Thermal stability of ultrasoft Fe–Zr–N films

The thermal stability of nanocrystalline ultrasoft magnetic (Fe98Zr2)1−xNx films with x = 0.10–0.25 was studied using thermal desorption spectrometry, positron beam analysis and high resolution transmission electron microscopy. The results demonstrate that grain growth during the heat treatment is accompanied by an increase of the free volume and nitrogen relocation and desorption. All these phenomena can drastically degrade the ultrasoft magnetic properties. The nitrogen desorption has already started at temperatures around 400 K. Nevertheless, most of the nitrogen leaves the sample at a temperature above 800 K. We found that nitrogen out-diffusion is significantly retarded compared with the prediction of the diffusion in bulk α-Fe. A qualitative model is proposed in which the nitrogen out-diffusion in nanocrystalline material is retarded by trapping at immobile defects, namely Zr atoms, and also by voids at grain boundaries. From a certain temperature, nitrogen migrates from the interior of the nanograins to the nanovoids at the grain boundaries and the out-diffusion to the outer surface is controlled by transport between the voids.

Role of Mastoid Pneumatization in Temporal Bone Fractures

ABSTRACT BACKGROUND AND PURPOSE: The mastoid portion of the temporal bone has multiple functional roles in the organism, including regulation of pressure in the middle ear and protection of the inner ear. We investigated whether mastoid pneumatization plays a role in the protection of vital structures in the temporal bone during direct lateral trauma

Growth and properties of strained VOx thin films with controlled stoichiometry

We have succeeded in growing epitaxial films of rocksalt VOx on MgO(001) substrates. The oxygen content as a function of oxygen flux was determined using 18O2-RBS and the vanadium valence using XAS. The upper and lower stoichiometry limits found are similar to the ones known for bulk material (0.8<x<1.3). From the RHEED oscillation period a large number of vacancies for both vanadium and oxygen were deduced, i.e. ~16% for stoichiometric VO. These numbers are, surprisingly, very similar to those for bulk material and consequently quite strain-insensitive. XAS measurements reveal that the vacancies give rise to strong low symmetry ligand fields to be present. The electrical conductivity of the films is much lower than the conductivity of bulk samples which we attribute to a decrease in the direct overlap between t2g orbitals in the coherently strained layers. The temperature dependence of the conductivity is consistent with a variable range hopping mechanism.Comment: 12 pages, 16 figures included, revised versio

Material variability effects on automotive part production process

The current efforts to reduce the carbon footprint throughout the chain in the automotive industry by increased use of recycled materials poses new challenges for materials production and their use. The increase of steel scrap fraction in the current primary steel making processes, used for producing steel sheet metal for automotive components, possibly affects the material properties variability beyond the limits observed in the materials produced today despite mitigating actions in steel production. In this paper material variability increase was modelled by selecting deterministic values outside the range of the material grade used to design and manufacture an automotive part. The values were selected from an experimental data set representing the cold rolled mild steels material class range. The effects were studied numerically on a reverse engineered model of an existing automotive part production process. It was found that the manufacturing feasibility in this particular case is mainly affected by the weighted average plastic strain ratio and less by the degree of planar anisotropy

Positron annihilation in gaseous nitrided cold-rolled FeNiTi films

Positron beam analysis (PBA) was performed on cold-rolled Fe0.94Ni0.04Ti0.02 foils, which were subjected to different thermal treatments in an atmosphere of a gas mixture of NH3+H-2 (nitriding). The nitriding of the samples in the alpha -region (alphaN) of Lehrer diagram for the Fe-N system produced a large decrease of the central part of the Doppler broadened annihilation gamma -peak (S-parameter) and an increase of the contribution to the wings of the peak (W-parameter). The effect was much more pronounced for the (x-nitrided samples than for samples annealed in vacuum at the same temperature. A reduction of the alphaN-samples by annealing in H-2-atmosphere brings the S-parameter to a higher value. Further nitriding of alphaN-samples in the gamma'-region (alphaN+gamma 'N) of the Lehrer diagram increases S and lowers the W-parameter compared with the alphaN-samples. The changes in S- and W-parameters are interpreted on the basis of the evolution of microstructure of the films during the processing.</p

Accurate sheet metal forming modeling for cost effective automotive part production

Recent implementations of accurate material and tribology models in finite element codes for sheet metal forming process development have the potential to reduce development time and the associated development costs significantly. Adoption of new models requires validated material parameters and assessments of the overall accuracy. The paper presents a study aimed at accuracy estimation by comparing strain measurements and finite element simulation results for a laboratory flat bottom hole expansion test and an industrial automotive component produced at Volvo Cars. The use of the tensile test based Tata Steel Vegter yield locus model results in accurate prediction of dimensions and plastic deformation distribution in sheet metal forming applications. © Published under licence by IOP Publishing Ltd.open access</p