Jae Chul Lee

Prediction of Si contents to suppress the formation of Al4C3 in the SiCp/Al composite

Abstract Interfacial phenomena in the SiC p /Al composite were investigated using SEM, DSC, AES, and XRD. The value of these combined techniques in elucidating detailed interfacial phenomena was demonstrated. Theoretical calculations of equilibrium Si contents required to prevent the formation of Al 4 C 3 in the SiC/Al composite were performed by taking the variations in Al and Si activities as well as those of other compounds into account for the calculations. Based on calculations, there exists a transition temperature at which a sudden increase in equilibrium Si contents required to prevent Al 4 C 3 formation occurs. Experimental measurements of equilibrium Si contents were also performed to confirm the theoretical results.

Controlling the textures of the metal strips via the continuous confined strip shearing(C2S2) process

Abstract A new concept process, a so-called as C2S2 process based on equal channel angular pressing, for fabricating the A1 alloy sheets with a high formability is introduced. The C2S2 machine was designed so that it can feed the metal strip in a continuous manner at a relatively high speed in the range of ∼20 m/min. A significant amount of the shear deformation could be achieved by passing the sample through the ECAP die with Φ = 120°. The pole figures were calculated both to demonstrate the evolution of the textures of the 1050 A1 alloy sheets and to elucidate the feasibility of the proposed process as a means for enhancing the formability of the metal strips.

Control of the interface in SiC/Al composites

Interfacial characteristics in metal matrix composites reinforced with ceramic reinforcements (MMCs) play a significant role in determining the mechanical properties, such as strength, ductility, toughness, fatigue, etc. To achieve superior mechanical properties in MMCs, it is essential to form adequate interfaces, which not only do not degrade the reinforcement during fabrication, but also retain the structural stability both for corrosive environments and at elevated temperatures. The objective addressed in the present work is to study a methodology to control the interfacial microstructures in the SiC/Al composite. Assessment of the stability of the newly formed interface at elevated temperatures was also made.

Texture evolution of the strip cast 1050 Al alloy processed by continuous confined strip shearing and its formability evaluation

Abstract Studies on texture evolutions were conducted on strip cast 1050 Al alloy sheets to assess the feasibility of equal channel angular pressing (ECAP) and subsequent heat treatments as a means for enhancing the formability while reducing the earing of the sheets. ODFs were calculated to investigate texture evolutions due to ECAP and subsequent heat treatments. The r -value and Δr-value were determined based on the measured pole figures to judge the formability and the earing of the samples. Experiments showed that the production of the 1050 Al alloy sheets with high formability ( r =1.05) and low earing (Δr=0.05) could be possible by ECAP and the heat treatment at appropriate temperature.

Interdimensional universality of dynamic interfaces

Despite the complexity and diversity of nature, there exists universality in the form of critical scaling laws among various dissimilar systems and processes such as stock markets, earthquakes, crackling noise, lung inflation and vortices in superconductors. This universality is mainly independent of the microscopic details, depending only on the symmetry and dimension of the system. Exploring how universality is affected by the system dimensions is an important unresolved problem. Here we demonstrate experimentally that universality persists even at a dimensionality crossover in ferromagnetic nanowires. As the wire width decreases, the magnetic domain wall dynamics changes from elastic creep in two dimensions to a particle-like stochastic behaviour in one dimension. Applying finite-size scaling, we find that all our experimental data in one and two dimensions (including the crossover regime) collapse onto a single curve, signalling universality at the criticality transition. The crossover to the one-dimensional regime occurs at a few hundred nanometres, corresponding to the integration scale for modern nanodevices.

Effect of various processing methods on the interfacial reactions in SiCp/2024 Al composites

Abstract SiC p /2024 Al composites were prepared using various processing techniques, such as spray forming, powder metallurgical hot pressing, thixoforming, and compocasting. The interfacial characterizations of these composites were performed using scanning electron microscopy, Auger electron spectrometry, transmission electron microscopy, and X-ray diffraction on reaction products extracted using the electrochemical dissolution. The value of these combined techniques in elucidating the morphologies of the interfacial reaction products was also demonstrated. The influence that each fabrication process has on the extent of the interfacial reaction was studied. Adequate process parameters to fabricate SiC p /Al alloy composites were proposed based on thermodynamic considerations.

Prediction of Si contents to suppress the interfacial reaction in the SiCp/2014 Al composite

Abstract Equilibrium Si contents required to prevent the interfacial reaction in the SiC p /2014 Al composite were predicted using both theoretical calculations and experimental method. According to the results, equilibrium Si contents increased with increasing temperature; When the composite is exposed at temperatures below the solidus of the matrix, less than 1xa0at.% of Si was found to be sufficient in order to prevent the interfacial reaction. However, Si contents required to prevent the interfacial reaction were observed to increase substantially at temperatures near 600°C such that more than 5xa0at.% of Si was required to prohibit the interfacial reaction even at 620°C. Application of such results for designing the matrix alloy and selecting process parameters for the semi-solid forming were demonstrated.

Effect of deformation histories on texture evolution during equal- and dissimilar-channel angular pressing

Abstract Finite element analyses and full constraint Taylor analyses based on the rate sensitivity model were performed to analyze deformation history and corresponding texture evolution during equal- and dissimilar-channel angular pressing, respectively.

Methodologies to observe and characterize interfacial reaction products in (Al2O3)pAl and SiCppAl composites — Using SEM, XRD, TEM

Improved mechanical properties of metal-matrix composites reinforced with ceramic particles are due to the transfer of shear load at the matrix/reinforcement interface. As a result, composite interfaces play important roles in determining the resultant composite properties. The aim of the present study is twofold: (a) to identify the interfacial reaction products using X-ray diffractometry (XRD) and CBED, and (b) to demonstrate detailed 3-dimensional morphologies of the interfacial reaction products using SEM. Powder extraction procedure employed for XRD and SEM applications is also presented.

Joining characteristics of oxidized SiC particles reinforced Al-Mg matrix composite prepared by reaction infiltration processing

The joining characteristics of oxidized SiC particles with Al–Mg alloy during reaction infiltration processing for fabrication of the composite were studied. From the measurement of weight changes due to the transformation from SiC into SiO2, it became clear that the thickness of SiO2 layer which was formed at the surface of SiC particles increased parabolically with holding time at the given exposing temperatures. The degree of oxidation of the preform made by SiC particles can be controlled by the application of the present oxidation data. The microstructure observed by field emission scanning electron microscopy showed network skeleton via necklike oxidized-joining among the SiC particles and the compressive strength of the perform increased with oxidation temperature. Furthermore, the microstructure of the composite which was fabricated by Al–2 wt% Mg alloy via reaction infiltration processing was examined and the formation of spinel was observed to join the matrix with the particles like a bridge, which is suitable to make the complicate and strong preforms for the near net-shape composites application in electronic packaging.