20 research outputs found
Evolution of microstructure, texture and grain boundary character distribution of potassium doped tungsten fibers annealed at variable temperatures
The effect of the annealing temperature on the microstructure and grain boundary character distribution of potassium doped tungsten fibers made of drawn wire was investigated by Electron Backscatter Diffraction. Samples, with a diameter of 148.7 μm, in the as-received condition and annealed at 1300, 1600, 1900, 2100 and 2300 °C were analyzed at the center of the transversal sections. Up to 1900 °C, a uniform microstructural coarsening and primary recrystallization followed by normal grain growth was observed. Between 1900 and 2100 °C abnormal grain growth took place. The strong texture (<110> parallel to the drawing axis) remained present in all conditions. With increasing the annealing temperature, the low angle grain boundary fraction increased at the expense of high angle grain boundaries while the amount of coincidence site lattice boundaries reached its maximum at 1600 °C. At this temperature, the most resistant configuration of triple junctions against intergranular crack propagation was obtained
Microstructural characterization and mechanical behavior during recrystallization annealing of Nb-stabilized type ASTM 430 and Nb-Ti-stabilized ASTM 439 ferritic stainless steels
Chemical and structural characterization of the native oxide scale on a Mg-based alloy
In this study, the structure and composition of the native oxide forming on
the basal plane (0001) of Mg-2Al-0.1Ca is investigated by a correlative
approach, combining scanning transmission electron microscopy (STEM) and atom
probe tomography (APT). Atom probe specimens were prepared conventionally in a
Ga focused ion beam (FIB) as well as a Xe plasma FIB in a cryogenic setup and
subsequently cleaned in the atom probe to remove surface contamination before
oxidation. While thermal energy input from the laser and longer atmospheric
exposure time increased the measured hydrogen content in the specimen's apex
region, cryo preparation revealed, that the hydrogen uptake in magnesium is
independent of the employment of conventional or cryogenic FIB preparation. TEM
measurements demonstrated the growth of a (111) MgO oxide layer with 3-4 nm
thickness on the basal (0001) plane of the Mg atom probe specimen. APT data
further revealed the formation of an aluminum-rich region between bulk Mg and
the native oxide. The aluminum enrichment of up to ~20 at.% at the interface is
consistent with an inward growth of the oxide scale