Phase growth in alpha brass with thin layer of electroplated zinc during homogenization annealing

Diffusion mechanism in between thin electroplated Zn coating and Cu – 37wt%Zn substrate during homogenization annealing substantially depends on electroplating parameters. Experiments carried out to determine phase growth and solute profile at various current densities reveal that the increase of current density tends to reduce phase growth. The coefficient of phase growth has been determined and is found to be dependent on the relative density of plating layer.

Flattening of Diluted Species Profile via Passive Geometry in a Microfluidic Device

In recent years, microfluidic devices have become an important tool for use in lab-on-a-chip processes, including drug screening and delivery, bio-chemical reactions, sample preparation and analysis, chemotaxis, and separations. In many such processes, a flat cross-sectional concentration profile with uniform flow velocity across the channel is desired to achieve controlled and precise solute transport. This is often accommodated by the use of electroosmotic flow, however, it is not an ideal for many applications, particularly biomicrofluidics. Meanwhile, pressure-driven systems generally exhibit a parabolic cross-sectional concentration profile through a channel. We draw inspiration from finite element fluid dynamics simulations to design and fabricate a practical solution to achieving a flat solute concentration profile in a two-dimensional (2D) microfluidic channel. The channel possesses geometric features to passively flatten the solute profile before entering the defined region of interest in the microfluidic channel. An obviously flat solute profile across the channel is demonstrated in both simulation and experiment. This technology readily lends itself to many microfluidic applications which require controlled solute transport in pressure driven systems.

Phase-Field Simulation of Double Dendritic Growth in Solidification of Binary Alloy with Forced Convection

A phase-field approach which incorporates mass and momentum and solute conservation equations for simulation of Al-Cu binary alloy solidification is studied. The effect of force convection on the double dendrite growth and solute profile during the solidification of binary alloy were investigated. The results indicate that dendritic grows unsymmetrically under a forced flow, the growth velocity of the upstream tip is faster than the downstream tip. The downstream tip of the first dendrite and the upstream tip of the second dendrite are influenced each other, the upstream tip of the second dendrite will Coarsen, and the concentration at the boundary between them is the highest. Moreover, the interaction between the two dendrites is more and more obvious with the increasing of the flow speed.

Microanalysis of Precipitate Free Zones (PFZ) In Al-Zn-Mg and Cu-Ni-Nb Alloys

Due to their possible detrimental effect on the stress corrosion and mechanical properties, Precipitate Free Zones (PFZ) in precipitation hardening alloy systems have been the subject of several investigations. Earlier studies by Nicholson and other workers convincingly demonstrated that PFZ can form as a result of vacancy concentration profile near the grain boundaries (1,2). Based on these and other investigations, PFZ in alloys are generally attributed as due to either solute depletion or vacancy depletion. Recently, several investigations have applied microanalytical techniques (plasmon loss, electron energy loss and X-ray microanalysis) to understand the solute profile in the PFZ particularly in the Al-Mg and Al-Zn-Mg systems (3,4). The present investigation was conducted to provide a better understanding of the formation of PFZ in alloys by analyzing the solute profiles in the PFZ by X-ray analysis in two alloys (5). One was an Al-2.2% Zn-4.7% Mg* alloy which has been demonstrated to form PFZ due to the vacancy concentration profile (1,2). The other alloy is a Cu-30% Ni-0.9% Nb alloy in which the PFZ was suggested to form due to depletion of Nb (6). Samples of these alloy samples were examined after selected heat treatments.