带缺口的熔模铸造TiAl合金断裂特性的扫描电镜原位观察(英文)

采用感应凝壳熔炼技术和熔模铸造方法制备TiAl合金。在增量加载情况下,采用扫描电镜原位观察技术观察带缺口的熔模铸造TiAl合金试样的裂纹扩展和断裂特性。在拉伸变形的整个过程中,观察并分析裂纹萌生、扩展直至断裂的全过程。结果表明,TiAl合金的断裂机制不仅对于缺口区域附近的微裂纹敏感,而且与层片方向和加载轴的位向有关。当局部应力大于TiAl合金的断裂韧性时,高的拉伸应力就会导致裂纹萌生、扩展直至断裂失效。因此,TiAl合金的塑性和高的拉伸应力导致带缺口的TiAl合金的断裂失效。     

加载速度对TiAl基合金缺口弯曲断裂机制的影响

主要就加载速度对TiAl基合金2种组织缺口弯曲断裂机制的影响进行了详细研究.研究结果表明:在缺口弯曲试验中,裂纹沿着局限于缺口根部中心线上的高应力区起裂并扩展;全层组织断裂韧性随加载速度的变快而增加,而双态组织断裂韧性随加载速率的增大几乎没有变化,这主要是由于在不同加载速度下全层组织在加载速度快和慢时的断裂过程不同,双态组织则是相同的;全层组织试样具有较差的拉伸性能,但是具有较高的断裂韧性,这是由于2种试验时的断裂机制不同.在拉伸试验时大层团晶粒引起严重的损伤和低的强度;然而在3PB试验中大层团形成更大的分叉裂纹以及形成穿过主裂纹扩展的更大阻碍物.     

缺口对铸造单一取向层片组织TiAl合金断裂行为的影响

研究了缺口对铸造单一取向层片组织TiAl合金断裂形貌特征和断裂机制的影响。通过对断口进行观察发现,缺口对单一取向的层片组织有较大影响。研究表明,在光滑试样的拉伸过程中,裂纹起源于试样内部,然后迅速扩展至断裂;在缺口试样的拉伸过程中,微裂纹于断口边缘产生,在切应力的作用下扩展、连接形成裂纹稳态扩展区,然后在正应变控制下从裂纹稳态扩展区向裂纹失稳扩展区过渡,同时试样失稳。     

750℃热暴露对定向层片组织铸造TiAl合金室温拉伸塑性的影响

研究了大气中750℃,48~300 h热暴露对定向层片组织铸造TiAl合金室温拉伸塑性的影响,并采用拉伸中途卸载、染色渗透后再次加载直至断裂的方法,分析因表面脆性层诱发的微裂纹的形成和扩展行为,以揭示定向层片组织在热暴露后保持更好室温拉伸塑性的原因.结果表明,定向层片组织TiAl合金在750℃热暴露150 h后室温塑性仍大于2.0%,300 h热暴露后尚保持1.0%的水平,其热暴露致脆程度远小于双态组织和其它层片组织.在430 MPa应力下,微裂纹起源于脆性贫Al层,并在后续加载过程中扩展进入基体.此裂纹起到尖锐缺口的作用,约束了材料的塑性变形,导致TiAl合金室温拉伸塑性降低.对于定向层片组织,由于层片界面平行于基体表面,有利于抑制微裂纹在后续加载过程中向基体扩展,从而使合金在热暴露后保持较高的室温塑性.     

近全层组织γ-TiAl基合金的室温拉伸断裂机理

通过对直缺口近全层组织的扫描电镜原位拉伸实验以及相应的断裂表面观察，结合有限元计算了TiAl基合金近全层组织拉伸的断裂机理。研究表明：许多裂纹在塑性变形前沿着层间起裂和扩展，断裂过程的驱动力是拉应力。在直缺口试样中，许多裂纹直接起裂于缺口根部，并且沿着层间扩展。随着拉应力的增加，主裂纹和新裂纹也可以通过障碍晶粒的穿层解理断裂来连接。通过有限元计算得沿层断裂强度大约为50MPa，穿层断裂强度大约为120MPa。     

Ti555211合金双态组织拉伸行为的SEM原位观察

利用SEM原位拉伸实验,研究了Ti555211合金具有初始双态组织的拉伸变形和断裂行为。结果表明:在拉伸载荷作用下,双态组织试样中滑移带优先出现在初生α相内(与拉伸轴呈45°),在裂纹扩展过程中,合金内滑移带的密度均随着载荷的增加逐渐增加,双态组织试样的断裂方式为微孔聚集型断裂。原位拉伸试样断口分析表明,韧性断裂是双态组织试样的主要断裂方式,双态组织试样断口没有明显剪切唇,存在小范围的剪切滑移造成的平坦面。SEM原位拉伸实验分析方法能够对该合金的变形和断裂行为进行实时跟踪,该方法的研究结果更加具有重大的理论价值和工程意义。     

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 本文通过拉伸试验研究了铸造TiAl合金单一取向层片组织在缺口应力集中系数分别为2、3和4时的缺口敏感性。发现,该合金在沿层片界面方向的应力作用下,对应各Kt水平的缺口试样均具有大于光滑试样的抗拉强度,且其缺口敏感系数相当;并根据该合金具有较好的拉伸塑性和缺口拉伸断口上存在裂纹萌生和稳态扩展区域的特征,分析讨论了其形成缺口强化效应的机制。     

双态组织TiAl基合金拉伸塑性的断裂力学

探讨了双态组织TiAl基合金中晶粒尺度对合金常温拉伸塑性的影响. 对等温锻造后的γ-TiAl基合金进行了热处理, 获得了含有不同等轴γ晶粒及片层晶粒体积比的双态组织. 采用单轴拉伸实验, 对断口进行分析发现 双态组织的断裂方式是脆性断裂, 在片层区域以穿晶解理断裂为主, 而在以等轴γ区域为主的细晶区以沿晶断裂为主. 通过统计断裂力学分析, 建立了双态组织TiAl基合金拉伸塑性模型, 并得出结论 只有在晶粒半径细化到50μm以下, 才会对拉伸塑性产生较大的影响.     

单一取向层片组织TiAl合金缺口敏感性的研究

通过拉伸试验研究了铸造TiAl合金单一取向层片组织在缺口应力集中系数分别为2、3和4时的缺口敏感性。发现该合金在沿层片界面方向的应力作用下,对应各Kt水平的缺口试样均具有大于光滑试样的抗拉强度,且其缺口敏感系数相当;并根据该合金具有较好的拉伸塑性和缺口拉伸断口上存在裂纹萌生和稳态扩展区域的特征,分析讨论了其形成缺口强化效应的机制。     

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。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

The Mirror with Patterns of Auspicious Animals and Grapes——Exquisite cast mirror and the technology of surface tin-enrichment by rubbing-in and infiltration of tin-rich powder

<正>Bronze mirrors were used by the Chinese people before the introduction of the glass mirror.Only after it was replaced by the glass mirror did the bronze mirror gradually retreat from people's lives.Different styles of bronze mirrors were made in different historical periods,particularly in the Warring States Period,the Han and Tang Dynasties,which were the three peaks of the development of bronze mirror arts in ancient China.The casting techniques were exquisite.The surface of the bronze mirror was smooth and bright enough to reflect one's image,and there were scarcely any casting defects on the mirror surface.On the back of the bronze mirror,there were rich depictions of Arts and Humanities,and the ornamentations were also     

The 9th China International Diecasting Congress & Exhibition

The 9th China International Diecasting Congress ＆ Exhibition was held on July 22-24, 2014 at Shanghai New International Expc Centre. This exhibition was the most successful over the years, with over 6890 visitors and 155 exhibitors, and the exhibition area increased by 30% from 9,500 square meters in 2012 to 12340 square meters. Die casting enterprises from a total of 24 countries and regions, including China mainland, Chinese Taiwan and Hong Kong, South Korea, Japan, Germany, India, Thailand, Malaysia, the United States, Russia, Australia, Iran, Ukraine, Brazil, Colombia, Singapore, Austria, Canada, Croatia, France, Turkey, United Kingdom, Vietnam, attended the congress and exhibition.     

Introduction of the Fluid Control Engineering Institute of Kunming University of Science and Technology

正The Fluid Control Engineering Institute of Kunming University of Science and Technology was set up in 1996.The researches of institute concentrate on electro-hydraulic(pneumatic)servo/proportional control and hydromechatronics.The Institute is committed to research and development of electro-hydraulic control of high-end technical equipment in ferrous metallurgy refining produc-     

RARE METALS Volume Contents

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Antimony Induced Crystallization of Amorphous Silicon

Antimony induced crystallization of PVD (physics vapor deposition) amorphous silicon can be observed on sapphire substrates. Very large crystalline regions up to several tens of micrometers can be formed. The Si diffraction patterns of the area of crystallization can be observed with TEM (transmission electron microscopy). Only a few and much smaller crystals of the order of 1μm were formed when the antimony layer was deposited by MBE (molecular beam epitaxy) compared with a layer formed by thermal evaporation. The use of high vacuum is essential in order to observe any Sb induced crystallization at all. In addition it is necessary to take measures to limit the evaporation of the antimony.     

A CUMULATIVE FATIGUE DAMAGE RULE UNDER THE ALTERNATIVE OF CORROSION OR CYCLIC LOADING

Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic loading was proposed. The specimens of aluminum alloy LY12-CZ soaked in corrosive liquid for different times were tested under the constant amplitude cyclic loading to obtain S-N curves. The test was carried out to verify the proposed cumulative fatigue damage rule under the different combinations among corrosion time, loading level, and the cycle numbers. It was shown that the predicted residual fatigue lives showed a good agreement with the experimental results and the proposed rule was simple and can be easily adopted.