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Phase development and changes in crystalline composition of LTCC material during the sintering process were investigated using in-situ X-ray diffraction (XRD) measurements. CeramTape GC was chosen as the chemically simplest model system composed of alumina particles and glass for the investigations. The chemical characterization and microstructural analyses of the tapes sintered with some representative firing profiles were performed by techniques such as (scanning) transmission electron microscope, energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and XRD. Moreover, the porosification behavior of LTCC substrates fired at different peak temperatures was studied. These investigations are important for the subsequent wet chemical etching, representing an approach which allows to reduce locally the permittivity of LTCC tapes. Treatment with a KOH solution shows non-selective etching behavior for all substrates. In addition, highly porous silica structures corresponding to Ca and Al depletion from the anorthite phase were observed in all samples after etching treatment. [ABSTRACT FROM AUTHOR]

Measuring the dimensions and number density of nanoparticles dispersed in a solid matrix is usually accomplished via transmission electron microscopy (TEM) which suffers from high cost, low throughput, and small analytical volume. In comparison, scanning backscattered electron microscopy is inexpensive, requires little sample preparation, and allows for the analysis of large sample areas. However, the information depth is usually not known precisely and depends on several factors such as the composition of the nanoparticles and the matrix as well as the size of the nanoparticles, hindering the reconstruction of the actual size distribution and three-dimensional number density. Here we present a method to estimate the information depth for spherical nanoparticles of different sizes in order to accurately determine size distribution and number density. The approach is based on Monte Carlo simulation of electron trajectories in the material and analysis of the obtained backscattered electron signal-to-noise-ratio. Our experimental results are compared to those obtained via TEM and good agreement is demonstrated; this shows that TEM can be replaced by scanning electron microscopy for studying nanocomposites in many cases. [ABSTRACT FROM AUTHOR]

Proper design of the heat treatments of metallic materials is crucial for creating a suitable microstructure resulting in the desired properties. In this paper, we present a multi-component simulation procedure for the quantitative prediction of yield strength, fracture strain, and fracture toughness of precipitation-hardened alloys, with special emphasis on Al–Mg–Si alloys. The procedure combines thermokinetic and micromechanical models, taking the microstructural information in terms of different populations of various second-phase particles into account. The predictions are compared to the results of experiments performed on AA6082 samples subjected to different artificial aging times, and good quantitative agreement is demonstrated. [ABSTRACT FROM AUTHOR]

In the automotive industry Al-Mg-Si alloys are often chosen for high strength extruded profiles. However, the production of such profiles can be challenging for high alloy contents. Among several processing steps, the homogenization heat treatment before extrusion is readily accessible to modifications to improve high temperature formability. In this work, the influence of five different homogenization variants on the flow stress of AA6082 at elevated temperatures was assessed by compression testing in a deformation dilatometer at 450 °C, 480 °C, and 510 °C. The observed differences in flow stress were interpreted with regards to the microstructure. Samples from billets homogenized at higher soak temperatures exhibited lower hot flow stresses in subsequent dilatometer testing, indicating better processability. Since the decrease in flow stress is approximately constant at all test temperatures, it is suggested that it is due to a lower number density of relatively temperature-stable α-Al(Mn,Fe)Si dispersoids formed during homogenization at higher temperatures; these dispersoids are stable at all three test temperatures. In contrast, the influence of a cooling rate variation was relatively minor and diminishes at higher test temperatures since Mg-Si precipitates – whose size and number density is affected by changes of the cooling rate – are less stable at the higher test temperatures. [ABSTRACT FROM AUTHOR]

Characterization of Mg-Si precipitates is crucial for optimizing the homogenization heat treatment of Al-Mg-Si alloys. Although sample preparation is key for high quality scanning electron microscopy imaging, most common methods lead to dealloying of Mg-Si precipitates. In this article we systematically evaluate different sample preparation methods: mechanical polishing, etching with various reagents, and electropolishing using different electrolytes. We demonstrate that the use of a nitric acid and methanol electrolyte for electropolishing a homogenized Al-Mg-Si alloy prevents the dissolution of Mg-Si precipitates, resulting in micrographs of higher quality. This preparation method is investigated in depth and the obtained scanning electron microscopy images are compared with transmission electron micrographs: the shape and size of Mg-Si precipitates appear very similar in either method. The scanning electron micrographs allow proper identification and measurement of the Mg-Si phases including needles with lengths of roughly 200 nm. These needles are β″ precipitates as confirmed by high resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]