Solid State Phenomena Vol. 315

Abstract: The uniformity of temperature field distribution in creep aging process is very important to the forming accuracy of components. In this paper, the temperature field distribution of 2219 aluminum alloy tank cover during aging forming is simulated by using the finite element software FLUENT, and a two-stage heating process is proposed to reduce the temperature field distribution heterogeneity. The results show that the temperature difference of the tank cover is large in the single-stage heating process, and the maximum temperature difference is above 27°C,which seriously affects the forming accuracy of the tank cover. With two-stage heating process, the temperature difference in the first stage has almost no direct impact on the forming accuracy of the top cover. In the second stage, the temperature difference of the tank cover is controlled within 10°C, compared with the single-stage heating, the maximum temperature difference is reduced by more than 17°C. The two-stage heating effectively reduces the heterogeneity of the temperature field of the top cover. The research provides technical support for the precise thermal mechanical coupling of large-scale creep aging forming components.

Abstract: The porous ceramic filter material is the most effective filter materials in the integrated gasification combined cycle. The porous silicon nitride due to its higher mechanical strength, as well as good corrosion resistance, is considered as a promising material in the integrated gasification combined cycle, and it were prepared directly though the SiO₂ and α-Si₃N₄ through carbothermal reduction - pressureless sintering in nitrogen. There was a great lot weight loss in this reaction, so it was expected to create the high porosity materials. The rod-like β-Si₃N₄ grains and uniform pores were formed through changing the content of α-Si₃N₄, SiO₂ and C. So high-performance and porosity controlled porous silicon nitride filter material was obtained. With an increasing in the α-Si₃N₄ content, the weight loss, the linear shrinkage, and the porosity decreased, the flexural strength increased accordingly. The porous silicon nitride filter material with addition of 50wt% α-Si₃N₄ showed a higher aspect ratio β-Si₃N₄ grains and better mechanical properties .

Abstract: Ferrosilicon alloy has been commercially produced in an electric furnace at 1700 - 1750 °C, using quartz as a silica source. With an aim to reduce production cost, rice husk ash (RHA) had been introduced to the process as a silica source. The present study reports an in-depth investigation on the ferrosilicon alloy formation at 1550 °C via carbothermic reduction using RHA with coal and graphite. Blend A: RHA/Fe₂O₃/Coal and B: RHA/Fe₂O₃/Graphite were prepared according to the C/O molar ratio of 1/1. The well-mixed samples were compacted into a pellet and then heated at 1550 °C in the tube furnace for 30 and 60 minutes while the argon flowing at the rate of 1 L/min. XRD and SEM results show that the bulk metal mainly composes of FeSi phase, while SiC and other slag phases adhere at the surface of the droplet. Characteristics of the carbonaceous materials, especially ash oxides content affect the kinetic of ferrosilicon formation. Silicon concentration in the produced metal droplets was measured using an ICP technique. For blend A, Si content in the metal was 18.3 wt% and 81.9 wt% after 30 and 60 minutes, respectively. While, Si recovery in the metal for blend B reached 88.4 wt% since 30 minutes. The experimental results show that the production of ferrosilicon alloy from RHA can be produced at 1550 °C, which the temperature lower than that of the commercial method by 150-200 °C. The finding in this research is beneficial for ferrosilicon and agricultural industries and thus promotes the sustainable steelmaking industry.

Abstract: The effects of cast and heat treatment processes on microstructure and mechanical property of K4169 alloy have been investigated. The results show that low shell and pouring temperature can significantly improve the room temperature tensile and elevated temperature stress-rupture properties of the alloy; The joint function of hot isostatic pressing (HIP) and homogenization+solution+aging (HSA)standard heat treatment can effectively close casting defects such as micro-looseness, significantly improve the segregation of the alloy structure, basically eliminate the Laves phase, only a small amount of MC carbide dispersed in the grain boundary and short rod-shaped δ-phase. What is the most significant is that a large number of lenticular γ'' phases are uniformly precipitated, Which enhance the microstructural stability, and significantly improve the room temperature tensile properties and high temperature endurance properties of K4169 alloy.

Abstract: Creep age forming technology (CAF) has been widely used to manufacture large integral panels in aerospace industry. However, due to the bending of the sheet metal, the stress states usually changes along the thickness direction during the CAF process, resulting in a complex distribution of stress. In addition, deformation texture is introduced when the sheet has a large pre-deformation, which also greatly affects the shape and performance of the component after aging. In this paper, the anisotropy in compression creep-ageing behavior of 2219-T3 aluminum alloy was studied. It was found that there is obvious anisotropy of compressive creep strains, the creep strain is the largest when the applied stress is along the rolling direction (RD) and the smallest when the applied stress is along the transverse direction (TD). The results of room temperature (25 ° C) and high temperature (165 ° C) tensile property test shows that the as-received material properties has obvious in-planar anisotropy, and the yield strength in the RD is the largest, but the 45° and TD are basically the same. Interestingly, the anisotropy of yield strength after SFA and compressive stress creep aging has basically disappeared, that is,the material properties tended to be isotropic after ageing.

Abstract: 2195 Al-Li alloy is famous for high strength, excellent fatigue strength and good stress corrosion resistance, which is widely used in the manufacture of high-performance aerospace components. The aim of this study is to validate how the stress relaxation aging behavior effect on the mechanical properties of 2195 Al-Li alloy. Through mechanical property test, the research was found that the performance after stress relaxation aging is higher than artificial aging (AA). In addition, the analysis of scanning electron microscopy SEM and TEM revealed that dislocations should be introduced by the stress relaxation aging process, which is more conducive to the precipitation of the T1 phase and strengthened the material with prolong ageing time. The results show that stress relaxation aging can significantly promote the precipitation of the T1. Therefore, this paper sheds new light on how SRA can improve mechanical properties and that SRA make better improve the distribution of precipitates in the grain boundary.

Abstract: Vibration systems require the damping materials operating at high service temperature. In this paper, damping performance of HT100, M2052 and S316L at 350K were evaluated by applying different frequencies, strain amplitudes and heating rates. It is found that the internal friction dependence of frequency of HT100, M2052 and S316L all show a characteristic of Check function, and the resonance frequency has a negative linear correlation with the material physical parameters. The strain amplitude as well as heating rate has no obvious effect on the resonance frequencies of the materials, but significantly enhance the internal friction of the interface damping alloys such as M2052 and HT100, but small on single-phase alloys such as S316L. The internal friction mechanism for HT100 and M2052 are of static hysteresis at 350K, and HT100 and M2052 are applicable candidates for working at temperatures around 350K from the viewpoint of vibration reduction.

Abstract: Due to the temperature and concentration determine the kinetic undercooling of interface growth and nucleation undercooling inside the melt, they play an important role in the solidification microstructure of the alloy. In this paper, the effect of temperature gradient and cooling rate on the dynamic undercooling was studied and the mechanism of the concentration at the solid-liquid interface on the kinetic undercooling during the continuous cooling process was analyzed. A calculation method for the coupling of temperature and concentration during Inconel 718 alloy solidification was developed, which can solve the problem that the concentration and temperature are difficult to be calculated at the same time in the numerical calculation.

Abstract: The influences of third alloying element on the internal friction behavior and the mechanical properties in the water quenched Ti-12Mo alloys were investigated using multifunctional internal friction apparatus and mechanical testing machine, respectively. The two relaxational internal friction peaks that are named as P1 and P2 peaks were found in the water quenched Ti-12Mo alloys. Third alloying element has influences on the P1 and P2 peaks. In addition, the young modulus and yield strength are also influenced by the addition of Third alloying element.