Volume 47, Issue 9

The three dimensional architecture of an AlSi10Cu5NiFe piston alloy in as-cast condition is characterized qualitatively and quantitatively by means of synchrotron tomography and light optical tomography. The same sample is used to correlate and combine the results obtained using both techniques. Synchrotron tomography reveals the long-range interconnectivity, volume fraction and shape of different aluminides present in the studied alloy. The morphology of individual aluminides and their contiguity between each other as well as with the eutectic Si is studied by light optical tomography. The eutectic Si and the Fe-aluminides show a considerable fraction of regions with platelet-like morphologies while the Cu-aluminides and Ni-aluminides show a large fraction of region with convex saddle and convex cylindrical morphologies. The aluminides and the eutectic Si form ≈ 18 vol. % three dimensional hybrid network with a long-range contiguity and interconnectivity located in the interdendritic space.

In the present work, a foundry AlSi8Mg5 alloy is investigated by FIB-Tomography in the as-cast condition and after semi-solid heat treatment. The different microstrutural features are characterized quantitatively using morphological shape factors. The 3D-shape of Mg 2 Si Chinese script as well as Si and impurity Fe containing phases are revealed in high detail. A comparative study with respect to 2D structures is presented as well.

Microstructural evolution during aging treatment in a high tensile precipitation hardening stainless steel (X4CrNiSiTi14-7) has been investigated. Matrix consists of martensitic structure and the combined addition of Si and Ti causes an intermetallic phase type Ni16Ti6Si7 that precipitates with-in grains and enhance precipitation strengthening. This material shows a good combination of high strength and ductility. Light-Optical microscopy, electron back scattered diffraction, transmission electron microscopy and X-ray diffraction analysis have been used to study the microstructural evolution during aging. It has been found that precipitations of various kinds are taking place during aging treatments including nm-scaled G-phase and various carbides. Higher aging temperatures lead to reverse transformation of martensite to austenite.

An as-cast AZ31 magnesium alloy was investigated using light microscopy (LOM) and electron backscatter diffraction (EBSD) methods to quantify and describe the deformation mechanisms activated at high temperatures. Compression tests were carried out by means of a Gleeble®1500 device in the range of 320–500°C and 0.03–10 s-1 of strain rate. Deformed samples were simulated by finite elements method to correlate the microstructure with the local deformation parameters. EBSD measurements were used to distinguish and quantify the new recrystallized grains and to characterize the misorientation distribution. These results helped to determine the grain size distribution with the temperature and the strain rate by LOM pictures. Dynamic recrystallization is denoted by necklace microstructure, and twinning promotes the recrystallization nucleation. At high temperature and slow strain rate recovery takes place followed by continuous dynamic recrystallization.