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Oxide Dispersed Strengthened (ODS) ferritic stainless steels present well-known fine grains microstructures where dislocation movement is hindered by a dense precipitation of nano-oxides particles. Previous research, on the thermomechanical behavior at high temperature and strain rates, was focused on torsion tests (Karch in J Nucl Mater 459:53-61, 2014). Considering texture evolution and grain shape as indicators of the intragranular dislocation glide activity, it was shown that, for high temperature and strain rate, intragranular deformation was in competition with intergranular accommodation. The latter phenomenon was related to early damaging at grain boundaries. The occurrence of a transition phenomenon from an intragranular to an intergranular deformation mechanism, with increasing temperature, was recently confirmed by neutron diffraction spectroscopy (Stoica in Nature Commun 5:5178, 2014). In the present paper, hot extrusion (HE) tests are performed, avoiding damage due to the high stress triaxiality, and allowing further investigation of intragranular and intergranular plasticity at large strains. Three ferritic steels exhibiting various precipitation size and density were hot extruded. Microstructure evolution at different stages of deformation is investigated using the Electron Back-Scattered Diffraction (EBSD) technique. After extrusion at 1373 K (1100 °C), the microstructure of ODS steels consists of a mixture of small round shape grains and larger elongated grains containing low-angle grain boundaries. Texture measurements show the appearance of the α-fiber (<110>//extrusion direction) and an increase in its intensity during the extrusion process in the larger grains. The fragmentation of the large elongated grains by Continuous Dynamic Recrystallization (CDRX) partially occurs in ODS materials depending on precipitation reinforcement. For smaller grains, plastic deformation has no effect on crystallographic orientation and grain shape, indicating a grain boundary accommodation phenomenon as the major deformation mechanism. Precipitation density not only impacts the intragranular dislocation glide activity, but also reduces CDRX kinetics in coarse grains. [ABSTRACT FROM AUTHOR]

This paper gives an overview of “Grain boundary engineering (GBE) for advanced materials by magnetic field application” based on recent experimental work performed on different kinds of structural and functional materials. It is shown that magnetic field application has a great potential and unique advantage as “non-contact processing” for microstructure control, irreplaceable by any other existing processing methods. The control of grain growth and texture by magnetic fields has been found to be generally applicable to many metallic materials, irrespective of whether they are ferromagnetic or not. Grain growth which is controlled by grain boundary migration was found to be strongly affected by magnetic field application. Recent attempts at the grain boundary engineering by magnetic field application through phase transformation have revealed that magnetic phase transformation can provide us a new approach to grain boundary engineering for iron alloys and steels, as well as a new nanocrystalline material produced by magnetic crystallization from the amorphous state. The possibility of engineering applications of enhanced densification using magnetic sintering and magnetic rejuvenation has been discussed for iron powder compacts and deformation-damaged iron alloys, respectively. [ABSTRACT FROM AUTHOR]

This paper reports an experimental investigation on the effect of multiple twinning on the interface population in two low stacking-fault alloys. This is an important topic for grain boundary engineering because annealing twinning is the indirect cause of improved intergranular corrosion resistance in this class of materials. Proportions of S 3n (n= 1-5) boundaries were analysed in both a brass specimen and a superalloy specimen where the boundaries had been processed so as to be very mobile and less mobile respectively. When S 3 twin boundaries (as distinct from S 3 grain boundaries) are discounted, the S 3n distribution for both specimens had a peak at S 9, because S 3 + S 9 ? S 3 occurs more frequently than S 3+S 9 ? S 27. The distributions and reactions between various S 3n values are described and discussed in detail. A novel trace analysis procedure is used to extract information from S 3 boundaries to decide whether or not they are annealing twins, and so provide a convenient means to assess proportions of twin and non-twin S 3s. The data show unambiguously that a significant proportion of S 3s are not on 111, and these boundaries have on average higher angular deviations from the exact S 3 reference misorientation than do other S 3s. A population of S 3s which were vicinal to annealing twins were also recorded. These data support the contention that profuse annealing twinning produces concurrently many not-twin S 3s, which are pivotal in grain boundary engineering. [ABSTRACT FROM AUTHOR]