arXiv subjects

T. Truglas

Publications and source records attributed to T. Truglas.

2 recordsLinked to original sources

arXiv2021

Nanoscale Investigation of Microcracks and Grain Boundary Wetting in Press Hardened Galvanized 20MnB8 Steel

Grain boundary wetting as a preliminary stage for zinc induced grain boundary weakening and embrittlement in a Zn coated press hardened 20MnB8 steel was analyzed by means of electron backscatter diffraction, Auger electron spectroscopy, energy dispersive X-ray analysis, atom probe tomography and transmission electron microscopy on the nanometer scale. Microcracks at prior austenite grain boundaries were observed and structures that developed after microcrack formation were identified. Zn/Fe intermetallic phases with grain sizes smaller than 100 nm in diameter are present at the crack surfaces and at the wedge-shaped crack tips. In order to get a complete picture, including the microstructure before cracking, an undeformed, electrolytically coated reference sample which underwent the same heat treatment as the press hardened material was investigated. Here, Zn, in the order of one atomic layer or less, could be found along prior austenite grain boundaries several micrometers away from the actual Zn/Fe phases in the coating. Such a grain boundary weakening by Zn wetting of prior austenitic grain boundaries during austenitization and/or hot forming is a necessary condition for microcrack formation.

cond-mat.mtrl-sci↗

arXiv2020

Out-of-Plane Magnetic Anisotropy in Ordered Ensembles of Fe$_y$N Nanocrystals Embedded in GaN

Phase-separated semiconductors containing magnetic nanostructures are relevant systems for the realization of high-density recording media. Here, the controlled strain engineering of Ga$δ$FeN layers with Fe$_y$N embedded nanocrystals (NCs) \textit{via} Al$_x$Ga$_{1-x}$N buffers with different Al concentration $0<x_\mathrm{Al}<41$\% is presented. Through the addition of Al to the buffer, the formation of predominantly prolate-shaped $\varepsilon$-Fe$_3$N NCs takes place. Already at an Al concentration $x_\mathrm{Al}$\,$\approx$\,5\% the structural properties---phase, shape, orientation---as well as the spatial distribution of the embedded NCs are modified in comparison to those grown on a GaN buffer. Although the magnetic easy axis of the cubic $γ$'-Ga$_y$Fe$_{4-y}$N nanocrystals in the layer on the $x_\mathrm{Al} = 0\%$ buffer lies in-plane, the easy axis of the $\varepsilon$-Fe$_3$N NCs in all samples with Al$_x$Ga$_{1-x}$N buffers coincides with the $[0001]$ growth direction, leading to a sizeable out-of-plane magnetic anisotropy and opening wide perspectives for perpendicular recording based on nitride-based magnetic nanocrystals.

cond-mat.mtrl-sci↗