共查询到20条相似文献,搜索用时 0 毫秒
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Wei GUO Yaping ZONG Gang WANG Liang ZUO Department of Materials Science Engineeing Northeastern University Shenyang China 《材料科学技术学报》2004,20(3):245-248
The effects of applied tensile strain on the coherent α2→O-phase transformation in Ti-Al-Nb alloys are explored by computer simulation using a phase-field method. The focus is on the influence of the applied strain direction on the microstructure and volume fraction of the O-phase precipitates. It is found that altering applied strain direction can modify microstructure of Ti-25Al-10~12Nb (at. Pct) alloy during α2→O-phase transformation effectively and full laminate microstructure in the Ti-25Al-10Nb (at. Pct) alloy can be realized by an applied strain only along the direction 30° away from the α2 phase <1010> in magnitude equivalent to the stress-free transformation strain. The simulation also shows that not only the magnitude of applied strain but also the applied strain direction influences the O-phase volume fraction and the effect of strain direction on the volume fraction is up to 25%. 相似文献
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Two types of Fe–32 at.%Ni bicrystals containing a 90°{211} tilt or a 90°<211= twist grain boundary were prepared to investigate the effect of grain boundary character on the martensitic transformation behaviour. The martensite-start temperature (Ms) of bicrystals with the tilt boundary was significantly higher than that of single crystals, while Ms of bicrystals with the twist boundary showed no significant difference from that of single crystals. Near the tilt boundary, the coarse lenticular martensites were symmetrically formed in the neighbouring grains. In contrast, the tiny martensites were homogeneously distributed in bicrystals with the twist boundary, similar to those in single crystals. In the vicinity of the tilt and the twist boundaries, some variants with the habit plane almost parallel to the boundaries were preferentially selected among 24 variants; moreover, the equivalent variants in neighbouring grains were adjoined at the tilt boundary. As a result, the compatibility of shape strains across the boundary was maintained in the case of the tilt boundary, resulting in increasing the Ms. Such characteristic nucleation of martensites can be regarded as an example of self-accommodation across the boundary, which is called cooperative nucleation (C–N). From a crystallographic viewpoint, C–N can occur only at the symmetric tilt boundary. Effects of pre-deformation and applied stress on the heterogeneous nucleation at the boundary were also examined; C–N was always confirmed to occur at the tilt boundary, and the advantage of the boundary for nucleation of martensites did not change even under pre-deformation or applied stress. Furthermore, the martensite-start stress (σM) and the morphology of martensites in the stress-assisted transformation were strongly influenced by C–N. 相似文献
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Jian Zhang ) Jinguo Li ) Tao Jin ) Xiaofeng Sun ) Zhuangqi Hu ) ) Institute of Metal Research Chinese Academy of Sciences Shenyang China ) Graduate University of Chinese Academy of Sciences Beijing China 《材料科学技术学报》2010,26(10):889-894
A single crystal Ni-base superalloy was processed with withdrawal rates between 2 and 7 mm/min.The ascast microstructures,heat treatment response and creep property have been characterized as a function of the withdrawal rate.As expected,the primary and secondary dendrite arm spacing decreased with increasing withdrawal rate;microsegregation degree and porosity distribution were also varied with different withdrawal rates.The withdrawal rate of 2 mm/min resulted in a noticeable residual microsegregation eve... 相似文献
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用透射电镜和X-射线能谱仪对经自然和人工时效的18Cr2Ni4WA钢的微观组织、析出相及其分布进行了研究。结果表明,在应力作用下,组织的回复趋于不均,沿晶界析出的脱溶物增多。回复较充分的铁素体板条中析出粗大的(Fe、Cr)3C,局部均匀分布;回复不充分处,沿晶界还析出长杆状的(Fe、Cr)3C和更细小的杆状W2C。时效后组织中元素C、Cr和W趋于沿晶界偏聚,其中W几乎全部以碳化物的形式存在于晶界附近。析出相(Fe、Cr)3C的[001]晶带轴与α铁素体的[121]晶带轴近似平行。晶界脆性相的增多是该材料的螺栓在服役期间变脆和在腐蚀环境下失效的内在原因。 相似文献
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本文研究了凝固速率对单晶高温合金凝固界面形态、合金元素含量、γ’相及γ/γ’相界面结构的影响。结果表明,随凝固速率的减小,凝固界面从细枝、粗枝向胞状、平面转变,γ’相形成元素挥发严重,弥散分布的γ’相含量减少,γ’相严重合并粗化,γ/γ’相界面失去共格,亚晶界量减少。 相似文献
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Kai LIU Yiyin SHAN Zhiyong YANG Jianxiong LIANG Lun LU Ke YANG 《材料科学技术学报》2006,22(6):769-774
Effect of the heat treatment, including solution treatment (ST) and aging treatment (AT), on the prior austenite grain (PAG) size, microstructure and mechanical properties of a precipitation hardening maraging stainless steel was investigated. The results indicate that the relations between PAG size and yield strength (σy) under both ST and AT conditions obey the Hall-Petch relationship. Furthermore, after ST at 1050℃for 1 h cryogenic treated (CT) at -70℃ for 8 h AT at 535℃ for 4 h, the tested steel showed its ultimate tensile strength (σb) and σy over 1900 MPa and 1750 MPa, respectively. 相似文献
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通过对8型钛合金TM60进行不同制度的固溶时效处理,研究了各制度下其显微组织、相结构和力学性能的变化。研究结果表明:α相的含量和体积分数对合金性能有较大影响,固溶处理温度选择在700℃,时效处理温度应选择在400℃~450℃,β型钛合金TM60具有最佳的强塑性。 相似文献
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Haitao MA Haiping XIE Lai WANG 《材料科学技术学报》2007,23(1):81-84
The microstructure and melting behavior of Sn-9Zn-2Cu (SZC) lead-free solder with 3 wt pct Bi and various amount of Ni additions were studied. The wetting properties and the interracial reaction of Sn-Zn-Cu with Cu substrate were also examined. The results indicated that the addition of 3 wt pct Bi could decrease the melting point of the solder and Ni would refine the microstructure and the rod-shape Cu5Zn8 phase changed into square-shape (Cu, Ni)5Zn8 phase. The addition of Bi, Ni greatly improved the wettability of SZC solder. In addition, the interracial phase of the solders/Cu joint was typical planar Cu5Zn8 in SZC-3Bi-INi alloy. 相似文献
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The negative thermal expansion (NTE) properties of the antiperovskite manganese nitrides with micron-scale, submicron-scale and nanometer-scale microstructures, respectively, were investigated using the Mn3Cu0.5Ge0.5N composition as an example. It was discovered that the NTE start temperature, NTE operation temperature range and coefficient of NTE change obviously in a wide range with decreasing the grain size level of the microstructure. The mechanisms for the broadening of the NTE operation temperature range and the decrease in the absolute value of NTE coefficient were proposed based on the grain-size-dependence of the frustrated magnetic interactions and magnetic ordering. The present study indicates that the NTE properties of the antiperovskite manganese nitrides can be tailored by the control of the microstructure scale. 相似文献
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Xin GAO Yufeng ZHENG Wei CAI Su ZHANG Liancheng ZHAOSchool of Materials Science Engineering Harbin Institute of Technology Harbin China 《材料科学技术学报》2004,20(1):97-99
The microstructure, phase transformation, compression property and strain recovery characteristics of equiatomic TaRu super high temperature shape memory alloy have been studied by optical microscope, XRD, DTA, compression tests and TEM observations. When cooling the alloy specimen from high temperature to the room temperature,β(parent phase)→β′(interphase) →β"(martensite) two-step phase transformations occur. The microstructure at room temperature show regularly arranged band morphology, with the monoclinic crystal structure. The twinning relationship between the martensite bands is determined to be (101) of Type I. Reorientation and coalescence of the martensite bands inside the variant happened during compression at room temperature. The β′→β reversible transformation contributes mainly the shape memory effect, with the maximum completely recovery strain of 2%. 相似文献
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本文就晶化工艺对纳米双相复合永磁体的组织和磁性能的影响的研究进展做一综述,探讨了等温退火条件对纳米双相复合永磁体显微组织和磁性能的影响规律,发现传统的等温退火工艺对纳米复合永磁体的进一步发展具有较大的局限性,提出了几种新的制备纳米双相复合永磁体的晶化工艺. 相似文献
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Zhenya Zhang Huashun Yu Shaoqing Wang Haitao Wang Guanghui Min Key Laboratory of Liquid Structure Heredity of Materials Ministry of Education Sh ong University Jinan China 《材料科学技术学报》2010,26(2):151-155
This study investigated the microstructures and mechanical properties of ZK60 alloy prepared by a simplified rapid solidification powder metallurgy (RS P/M) processing system (S-RS P/M), which consists of warm press in dry air and hot extrusion. Microstructure characterizations showed that S-RS P/M alloy consisted of magnesium matrix and oxide stringers of~1 μm in width. TEM (transmission electron microscopy) observations illustrated nano-size magnesia particles (10-30 nm) constituted oxide stringer in deta... 相似文献
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The microstructures and hardness of pure Al samples subjected to plastic deformation with different tem- peratures and strain rates were investigated. The results showed that the strain-induced grain refinement is significantly benefited by increasing strain rate and reducing deformation temperature. The saturated size of refined subgrains in Al can be as small as about 240 nm in cryogenic dynamic plastic deformation (DPD). Grain boundaries of the DPD Al samples are low-angle boundaries due to suppression of dynamic recovery during deformation. Agreement of the measured hardness with the empirical Hall-Petch relation extrapolated from the coarse-grained Al implies that the low-angle boundaries can contribute to strengthening as effective as the conventional grain boundaries. 相似文献
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