Functional and Functionally Structured Materials II

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Authors: Ting Biao Guo, Chen Wang, Qi Li, Feng Zhang, Wan Wu Ding
Abstract: As a kind of refining agent, Al-Ti-C-Ce intermediate alloy is widely used in the field of nonferrous alloy smelting. The effect of Al-Ti-C-Ce contents on microstructure and properties of Al-Cu-Mn alloy was studied by OM, SEM, EDS and other test methods. The results show that the as-cast microstructure of Al-Cu-Mn alloy is obviously refined after adding 0.1% Al-Ti-C-Ce, and the θ phase is characterized with the shape of point or strip. With the increase of the addition amounts, parts of the grains coarsened. When the addition amount reached to 0.3%, the refinement effect of the alloy microstructure was further reduced, and the number of intergranular precipitates TiC and Al3Ti increased. Ductile fracture is the main failure mode of the alloy. After T6 heat treatment, the grain size changed little, and the number of θ phase, TiC and Al3Ti decreased, changed from the mesh to the point or needle or strip structure, and the proportion of alloy ductile fracture increased. The addition of Al-Ti-C-Ce has positive effect on improving the microstructure and properties of Al-Cu-Mn alloy.
Authors: Ting Biao Guo, Qi Li, Chen Wang, Shi Ru Wei, Yi Bo Wu
Abstract: The evolution of microstructure of ZL205A alloy during equal channel angular pressing (ECAP) by route A at room temperature was investigated by OM, SEM and XRD, and the hardness of cast and heat treatment alloy from different strain were tested. The results showed that the grain of cast alloy were obviously refined, the massive q phase along the grain boundary were crushed, and prompts the distribution of q streamline after one pass through ECAP. After two passes of ECAP, the distribution of q phase is more uniform. After heat treatment through ECAP, the grains were also obviously refined, and elongated in axial direction, which also prompts the distribution of q streamline. The hardness was significantly improved after ECAP. The hardness of cast alloy increases from 65HV to 132HV after two passes, and that of heat treatment alloy increases from 112HV to 198HV. With the increase of extrusion passes, the number of dimples gradually increased and evenly distributed, the depth of dimples was of a similar level, and the distribution of precipitated phase is more uniform.
Authors: Yu Wang, Yun Lai Deng, Jin Zhang, Yong Zhang, Xin Ming Zhang
Abstract: This Paper studied the precipitation behaviour and creep deformation of 2124 aluminum alloy based on the concept of complex field. A mechanical vibration field was introduced into the creep aging forming process of 2124 aluminum alloy, and its effects on creep deformation, precipitations behaviour and mechanical properties under the condition of double curvature loading and aging temperature were investigated by three-dimensional scanning technique, TEM and tensile test, respectively. The results showed that the spring back value along the rolling and transverse direction presented after creep aging forming were reduced by 25% and 15% respectively. The volume fraction of precipitates increased and distributed more densely and uniformly. Meanwhile, the yield stress improved by 15MPa and the degree of anisotropy decreased by 17% with mechanical vibration field applied to the manufacturing process.
Authors: Shao Chen Zhang, Zhi Bin Wang, Yun Fan Dong, Kang Wang, Qi Wang, Jin Feng Leng
Abstract: The effect of aging treatment on the aging hardening of 0% Yb and 0.4% Yb modified A356.2 alloy was investigated by hardness measurements and optical microscope. In this work, A356.2 was first subjected to 535°C for 5h and then subjected to 150°C, 180°C for 2h-12h hours. Results show that during aging process, there was a hardness peak along the increasing of aging temperature and time. With increasing aging progress, the morphology of Si phases became shorter and spherical. After optimum time, Si phases was coarse and the dendritic grain was broken. The peak-aged of unmodified alloys was 150°C for 10h and 180°C for 6h,and corresponding hardness values were 62.35HB and 77.10HB, respectively. With Yb addition, the hardness reached 87.58HB and 98.28HB on peak aging of 150°C/8h and 180°C/ 6h, respectively. The greatest degree of hardness was increased by 40.46% and 27.47%, combined with no Yb addition. XRD shows the interplanar crystal spacing of A356.2 with 0.4% Yb addition, which was larger than fresh A356.2 alloy. When adding 0.4%Yb under 180°C for 6h aging progress, the ultimate tensile strength was 284 MPa 12.7% increasing compared with former work.
Authors: Guang Yang, Hong Chao Kou, Jin Shan Li, Heng Zhi Fu
Abstract: An experimental platform for controlled solidification and heat treatment and its applications in TiAl alloys are reported. The controlled solidification facility can be used to study the microstructure evolution of metals and alloys during solidification process and the controlled heat treatment device can realize the complex heat treatments and high temperature quenching conveniently. Compared with the traditional experimental equipments, this platform has three advantages. First, it can precisely control heating and cooling speed as well as isothermal holding time during solidification and heat treatment. Second, the high temperature microstructure can be obtained by quenching with high accuracy. Third, these two devices are cheaper and suitable to use in laboratory.
Authors: Zhang Guang Liu, Pei Jie Li
Abstract: Ti55 is a type of new near-α titanium alloy featuring good heat resistance and thermal stability at a temperature below 550°C. This paper explores the superplastic behaviors of Ti55 titanium alloy sheets at high temperature. The results showed that at a strain rate between 8.3×10-4 and 1.32×10-2s-1 and a deformation temperature between 885 and 935°C, this material exhibited favorable superplasticity. A 872% tensile elongation was achieved even at a high temperature of 925°C and a high strain rate of 1.32×10-2s-1. For a deformation temperature of 925°C and a strain rate range of 8.3×10-4~1.32×10-2s-1, the strain rate sensitivity index (m) was equal to or higher than 0.38, which depends on the specific strain rate and reached its peak at 6.64×10-3s-1. The study showed that tiny cavities tended to appear around the rare earth phase particles. As the deformation temperature and the deformation strain rate increased, both size and volume fraction of the cavities decreased significantly. When the plastic deformation further increased, the cavities experienced not only longitudinal aggregation along the tensile strain direction, but also transverse aggregation normal to the tensile strain direction. The typical high-temperature ductile fracture morphology is related to both aggregation and growth of the large number of microscopic cavities and dimples.
Authors: Qing Yun Zhao, Si Rui Cheng, Li Dong Wang, Li Min Dong, Feng Lei Liu
Abstract: The effects of heat treatment on microstructure and mechanical properties of Ti-38644 alloy were investigated by scanning electron microscope (SEM) and transmission electron microscopy (TEM) as well as uniaxial tensile test. The results show that when the solution temperature is lower than 845°C, the microstructure of Ti-38644 alloy is equiaxed β phase with the grain size of 20μm, and the tensile strength is about 960MPa. As raising solution temperature to 860°C, the grain size of Ti-38644 alloy increases to 100μm and the tensile strength decreased to 870MPa. There are a large number of secondary α phase precipitated from the grain boundaries and within grain of β phase undergoing aging treatment. Secondary α phase coarsens with increasing the aging temperature, leading to the decrease of tensile strength. After solution treatment at 815°C for 1.5h, water quenching plus aging at 520°C for 10h, air cooling, Ti-38644 alloy shows a better mechanical property with the tensile strength 1330MPa, elongation and reduction of area 10% and 45% respectively.
Authors: Yang Jie Tang, Yong Zhong Zhang, Yan Tao Liu, Wei Pan
Abstract: Laser additive manufacturing (LAM) technology was applied to prepare Ti-22Al-25Nb alloy thin-wall sample. The characteristics and evolution mechanism of solidification microstructure were investigated, and the tensile properties at horizontal and vertical directions were discussed. The results indicated that the solidification microstructure in single deposition layer evolved as: plane crystal structure, cellular crystal structure, columnar dendrite structure and equiaxed dendrite structure, from the bottom to the top of the molten pool. During the solidification process, the temperature gradient and solidification velocity decided the grain growth morphology. However, the grain of the as-deposited materials grew up to thick equaxied structure when the upper layer was forming. The tensile properties at horizontal and vertical directions were not much different, both of these exhibited high strength and low ductility.
Authors: Ya Qian Yang, Bo Chen, Meng Shu Zhang, Ying Che Ma, Kui Liu
Abstract: In metallurgical production processes, the vapor pressures and activity coefficients of impurity elements areconsidered as importantparameters in thermodynamic calculation. A saturated flow method was used to measure the dissolution equilibrium of Mn vapour over the surface of liquid Ni-Cr-Co-Mo alloys from 1773 to 1923K, and the measured results were employed in the calculation of the activities andactivity coefficients of Mn in liquid Ni-Cr-Co-Mo alloys. It is found that Mn showed a strong positive deviation from the Henry’s law, and the relationship between temperature and the standard free energy of dissolution reaction Mn(g)=[Mn]Ni-Cr-Co-Mowas determined to be . At 1873 and 1923K , the activity coefficient ƒof Mn in the Ni-Cr-Co-Mo alloymelt with 0.2wt.%Mn addition were calculated to be 1.065 and 1.068, respectively. According to the results mentioned above,the volatile lower limit of Mn can be up to 2.14 ppm in conventional vacuum melting production.
Authors: Wen Yong Xu, Zi Chao Peng, Mu Zi Li, Minh Son Pham
Abstract: Microstructure analysis of Ni-based superalloy FGH96 under different ageing treatments were carried out in order to understand the microstructure-creep strength relationships of the alloy. It was found that the volume fraction of tertiary γ′ and the mean γ-channel width was significantly varied with different ageing treatments, leading to the changes in creep behavior. The dislocation/γ′ shearing mechanisms were also changed with ageing treatment. The volume fractions of both secondary and tertiary γ′ and the mean γ-channel width were quantitatively analyzed by electron microscopy. The quantified microstructures were used for a crystal plasticity-based constitutive model. It was observed that the crystal plasticity model can accurately simulate experimentally observed creep behavior of aged samples showing significant secondary creep stage.

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