This paper concentrates on the superplastic response of fine-grained and coarse-grained Al-Mg alloys under uniaxial tension. To identify the main characteristics of superplastic deformation and to determine the optimum deformation parameters, the microstructure and dislocation substructure of the alloys are analyzed as a function of strain, strain rate and temperature using electron backscatter diffraction and transmission electron microscopy (TEM). Under optimum deformation conditions of temperature and strain rate, these Al-Mg alloys have an elongation to failure in excess of 300%. Dynamic recrystallization is dominant at strain rates in excess of 10 À1 s À1 and results in a strong coarsening of the microstructure and premature failure. Dynamic recovery prevails at a strain rate of around 10 À2 s À1 , leading to great enhancement of the plasticity of the coarse-grained materials. TEM observations show that subgrain formation proceeds slowly. During initial straining, subgrains are formed primarily along the original grain boundaries. This results in a ''core and mantle'' microstructure, with dynamic recovery mainly taking place in the mantle region. A uniform substructure is established at a strain of the order of 1.

Soft magnetic films with high saturation magnetization and controllable uniaxial anisotropy are required for future high frequency applications. However, the origin and magnitude of the induced magnetic anisotropy are still a contradictory issue. In this paper we show the influence of the structure and composition of sputtered Fe-Zr-N films upon the coercivity and the induced uniaxial magnetic anisotropy. We have found that the increase of the nitrogen content of the sputtered films leads to a reduction of the grain size and a strong increase of the uniaxial anisotropy. The value of 20 Oe for the anisotropy field combined with a saturation magnetization of 20 kG found in a film with average grain size as low as 10 nm gives a ferromagnetic resonance frequency of 1.8 GHz and a roll-off frequency of 1.2 GHz. Such a film is a promising candidate to be used as an ultra-high frequency inductor.Introduction Soft magnetic materials with high saturation magnetization and controllable uniaxial anisotropy are required for future high frequency inductors as well as for high-density recording heads. Such materials must have a well-controlled domain pattern with the magnetization, in the absence of an external magnetic field, oriented in most of the domains parallel to the direction of the anisotropy axis. The hysteresis loop will be a rectangle in the easy direction (domain wall movement) and a straight line in the hard direction (spin rotation). When an external ac field is applied perpendicular to the easy axis the magnetization oscillates with the field. The permeability in this case is given by the ratio between the saturation magnetization (M S ) and the anisotropy field (H K ). This value can be maintained up to the ferromagnetic resonance (FMR) frequency [1] which is given by f r ¼ 2pg(4pM S H K ) 1/2 , were g is the gyromagnetic constant (2pg ¼ 2.8 MHz/Oe).The magnetic domain pattern can be controlled by reduction of the grain size below the ferromagnetic exchange length (the contribution of the magnetocrystalline anisotropy is averaged out) and by introducing an uniaxial anisotropy. Promising materials for this purpose were found to be FeMN thin films, with the typical M being Ta [2], Cr [3], Zr [4], etc. In the past decade large efforts were spent in optimising the microstructure and composition of these materials in order to get optimal magnetic properties. However, the information about the origin and magnitude of induced uniaxial anisotropy is often contradictory. In this paper we show the influence of the nitrogen content on grain size, coercivity and induced anisotropy in 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.

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Using various experimental techniques, the formation and evolution of precipitates, the dilation of the matrix, and the nitrogen uptake and release were investigated in cold-rolled Fe 94 Ni 4 Ti 2 and Fe 93 Ni 4 Cr 3 materials subjected to nitriding in a gaseous mixture of NH 3 ϩ H 2 and to reduction in an H 2 atmosphere at low (300 ЊC) to moderate (600 ЊC) temperatures. Transmission electron microscopy (TEM) revealed that in both alloys the precipitates are thin platelets. In the Ti-containing alloy, the precipitates were also small in the lateral dimensions. The difference in size, aspect ratio of the precipitates, and misfit and coherency on the interface consistently explain the substantial differences in dilation of the matrix and nitrogen uptake for the Ti-and Cr-containing alloys under examination. The results provide evidence for the formation of mixed Fe-Ti-N precipitates (Guinier-Preston (GP) zones) in the early stages of nitriding.