Papers by Keyword: Diffusion Kinetics

Abstract: Multicomponent diffusion in metallic melts is a very important phenomenon during the solidification/casting process of the metallic alloys. However, there exist extremely limited reports on the diffusivity information in multicomponent metallic liquids. In this chapter, a universal and effective phenomenological approach to predict the composition– and temperature–dependent diffusivities in liquid multicomponent systems is systematically proposed. The presently proposed phenomenological method is then adopted to construct the diffusivity/mobility databases of liquid solders, cemented carbides, Co–Cr–Fe–Mn–Ni high entropy alloys and Al–Ce–Ni alloys. Then, the accurate diffusivity/mobility data are further utilized to perform the simulations of the dissolutions of the substrate into the solders, the gradient layer formation of the cemented carbides, the diffusion behavior of liquid Co–Cr–Fe–Mn–Ni high entropy alloys and the rapid solidification of Al–Ce–Ni system. The simulated results indicate that the presently proposed phenomenological method is applicable to investigate the diffusion kinetics in multicomponent metallic melts.

Abstract: Mg and Al were bonded successfully by means of diffusion bonding using Ni interlayer. The microstructure, diffusion mechanism and regulation of atom diffusion were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron probe microanalysis analysis (EPMA). The results showed that the joints consisted of Mg-Ni interface and Al-Ni interface, and there were Mg₂Ni formed in the Mg-Ni interface and Al₃Ni formed in the Al-Ni interface, respectively. Diffusion activation energy of Mg and Al were lower than that of Ni in the Mg-Ni and Al-Ni interface. The thickness (x) of Mg₂Ni and Al₃Ni can be expressed as x²=3.97×10^-4 exp (-139600/RT) (t-t₀) and x²=8.62×10^-3 exp (-174200/RT) (t-t₀) with heating temperature (T) and holding time (t).

Abstract: In order to detect the diffusion law of alloying elements in 0.95c-1.45cr-0.35mn-0.25si bearing steel during annealing process,the database of tcfe7 and mobfe of dictra software were used to calculate the diffusion kinetics. The results show that c atoms diffuse rapidly in single fcc phase field and at last uniform,temperature and holding time have no significant influence on them;cr,si,and mn has the same diffusion mechanism,the initial solidifying field has lower solute than the subsequent,and has slight change after solidification. The improvement of segregation factor (cr) at 1300°C for 5h is better than at 1050°C, 1200°C for 10h.

Abstract: In this article moisture diffusion characterization of carbon fiber based polymeric composites (5428/CCF300 and 5405/CCF300) under recurrent hygrothermal ageingis investigated experimentally and numerically. Diffusion kinetics is studied by using Fickian and Langmuir diffusion models. Composite interface surfaces were closely studied by electron microscopy during the absorption/ desorption process, which revealed that micro-crack near weak interface provide passages for water diffuse.To simulate harsh service environment, understudied specimens were go through high humidity and high temperature (85°C and 120°C) conditions and then interlaminar shear strength (ILSS) properties of composites were determined. This study found that the interface property has effect on absorption/ desorption behaviour as well on ILSS. Validation of experimental results is carried out by using finite element analysis. In sum, this research attempts to analyze the behavior of carbon fiber composites underre current hygrothermal environment for the purposes oflong-term service prediction.

Abstract: The experiment has taken composite algorithm of cold rolling to prepare copper and aluminum composite laminate, studied the influence of diffusion heat treatment on the interface of copper and aluminum composite laminate. After Analyzed the relationship between the thickness of diffusion layer and diffusion heat treatment parameters, the experiments show that diffusion heat treatment temperature and diffusion time has influence on formation and size of the diffusion layer. At the same heat treatment temperature, the thickness of diffusion layer has parabolic relation with diffusion time with diffusion time extending and thickness of diffusion layer increasing. And the thickness of diffusion layer is increasing at the same heat treatment time. And the thickness of diffusion layer has exponential relation with diffusion heat treatment temperature. Quantitative analyzed the relationship between diffusion heat treatment parameters and diffusion layer thickness, and established a formula to describe the interface thickness and diffusion of heat treatment temperature and time.

Abstract: General description of the interplay between the Kirkendall shift (as a special way of relaxation) and diffusion induced driving forces in diffusion intermixing of binary systems is given. It is shown that, if the Kirkendall shift is negligible, a steady state Nernts-Planck regime is established with diffusion coefficient close to the slower diffusivity, independently of the type of the diffusion induced field and also independently whether this is a single field or a combination of different fields (e.g. stress field and extra chemical potential of non-equilibrium vacancies). Deviations from parabolic kinetics are expected only before or after this steady state stage. Using the results of our previous paper, on development and relaxation of diffusion induced stresses, it is illustrated that the setting of time of the Nernst-Planck regime is very short: intermixing on the scale of few tenths of nanometer is enough to reach it. It is also illustrated that this stage is realized even in the case of asymmetric interdiffusion (in one side of the diffusion zone the diffusion is orders of magnitude higher than in the other), when the stress distribution has a more complex form (having a sharp peak at the interface). Surprisingly the steady state is longer than it would be expected from the relaxation time of Newtonian flow: This is so because the composition profile is not static but changes fast in the timescale of the stress relaxation, and thus the stress re-develops continuously.

Abstract: Oxidation of SiC powder was studied at 1373 K to 1873 K in Ar-O2, Ar-H2O, and Ar-O2-H2O using thermogravimetry. At 1373 K to 1573K, the weight gain increased with increasing water vapor pressure. The oxidation rate was evaluated on the basis of the Ginstering-Brounshtein kinetic model. In this temperature region, the apparent activation energy for the oxidation was almost the same (139-191 kJmol-1) independent of the atmosphere, suggesting that the same oxidation process proceeds. On the other hand, at temperatures >1673 K, the weight gain in the dry O2 (Ar-O2) was greater than that in the wet and wet O2 (Ar-H2O and Ar-O2-H2O). The apparent activation energy in the dry O2 (442 kJmol-1) was much greater than that in the wet and wet O2. We propose that water molecule diffused in silica layer in the wet and wet O2 atmosphere at 1373 K to 1873 K.

Abstract: Aluminum spray coating was applied onto AZ91D magnesium alloy. The effects of post heat treatment on the interfacial characteristics, especially the diffusion kinetics of magnesium and aluminum atoms across the interface were studied in this paper. It was observed that there was an obvious interface between the aluminum coating and the magnesium alloy substrate. It was found that post heat treatment could reduce the number of pores existed in the aluminum coating. The post heat treatment resulted in not only the change in the composition and microstructure of the aluminum coating, but also the improved metallurgical bonding between the coating and the substrate.