航空发动机用导向叶片叶身裂纹形成机制研究

通过对K441合金导向叶片铸件出现的铸造裂纹及磨削裂纹的观察,并对裂纹处的析出相进行了能谱分析,确定了该导向叶片铸造裂纹和磨削裂纹的形成原因.K441合金导向叶片铸造裂纹的形成与铸件凝固期间补缩能力及合金中C元素含量密切相关.K441合金凝固过程中,除正常枝晶搭接外,在枝晶间析出的碳化物相阻塞了补缩通道,削弱了凝固前沿的界面强度,从而促进热裂纹的产生.合金中碳化物在晶界的析出使叶片磨削裂纹沿晶界形成和长大,并最终导致叶片报废.通过在叶片隔板上增加与冒口相连的补缩通道部分解决了叶片形成疏松和裂纹的问题,而磨削裂纹要通过调整碳化物的析出量和析出形态来解决.     

陶瓷型芯脱除工艺的研究

航空发动机空心叶片的复杂内腔只能用陶瓷型芯来成形,而陶芯的脱除通常用化学腐蚀法。如硅基陶芯在碱液中脱除,氧化镁陶芯在酸液中脱除。但陶芯经高温烧结及浇注合金后,结构较致密,颗粒间结合较牢固。如脱芯工艺选择不当,对复杂薄壁陶芯很难从铸件中脱除;或者因脱芯时间过长,铸件被脱芯液腐蚀,产生过厚的界面层或晶界腐蚀而使铸件报废。因此研究脱芯工艺对生产实践颇有意义。英、美等国对此较为重视,有的成立专门小组进行研究并作了一些报导。国内在脱芯中存在问题很多,尚缺乏研究。     

汽轮机高压导汽管插管P91/P22异种钢焊接接头裂纹原因分析

通过宏观观察、显微硬度分析、显微组织分析等对P91/P22异种钢焊接接头P91钢侧热影响区裂纹进行研究,以分析裂纹的形成机理。结果表明,裂纹位于焊接接头热影响区相变区,并表现为沿晶和穿晶混合型裂纹,裂纹处热影响区硬度值偏高,焊接接头硬度偏高处存在较大残余应力。裂纹产生原因为焊接热处理温度选用不当,造成材料性能出现异常,在残余应力与管道应力共同作用下,出现疲劳裂纹。P91/P22异种钢在使用R407焊条焊接时正确的焊后热处理工温度至少为750℃。     

划伤690TT合金在高温含氧水中应力腐蚀裂纹萌生的研究

利用划伤技术研究了690TT合金在325 ℃高温含氧硼锂水中的裂纹萌生和生长情况。试样表面和截面显微分析的结果表明,划伤沟槽底部局部萌生了典型的沿晶应力腐蚀裂纹。由于应力集中,在慢速率拉伸阶段划伤沟槽底部产生了机械裂纹,而机械裂纹成为恒载过程中690TT合金沿晶应力腐蚀裂纹萌生和生长的先导。尖端非常接近晶界或者沿着晶界的机械裂纹可继续形成沿晶应力腐蚀裂纹。690TT合金在恒载荷条件下对应力腐蚀开裂仍有一定的敏感性。     

DZ4、DZ22定向合金叶片的再结晶分析

对不同寿命的DZ4、DZ22合金叶片进行了解剖分析。结果表明,由于加工工艺的不同,叶片的不同部位再结晶厚度不同,再结晶晶粒沿枝晶轴的生长速率大于沿枝晶间的生长速率。枝晶间的再结晶组织为胞状结构,再结晶组织在叶片的使用过程中没有进一步长大,但存在晶界宽化现象,并有颗粒状碳化物析出。     

定向凝固简化空心叶片热应力数值模拟

定向凝固叶片在凝固过程中产生的热应力会导致叶片最终存在残余应力、变形甚至裂纹而使得叶片报废,故研究叶片凝固过程的热应力变化具有重要意义.通过数值模拟的方法可以对叶片的凝固过程热应力进行模拟,得出应力变化情况,对叶片可能产生的缺陷进行预测.文中采用商用软件ProCAST对定向凝固简化空心叶片的热应力场进行数值模拟,分析空心叶片凝固过程中的热应力变化情况,并通过切割法测量了铸件的残余应力,模拟结果与实验结果吻合较好.     

DZ125高温合金超高周疲劳裂纹萌生与扩展

裂纹的萌生与扩展是研究合金材料超高周疲劳行为的重要方面。本研究分析与探讨了温度和表面状态对DZ125合金的超高周疲劳裂纹萌生与扩展特征的影响。不同温度下,DZ125合金的超高周疲劳裂纹萌生位置和扩展方式不同。室温下,裂纹均沿表面起源,裂纹扩展以拉伸模式为主;700℃下,裂纹均沿亚表面起源,裂纹扩展以剪切模式为主。室温下,DZ125合金经激光冲击处理前后的超高周疲劳裂纹萌生位置和扩展方式均存在差异。经过激光冲击处理后,裂纹萌生于合金的内部孔洞缺陷,裂纹扩展完全以剪切模式进行。     

高温合金单晶铸件中杂晶缺陷的试验研究

分析了高温合金单晶叶片铸件中杂晶缺陷的特征和形成机理。指出杂晶主要产生在铸件横截面大幅度扩张的部位,如缘板和叶冠处,原因是边角处冷却过快,熔体过冷超过了合金的临界形核过冷度。通过试验验证了叶片形状、凝固工艺和合金过冷能力等因素的影响,并提出了这种几何性杂晶形成的条件判据。在生产试验中还发现杂晶也会由其他原因引起,如在型壳内壁的裂纹处和型壳与芯头的间隙中,浇注时渗入的金属液在凝固时形成杂乱晶向的金属披缝,有可能长入铸件形成杂晶。另外,铸件在定向凝固中若产生雀斑缺陷,则雀斑链中的细小等轴晶粒可能会继续生长,扩展为粗大的杂晶组织。条纹晶也可发展成为三维的大尺度杂晶缺陷,但与基体的晶向偏离不会太大。     

熔体处理对某发动机导向叶片铸造裂纹的影响

使用扫描电镜观察了某发动机一级导向器叶片铸造裂纹.发现导致裂纹的主要原因是沿晶界连续分布的碳化物,其弱化了晶界,并阻断了枝晶间的补缩通道,促进了叶片疏松的形成.使用同炉K441母合金在叶片浇注的过程中进行了不同工艺的熔体处理实验.然后使用X射线衍射和扫描电镜分析了叶片相含量和组织的变化,发现合适的熔体处理可以改善碳化物的形态,从而减少铸件的热裂倾向.     

焊接变形与基于SYSWELD的焊接力学数值模拟

汽轮机焊接一直受到由于焊接残余应力和变形所导致的产品成本高、生产效率低等问题的困扰,研究焊接残余应力和变形具有重要的工程实际意义.利用SYSWELD有限元软件完全实现了机械、热传导和金属冶金的耦合焊接计算,既考虑晶相转变又考虑了同一时间晶相转变潜热和晶相组织对温度的影响.分析空心叶片的结构特点和焊接变形原因,利用有限元软件SYSWELD对核电空心叶片的焊接进行了实时三维数值模拟,获得了焊接温度场、焊接残余应力分布及变形,并定性分析了模拟计算结果,为核电空心叶片的七段焊接方法提供理论依据.     

Prospects of the Use of Synergetic Approach to Solution of Problems of the Science of Nanomaterials

A synergetic approach to solution of problems of self-controlled synthesis of nanostructures and creation of self-organizing nanotechnologies is considered in connection with the superproblem of creation of materials with functional properties resembling those of biosystems. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 55 – 61, July, 2005.     

Kinetics of the oxidation of metals — Influence of self-diffusion of metal

The importance of the self-diffusion of a metal during its oxidation by a gas is treated for the cases of nonstoichiometric oxides having either interstitial cation or cation vacancies. We have established a general relationship for the reaction rate when a mixed diffusion process occurs. From this relationship, we have shown that the pressure dependence can be different, according to whether the rate-determining process is the self-diffusion through the metal or through the product.     

胫骨生物陶瓷复合材料的微结构增韧机理

扫描电镜观察显示胫骨是一种由羟基磷灰石和胶原蛋白组成的自然生物陶瓷复合材料.羟基磷灰石具有层状的微结构并且平行于骨的表面排列.观察也显示这些羟基磷灰石层又是由许多羟基磷灰石片所组成,这些羟基磷灰石片具有长而薄的形状,也以平行的方式整齐排列.基于在胫骨中观察到的羟基磷灰石片的微结构特征,通过微结构模型分析及实验,研究了羟基磷灰石片平行排列微结构的最大拔出能.结果表明,羟基磷灰石片长而薄的形状以及平行排列方式增加了其最大拔出能,进而提高了骨的断裂韧性.     

Features of formation of the structure in production of blanks of disks of heat-resistant nickel alloys

Conclusions To provide a high level of mechanical properties in wrought blanks of cast ÉP741NP and ÉP962 alloys it is necessary to form controlled structures. A necklace-type structure formed in homogenizing isostatic treatment, subsequent thermomechanical working including alternation of the operations of deformation in the (+)-area and recrystallization anneals, and final heat treatment is preferable. The temperature conditions of all stages of thermomechanical working are strictly controlled, especially the final operation of deformation and heating for hardening. To eliminate hardening cracks and distortions it is necessary to use molten salts at t=600°C as quenchants. The use of multiple production operations makes it possible to significantly reduce the structural inhomogeneity related to inhertance of the original dendritic structure. However, the structure of the final semifinished product is nevertheless characterized by a difference in occurrence of the processes of polygonization and recrystallization between the former dendritic cells and the interdendritic spaces in deformation and heat treatment.To obtain structurally homogeneous blanks for gas turbine engine parts it is necessary to use basically new methods of remelting such as vacuum double electrode remelting and electron beam remelting with an intermediate vessel.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 25–29, December, 1991.     

Ab-initio calculation of enthalpies of formation of intermetallic compounds and enthalpies of mixing of solid solutions

A large number of ab-initio calculations of energies of formation of intermetallic compounds have been performed in the last 15 years. The currently used methods are listed. The paper presents a review of the aluminium based compounds which have been studied. Comparisons of calculated and experimental enthalpies of formation are provided for aluminim-3d and-4d transition metal alloys at equiatomic composition. The modelling of the enthalpies of mixing of solid solutions based on a given lattice is described.     

试论洋务派教师聘任的思想

洋务派在洋务学堂的办学活动中,为了解决西学专业学科的教学困难,采用了聘请外籍教师的应急措施.他们以真才实学,合同制管理作为主导思想,并认为这种解决师资的途径只是权宜之计,并非久远.从客观上看,洋务派的教师聘任思想有深刻的历史影响.     

Mechanism of Nucleation of Precipitates of Carbides of Refractory Metals Under Hot Rolling of Automotive Sheet Steel

Metal Science and Heat Treatment - The problem of formation of properties in microalloyed sheet steels is considered. The cause and the possible mechanism of precipitation of carbides of refractory...