Low carbon steel plays an important role in many applications due to its high strength. Its high strength comes from the strengthening effect of nano-Cu-rich phase precipitates. In order to effectively adjust the microstructure of Cu-rich phase precipitates and obtain Fe-Cu-based steel with the best properties by adding different alloying elements (Mn, Al), it is necessary to understand the precipitation process of Cu particles. In this paper, based on the Ginzburg-Landau theory, the previous phase field model is modified, and the continuous phase field method is used to simulate the precipitation mechanism of nanometer Cu-rich precipitates and the inhibiting of the effect of Al content on Cu-rich precipitates of Fe-15%Cu-3%Mn-<i>x</i>Al (<i>x</i> = 1%, 3%, 5% mass fraction) alloy at 873 K isothermal aging. Combining with the free energy derived from thermodynamics database, the microstructure evolution corresponds to the real alloy system. By calculating the composition field variables and structural order parameters, the evolution of phase separation and precipitated phase morphology in aging process are simulated. Moreover, the influence law of morphology, quantity density, average particle radius, growth and coarsening of Cu-rich precipitated phase are discussed. The results show that in the early stage of aging process, the nano-Cu-rich phase precipitates through the spinodal decomposition mechanism, and is randomly distributed in the iron matrix. Furthermore, due to the difference in atomic diffusion rate, the core-shell structure with Cu-rich phase as a core is formed. With the aging time extending, the structure of Cu-rich phase precipitates changes from bcc to fcc. Because of the synergistic effect between Al and Cu, the diffusion of Cu is slowed down. Besides, with the Al and Mn atoms precipitating, Al/Mn clusters are segregated around the Cu-rich precipitates, forming the Al/Mn intermetallic core-shell structure, and gradually wrapping the Cu-rich phase uniformly. During the evolution of the precipitation stage, the Al/Mn clusters are isolated around the Cu-rich precipitation phase, forming a gradually uniform Al/Mn intermetallic phase core shell structure covering the Cu-rich phase, which is to hinder the buffer layer from forming in the precipitation stage of the reservoir. In addition, with the Al content increasing, the Al/Mn intermetallic phase promotes the growth of the buffer layer and hinders the Cu-rich precipitate phase from growing and coarsening.
SiC films were prepared on Si(111) substrates by annealing polystyrene gel films at temperature 950℃ in vacuum(10-3 Pa).Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD), Transmission electron microscopy(TEM).Raman scattering and X-ray photoelectron spectroscopy(XPS) were used to study the morphology of the surface, crystal structure. composition and chemical state of the element of the SiC films. It revealed that the films consisted of preferentially oriented crystalline 6H-SiC epilayer which grew along(0001) planes parallel to Si(111) planes. The ratio of Si to C was about 1 and there were some carbon and oxide contaminant species in the form of CH, CO and Si2O3 along with a small amount of adsorptive oxide at the surface of the films. The polycrystalline grains in the films grew cylindrically along c axis.Their maximum size was about 150nm. The film was smooth. dense and uniform with a thickness of about 0.3 μm. It was found that covering the polystyrene film with a Si plate could increase the quantity of SiC during anncaling.
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