Papers by Keyword: Diffusion Path

Abstract: Interdiffusion in two-phase Ni-Cr-Al diffusion couple was studied experimentally and simulated numerically. The diffusion multiples were prepared by hot isostatic pressing, HIP and post-annealing at 1200°C. The concentration profiles were measured with wide line EDS technique – a method suitable to study multiphases. Hence the diffusion paths were determined. The experimental profiles and diffusion paths were compared with numerical results simulated with application of the Darken bi-velocity method implemented to describe interdiffusion in a two-phase zone.

Abstract: Small spacing tunnel due to the special structure form and two tubes are only separated by a thin wall. This structure form is likely to cause secondary pollution, pollution gas discharged into the adjacent tunnel. This phenomenon will lead to increased ventilation system energy consumption. This paper analysis gas diffusion path between two adjacent tunnels, using CFD (Ansys Fluent). To relieve the pollution gases secondary pollution of tunnel portal area, using CFD analyzed gas diffusion path under different circumstances, for opening hole on the top of sunshades, extended of the wall between two adjacent tunnels and other programs, and identify more comprehensive disposal program.

Abstract: Interdiffusion plays a significant role in the formation and stability of metallic joints and coatings. It is also of critical importance in designing advanced materials. Because commercial alloys are usually multicomponent, the key target is prediction of a complex morphology of the diffusion zone which grows between the alloys, alloy-coating, etc. In a two-component system, the diffusion zone can be composed of single-phase layers of the intermetallic compounds and solid solutions. The evolution of the composition and thicknesses of such layers are fairly well understood and consistent with the phase diagrams. The situation is qualitatively different in multicomponent systems. For example, the diffusion zone in a ternary system can be composed of single-and two-phase sublayers. Their number and thicknesses depend on the initial conditions, i.e. composition, component diffusivities and geometry of the system. The usual way of presenting the sequence of the layers and their compositions is by drawing a diffusion path which is, by definition, a mapping of the stationary concentrations onto the isothermal section of the equilibrium phase diagram. The diffusion path connects initial compositions of the diffusion couple and can go across the single-, two-and three-phase fields. It starts at the composition of one alloy and ends at the other. The possibility of mapping the concentration profiles onto the ternary isotherm has been postulated in one from the seventeen theorems by Kirkaldy and Brown [] for the diffusion path. The detailed presentation of all theorems was recently done by Morral []. Here we remind the reader only of the chosen ones (shown in italics).

Abstract: A first-principle simulation of the surface diffusion of an extra metal (Me) adatom on the corresponding 1/3 monolayer (ML) Ge (111)√3×√3 Me induced surfaces has been performed. Using the Nudged Elastic Band (NEB) optimization method, the minimum energy paths and activation energy barrier profiles for all known Me inducing √3×√3 reconstruction on a Ge(111) surface have been obtained. The value of the activation barrier is shown to depend on the adatom formation energies and the atomic radius of the diffusing metal: 0.33 eV for Pb and 0.25 eV for Sn. The Arrhenius pre-exponential factors that were obtained in the harmonic approximation are as large as 10^11-12 Hz for all of the investigated surfaces, which supports the single-atomic diffusion model considered here.

Abstract: In this paper we couple the bi-velocity with the phase field method. It deals with: (1) the different mobility of the components in the two-phase zone; (2) nonzero steps of molar volumes for each component from phase to phase and (3) the composition dependent interdiffusion coefficients. The method allows to determine the average stress field during the diffusion process, the kinetics of the reactions and estimate the entropy production. The paper presents the numerical computations of diffusion in th eNiAlCr system. The results can serve as a basis in designing gradient coatings of extended life time.

Abstract: During sintering of Wbronze metal matrix composites, the difference in the interdiffusuion path, sintering atmosphere and alloying element might be the source of the swelling phenomenon. In this study, the factors lead to swelling of Wbronze sintered compacts were investigated. To achieve this goal, two swelled groupes of Wbronze sintered compacts were examined. The first group was compacts of ball milled powder with activator additions and the second group was compacts of ball milled powder infiltrated by bronze melt. The latter type showed the severest level of swelling. Sintered density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were incorporated to clarify and predict the reasons standing behind the swelling of the Wbronze sintered compacts. Key words: swelling, diffusion path, grain size, sintering activator

Abstract: The hybrid effect of Al and Cr in zinc bath on galvanizing coatings were studied by means of scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS), coupled with hot-dip galvanizing experiments. A new phase T1 was found in the coating, and the ζ phase was absent when hot-dip galvanizing at 480 °C. When Cr added zinc bath were alloyed with 0.1 wt.% Al, coating was composed of δ, ζ, η and T1 phases; when Cr added zinc bath were alloyed with 0.2 wt.% Al, δ phase layer became thinner, ζ changed from even layer to blocky crystals, and diffuse-Δ coexisted with the ζ phase. The morphology evolution of galvanizing coating was analyzed and the hybrid effect of Al and Cr were discussed with diffusion path theory.

Abstract: A thick film ZrO2-based NOx sensor feasible for diesel and gasoline engine applications has three diffusion paths, the size of paths has a great influence on sensor signal output. This paper studies the relationship between the pump current signal and the size of paths, the manufacture of NOx sensors of varied path sizes by the method of filling organics and then sintering at a high temperature to form a stable path, and detections of the sensors in a standard gas chamber. Then matching sizes of three paths are obtained.

Abstract: Ti, SiC and their composite materials have been widely used as high temperature structural material. The knowledge of interfacial stability between SiC and Ti is vital in high temperature applications. In this study, SiC/Ti diffusion couples were prepared to investigate the interfacial reactions between SiC and Ti at 1273 K. Phase forming sequence, microstructure and thermal stability of SiC/Ti interface were studied. It was indicated that after annealed at 1273 K for 10 days, 4 reaction layers were formed at the SiC/Ti interface. The diffusion path between SiC and Ti is SiC/Ti₃SiC₂/Ti₅Si₃/Ti₅Si₃+TiC/Ti₃Si/Ti. As the annealing time prolong, the thicknesses of these reaction layers increased.

Abstract: A new fabrication process was proposed for half-Heusler type TiNiSn thermoelectric alloys. Based on the result that the TiNiSn phase can be formed easily at the Sn(Liquid)/TiNi(Solid) interface, the liquid-solid reaction-sintering process was developed using TiNi and Sn powders. The TiNi compound powders were prepared by the atomization method using argon gas atmosphere. We have fabrictaed nearly single-phase TiNiSn alloys and evaluated their thermoelectrical properties; the presnt TiNiSn alloys have large electrical power factor of about 3.5 mWm-1K-2, and the maximum value of dimensionless figure of merit, ZT = 0.67, can be achieved at around 700 K even without tuning of the carrier concentration through alloying elements.