高热负荷作用下钨的热疲劳损伤研究

利用实验室自主搭建的电子束热疲劳测试系统,研究了再结晶态钨在功率为141.5 MW/m~2,不同循环次数下热疲劳损伤性能的变化规律。采用扫描电子显微镜(SEM)观测了损伤后表面形貌的变化,采用原子力显微镜(AFM)观测了损伤表面的三维形貌的变化,同时也测出损伤表面粗糙度。采用显微硬度计测试了热疲劳损伤后晶粒表面显微硬度的变化。结果表明:随循环次数的增加,钨热疲劳损伤加剧,当循环1000次时,钨表面已经有熔融的形貌出现;测得损伤表面的粗糙度随循环次数呈近似线性变化;损伤之后的显微硬度先升高后降低,主要是由于存在疲劳硬化的现象。     

核聚变堆用钨及钨基材料热负荷损伤行为的研究进展

聚变堆在运行过程中面对等离子体钨基材料需要承受住一定次数稳态和瞬态热负荷的冲击而不发生开裂以及熔化等损伤。对商业钨在不同测试手段下热负荷的损伤行为进行了分析,阐述超细晶粒钨、合金化、掺杂碳化物以及稀土氧化物等改性手段对钨基材料热负荷性能的影响;对面对等离子体钨基材料热负荷损伤行为进行了总结与展望。     

氮等离子体预辐照对钨中氘滞留的影响

利用直线等离子体模拟装置开展氮和氘等离子体注入钨的实验,采用微分干涉差显微镜(DIC)、场发射扫描电子显微镜(SEM)结合聚焦离子束(FIB)以及X射线光电子能谱仪,分别研究氮和氘等离子体辐照前后钨表面成分、形貌和微观组织结构的变化,采用超高真空热脱附系统对氮等离子体预先辐照后钨中氘的捕获状态和滞留总量进行分析。结果表明:经氮辐照后,钨样品表面形成了氮化钨相,进一步注入氘等离子体后其表面起泡增多,氘在钨中的滞留总量升高。这是由于氮化钨相的形成阻碍了氘原子沿表面方向扩散逃逸,使氘原子在钨的亚表面过饱和聚集,导致钨中氘致起泡现象更加明显。     

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。     

强流脉冲离子束作用下超细晶钨的抗瞬态热负荷性能评价(英文)

采用高能球磨和放电等离子体烧结技术制备纯钨、氧化物弥散强化钨和碳化物弥散强化钨。为了评价钨在瞬态热冲击下的性能,采用强流脉冲离子束,在热流密度高达160MW/(m2·s-1/2)的条件下对4种不同晶粒尺寸的钨进行抗热冲击试验。与商品钨相比,弥散强化钨在瞬态高热流作用下显现出不同的行为。氧化物弥散强化钨显现出较差的抗热冲击性能,这主要是由于低熔点的第二相Ti和Y2O3的引入,从而使得钨的表面发生熔融、起泡和开裂。而碳化物弥散强化钨合金则显现出较好的抗热冲击性能。     

等离子喷涂纳米氧化锆涂层的热震失效机理研究

采用合理的喷涂工艺参数制备了纳米氧化锆涂层并在1100度下测试了其热震性能,利用XRD,SEM和TEM对涂层的结构及表面形貌进行了分析。实验结果显示孔隙或早期存在的微裂纹附近的纳米颗粒在热震实验过程中会长大。通过对结构分析,我们提出了在循环应力作用下纳米涂层的失效机理。即随着纳米结构涂层中的大多数或者全部的纳米颗粒长大后,纳米结构随之变为准微米结构,其热震失效模式将类似于传统微米涂层的失效方式—裂纹形成,扩展直至最后涂层剥落。     

基于疲劳热耗散试验的金属温度场分析方法

本文以300M钢的疲劳试验为基础,借助非接触式红外热像仪,观察了疲劳测试过程中温度场的变化,以热力学第一定律和热交换定律为基础,综合了G.Meneghetti的单位体积金属热耗散模型;从微观角度分析了不同热处理条件下300M钢微观晶粒度对疲劳损伤过程中温度变化的影响,从宏观角度考虑了载荷和循环周次与疲劳过程中试件温度变化的关系,通过多元函数逼近建立了以晶粒度、载荷水平、循环周次为自变量的当量热源模型描述热源。该模型可以通过插值的方法来快速定量确定金属表面的温度场和当量热源大小。最后,数值模拟该热源的效能,通过实验验证,发现该模型可以有效预测疲劳损伤过程中温度场的演化。     

WC-Co硬质合金热机械腐蚀疲劳性能的研究

采用自行设计的实验装置对两种WC-Co硬质合金在压压循环载荷和循环加热冷却同时作用下的热机械腐蚀疲劳行为进行了研究,研究了冷却介质pH值和Co含量对硬质合金热机械腐蚀疲劳性能的影响,同时采用SEM对断口形貌进行了分析.实验结果表明:疲劳断裂的宏观形貌主要是切断型的断裂,疲劳裂纹稳定扩展区上存在很多摩擦碎屑,在稳定扩展区并没有发现疲劳条纹的存在,瞬断区的断裂形貌与静态断裂特征一致.在本文所提供的热机械腐蚀疲劳实验条件下,并未发现冷却介质pH值对两种WC-Co系列的硬质合金的热机械腐蚀疲劳性能的影响,低Co含量的硬质合金YGH30具有比高Co含量硬质合金YGH60更优异的热机械腐蚀疲劳性能.     

喷雾造粒预合金化W-Ni-Fe三元合金粉末及射频热等离子体致密球化研究

球形致密化的钨基（W-Ni-Fe）合金粉末对增材制造等粉末成形构件的强度等物理性能的提升具有重要意义。采用喷雾造粒和射频热等离子体高温致密球化处理的方式研究了W-Ni-Fe粉末经喷雾造粒后射频热等离子体处理对其合金粉末的形貌、孔隙等的作用效果。研究表明,经喷雾造粒后所形成的96W-2.5Ni-1.5Fe三元合金粉末显微组织结构疏松,内部中空洞较多且表面粗糙;射频热等离子体对喷雾造粒粉进行处理后其综合性能提高,球形粉表面孔洞及疏松现象有所缓解,但仍有部分颗粒表面与内部存在微孔,且致密球化后的W晶粒之间Ni、Fe相含有较高含量的W元素。     

机械球磨时间对W-Nb合金氦辐照行为的影响

实验采用不同球磨时间制备W-Nb复合粉末,并通过放电等离子烧结方法制备W-Nb复合材料。所得的W-Nb复合材料用剂量为9.90×10₂₄ ions/m₂的氦离子束辐照11分钟,随后分别在900、1100和1300℃下热处理1小时。实验结果表明,球磨时间不同导致复合材料中钨铌固溶程度不同,进而造成了材料抗辐照损伤性能的差异。其中,球磨36小时的试样的固溶程度最低,其在辐照后表面损伤也最严重,表面出现了纳米绒毛状结构。此外,在同一个样品中,钨的不同的晶面取向也导致了不同的表面损伤形貌。通过对比不同热处理温度的试样,发现富铌区域的晶粒发生了明显的长大,但富钨区域的表面形貌几乎没有变化。这是由于铌的加入使得He在钨中的解吸峰右移。     

CuW合金的细观累计损伤及裂纹演变模拟分析

考虑到细观累计损伤与微观结构的相互关系,对CuW合金的二维代表体单元施加循环载荷,应用Darveaux模型分析了CuW合金的累计损伤以及所引起的裂纹演变。分析结果表明：塑性滑移带首先形成于CuW合金的铜相区,随着循环次数的增加,细观损伤及裂纹萌生于钨颗粒的棱角处并沿着其边缘扩展,微裂纹的扩展路径主要受钨颗粒的分布状况影响,而烧结颈在一定程度上迟滞了微裂纹的扩展速度。     

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).     

圆筒内嵌钨合金球爆炸加载条件下断裂机制研究

针对钨合金作为预制破片战斗部穿甲后的易碎性,采用圆筒内嵌钨合金球战斗部,研究了97.5W-Ni-Fe合金在圆筒内嵌式爆炸加载穿靶前后的微观组织以及断裂机制。结果表明,97.5W-Ni-Fe合金爆炸加载后在钨颗粒内部产生大量形变孪晶,穿透靶板后形变孪晶诱发大量微观裂纹,微裂纹在穿靶后的拉应力作用下扩展并与W-W界面断裂相互连接,使钨合金球断裂成有效破片,增强了钨合金的二次毁伤能力。     

Characteristics of tungsten coatings deposited by molten salt electro-deposition and thermal fatigue properties of electrodeposited tungsten coatings

Tungsten coatings were obtained on a tungsten substrate by molten salt electrodeposition (MSE) at 50 mA/cm² for 60 min in a NaCl-KCl-NaF-WO₃ (0.3385:0.3385:0.25:0.0 73mol) melt at 800 °C. The MSE tungsten coatings have rough rectangular pyramid surface and special columnar grains structure. Thermal fatigue tests have shown that the damage factor of MSE tungsten coatings was smaller than that of rolled tungsten under the same thermal loads and MSE tungsten coatings displayed better thermal fatigue properties compared to that of rolled tungsten, which was attributed to high purity, special columnar grains and rectangular pyramid surface morphology.     

基于弥散强化钨基面向等离子体材料研究进展

重点综述了国内外关于氧化物或碳化物作为强化相的钨基面向等离子体材料的力学性能、氢滞留特性以及辐照损伤,发现制备工艺和强化相含量是影响钨基面向等离子体材料力学性能的主要方面,而均匀分散的强化相颗粒所致使的组织致密化程度更高是钨基材料力学性能提高的主要因素。其次,阐述了晶界和晶内的强化相颗粒分散不均表现出的位移损伤、气泡、绒毛、微裂纹等缺陷都将增加材料对氢同位素的捕获几率,以及等离子体辐照造成的脆化硬化将降低材料的抗热冲击性能。最后分析了近些年弥散强化钨基面向等离子体材料存在的关键基础问题,展望了未来弥散强化钨基材料的主要发展趋势,期望为开发优异的抗高热负荷和辐照损伤的钨基材料方面提供重要参考。     

Size effects in the fatigue behavior of thin Ag films

Thin film dimensions and microstructure affect the microscopic processes responsible for fatigue. This work focuses on the characterization of such mechanisms and the resulting fatigue behavior. The fatigue behavior of 0.2–1.5 μm thick, Ag films on SiO₂ was investigated. The films were tested using cantilever microbeam deflection with respect to the influence of loading conditions. Extrusions similar to those observed in bulk material were found at the Ag film surfaces after cyclic loading. Voids observed beneath the extrusions, close to the film-substrate interface, contributed significantly to fatigue failure. Fatigue damage was observed to occur predominantly in (100)-oriented grains. Thinner films were more fatigue resistant and contained fewer, smaller extrusions than thicker films.     

Microstructural evolution of W-10Re alloys due to thermal cycling at high temperatures and its impact on surface degradation

This paper features four microstructurally different tungsten 10 wt% rhenium (W10Re) alloys tested by thermal cycling at high temperatures in a conventional electron beam welding machine. The sample surfaces undergo minimum temperatures of 1700–1750 °C with 3.000–180.000 additional temperature jumps of 170–200 °C. The used materials show microstructural changes as well as surface damage related to the exposure time and the number of applied temperature jumps. The loaded surfaces show formation of slip bands, grain boundary bulging, pitting, thermal grooving as well as crack formation after the cyclic thermal loading.An initial columnar grain structure reduced pitting of grains at the surface by influencing the preferential crack direction, while on the other hand increasing surface swelling. Introducing HfC into the W10Re matrix led to a smaller final grain size after recrystallization as well as decreasing surface swelling and pitting. A larger initial grain size has shown increased surface degradation and large amounts of swelling. The changes in microstructure were characterized by classical metallographic means including light optical microscopy and hardness testing. The surface damage was investigated in detail by using laser scanning microscopy. Differences in surface damage mechanisms were characterized by electron back scatter diffraction and scanning electron images. The combination of temperature measurements with finite element modeling enabled to calculate the temperatures and loading conditions of the samples.     

Classification of corrosion defects in NiAl bronze through image analysis

Corrosion surface damage in the form of pitting and micro-cracks is observed in many metals. Cracks usually initiate from the pits and grow under cyclic stresses and eventually lead to material failure. An image analysis based on wavelet transforms and fractals was used to study the corrosion morphology of nickel aluminum bronze metal under varying corrosion conditions and applied stresses. Image feature parameters were extracted and analyzed to classify the pits/cracks in the metal samples. The results obtained indicate that classification of pits/cracks is possible with image analysis and may be used for correlating service/failure conditions based on corrosion morphology.     

钨涂层面对等离子体材料损伤演变行为研究

利用等离子体喷涂技术制备了钨涂层面对等离子体材料,并对涂层基本性能进行了表征,主要包括气孔率,相对密度,结合强度,热导率,硬度分布,进而研究主动水冷钨涂层在热负荷服役条件下损伤演变行为。研究发现,直接水冷钨涂层内部层与层之间的开裂、分层是涂层失效的原因,损伤演变过程为柱状晶体再结晶并长大、层间微裂纹出现、裂纹扩展和气孔出现、最后材料分层、失效。间接水冷钨材料的热负荷性能受到很大限制,且疲劳性能降低,失效形式是涂层开裂或脱落,甚至铜基体整体熔化。     

Dislocation structures in the bands of localised cyclic plastic strain in austenitic 316L and austenitic-ferritic duplex stainless steels

Dislocation structures in bands corresponding to cyclic strain localisation have been studied in two types of stainless steels, single phase austenitic 316L steel and two-phase austenitic-ferritic duplex steel. Dislocation structures are documented in thin foils oriented approximately perpendicular to the active slip plane of individual grains and parallel to the primary Burgers vector. Persistent slip bands, with the structure more or less reminiscent of the well-known ladder structure, were found in austenitic grains of both steels. These bands can be correlated with the distinct surface relief consisting of extrusions, intrusions and shallow surface cracks in austenitic phase. No clear features which can prove the existence of the persistent Lu¨ders bands in austenitic grains were found. The distribution of the wall and labyrinth structure embedded in the matrix structure in ferritic grains, which was proposed to be responsible for the localisation of the cyclic strain, however, does not correspond to the distribution of the distinct surface slip lines on the surface.