Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Amorphous alloy composite is designed to prevent rapid propagation of shear bands in amorphous phase by introducing the second crystalline phase, which can improve the plasticity of alloy. In situ formed amorphous alloy composites have attracted much interest due to excellent properties and extensive application prospect, especially the dendrite reinforced amorphous alloy composite with excellent tensile plasticity. Recent studies show that the plastic deformation behavior of amorphous alloy composite is not only related to the mechanical properties of the crystalline phase, such as elastic modulus, but also with the size, volume fraction and morphology of the crystalline phase. In addition, the mechanical properties, especially the plastic deformation ability, of amorphous alloys are closely related to topological morphology of the samples, such as aspect ratio. For the amorphous alloy composite, the relationship between mechanical properties and topological morphology of the samples are of interest. In this work, by adjusting preparation process and size of the samples, the effect of cooling rates and aspect ratios on the mechanical properties of Ti45.7Zr33Ni2.9Cu5.9Be12.5 amorphous alloy composites were systematically studied. As decreasing the cooling rate during the preparation process, the sizes of dendrites in the amorphous alloy composites increases. And the crystalline phase presents evolution from branchlets to coarse dendrite. As the cooling rate decreases, strength of the composite decreases while plasticity increases. Moreover, different from the previous reports, the mechanical properties of amorphous alloy composite are not sensitive to the aspect ratio. It is attributed to the existing of the dendrites phase and deformation- induced phase transformation in the dendrites, which may adjust stress distribution of the amorphous alloy composites during deformation process.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： GH4169 superalloy is one kind of important metallic materials used for manufacturing turbine discs in aero-engine. In order to meet the demand of higher strength, high ratio alloying elements have to be added, resulting in the complex microstructure evolution during the long- term service at elevated temperature. Furthermore, the turbine disc usually bears overloading which will lead to the low cycle fatigue (LCF) damage in real working and result in fatal security problem. Besides, it is meaningful to decide the relationship between the microstructure evolution and performance degradation. In the present work, microstructure evolution and LCF behavior of GH4169 alloy during long- term aging were investigated. The microstructure evolutions of GH4169 alloy during long-term aging at 750 ℃ for 500, 1000, 1500 and 2000 h and the influences of long-term aging on the LCF behavior were investigated. The results show that the size of g ″ phases increases and the volume fraction decreases with the increase of aging time, compared with the increase of both size and volume fraction of d phases. Both the fatigue strength and fatigue life of the alloy decrease with the increase of aging time. For the specimen aged for the same time, the cyclic stress firstly contributes to cyclic hardening, then cyclic stability, and finally cyclic softening with the increase of cyclic numbers. It is found that the decrease of cyclic stress contribution is slightly effected by the size of g ″ phases increase and volume fraction decrease after long-term aging. Therefore, the LCF life of the alloy decreases since the crack easily propagates along with the long needle-like d phases and the g ″ phases precipitate free zones.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： GH4169 alloy is widely used to make aero engine, gas turbine as it is one of the most important superalloy. g'' phase is the main strengthen phase, however, the metastable g'' phase will transform to stable d phase during aging or servicing for certain time. d phase is significance in the alloy, its precipitating and distributing behavior have an effect on the properties of the alloy. In recent year, researchers pay more attention on electric field treatment (EFT), this is because of high energy density, accurate controlling, clean and safety. EFT is one of the most important energy field except temperature field and stress field. In this work, EFT was performed on GH4169 superalloy to investigate the influence of EFT on precipitation behavior of d phase in the alloy, and the mechanism of the effect of EFT on the phase transformation was also discussed. The results show that d phases precipitate on the grain boundaries after EFT with 8 kV/cm at 850 ℃ for 15 min, and large amounts of g'' phases precipitate inside the grains. With the increasing of EFT time, both the volume fraction and the size of d phase increase, at the same time the size of g'' phase increases. The volume fraction of d phase is less and the size of d phase is smaller, and the volume fraction of g'' phase is higher by EFT, compared with that by aging treatment (AT) for the same time. In addition, the Nb content on the grain boundary decreases and both Fe and Cr content increase, meanwhile the lattice parameters of c decreases and a, b increase. The vacancy concentrations can be accelerated by EFT, so that the diffusion of Fe and Cr atoms can be promoted. Meanwhile, the Nb atoms in d phases on the grain boundaries can be displaced by Fe atoms and Cr atoms, therefore the Nb atoms are dissolved into the grain. The nucleation rate of g'' phases increases with the increasing of vacancy concentrations. The vacancies relax coherent distortion between g phases and g'' phases, and suppress g'' phases to transform to d phases. Thus the stabilization of g'' phases is enhanced.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Cold-draw molybdenum wires with diameters of 125, 140 and 160 mm were selected as a model material. Tensile tests and tension-tension fatigue tests under stress control were conducted to investigate mechanical performance of the micron- sized Mo wires. While the fractured surfaces of the wires were examined by scanning electron microscopy. The experimental results show that both of tensile and fatigue strengths under stress control decrease with the decreasing wire diameter. The size effect on fatigue performance of the Mo wire can be attributed to the difference of the quantity of grains along the radial direction, which leads to that the smaller the wire diameter the more sensitive to the fatigue crack or defect on the Mo wire surface, and thereby, the shorter the fatigue life.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Evolution of drawing texture for A6 aluminum conductor with the drawing process was investigated by macro and micro-texture analysis. The results show that the fiber-like deformation texture of <111> and <100> formed in the drawing process, and <100> texture reduced while <111> texture enhanced with the increasing strain. The distribution of deformed texture was of homogeneity along the radial direction of wire: the deform texture transformed from strong <100> texture (~52% volume fraction) in the surface to strong <111> texture (~55%) in the center by moderate strains; the radial gradient texture was weakened and a strong <111> texture (>70%) formed in the overall wire by high strains. Moreover, the core hardness of the wire was higher than that of the surface, which attributed to the texture gradient distribution along the radial. Adjusting the drawing process to optimize the dislocation density and texture as well as their distribution in the wire is an effective route to improve the strength and conductive properties of the A6 aluminum conductor.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：采用热模拟实验研究了定向凝固与等轴晶U720Li合金的高温塑性变形行为,利用OM,SEM和EBSD分析了不同变形条件下合金的组织特征及动态再结晶机制.结果表明,定向凝固与等轴晶合金的变形抗力均随变形温度升高而降低.定向凝固U720Li合金沿垂直柱状晶方向变形时变形抗力较低,枝晶间协调变形能力良好,未出现裂纹.与等轴晶合金相比,相同变形条件下定向凝固合金的动态再结晶组织均匀;高温塑性变形过程中,定向凝固合金的动态再结晶主要以晶界弓弯和位错塞积方式形核.定向凝固U720Li合金的变形激活能为766 kJ/mol,比等轴晶合金降低了38.6 %,定向凝固合金呈现出更好的热加工特性.
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