling of grain boundaries becomes more pronounced. The shear bands are generally parallel to different directions for varying grains, showing strong grain orientation dependence. Additionally, extruded flake structures on shear bands were observed in these damaged areas. It found that the shear bands are generally parallel to the traces of {112} slip planes with the surface. The results suggest that slip plastic deformation represent the predominant mechanism for thermal fatigue and a set of schematic diagram is presented to explain the formation of thermal fatigue damage morphology (extrusion and intrusion structures).