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Modelling the flow behaviour, recrystallisation and crystallographic texture in hot deformed Fe-30wt%Ni Austenite
Abstract: The present work describes a hybrid modelling approach developed for predicting the flow behaviour, recrystallisation characteristics and crystallographic texture evolution in a Fe-30wt%Ni austenitic model alloy subjected to hot plane strain compression. A series of compression tests were performed at temperatures between 850 and 1050ºC and strain rates between 0.1 and 10 s-1. The evolution of grain structure, crystallographic texture and dislocation substructure was characterised in detail for a deformation temperature of 950ºC and strain rates of 0.1 and 10 s-1, using electron backscatter diffraction and transmission electron microscopy. The hybrid modelling method utilises a combination of empirical, physically-based and neuro-fuzzy models. The flow stress is described as a function of the applied variables of strain rate and temperature using an empirical model. The recrystallisation behaviour is predicted from the measured microstructural state variables of internal dislocation density, subgrain size and misorientation between subgrains using a physically-based model. The texture evolution is modelled using artificial neural networks
Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel
In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of
post-irradiated austenitic stainless steel in Light Water Reactor (LWR)
environment, reliable predictions of intergranular stresses are required.
Finite elements simulations have been performed on realistic polycrystalline
aggregate with a recently proposed physically-based crystal plasticity
constitutive equations validated for neutron-irradiated austenitic stainless
steel. Intergranular normal stress probability density functions are found with
respect to plastic strain and irradiation level, for uniaxial loading
conditions. In addition, plastic slip activity jumps at grain boundaries are
also presented. Intergranular normal stress distributions describe, from a
statistical point of view, the potential increase of intergranular stress with
respect to the macroscopic stress due to grain-grain interactions. The
distributions are shown to be well described by a master curve once rescaled by
the macroscopic stress, in the range of irradiation level and strain considered
in this study. The upper tail of this master curve is shown to be insensitive
to free surface effect, which is relevant for IGSC
Semi phenomenological modelling of the behavior of TRIP steels
The authors are grateful to ArcelorMittal R&D for supporting this research.A new semi-phenomenological model is developed based on a mean-field description of the TRIP behavior for the simulation of multiaxial loads. This model intends to reduce the number of internal variables of crystalline models that cannot be used for the moment in metal forming simulations. Starting from local and crystallographic approaches, the mean-field approach is obtained at the phase level with the concept of Mean Instantaneous Transformation Strain (MITS) accompanying martensitic transformation. Within the framework of the thermodynamics of irreversible processes, driving forces, martensitic volume fraction evolution and an expression of the TRIP effect are determined for this new model. A classical self-consistent scheme is used to model the behavior of multiphased TRIP steels. The model is tested for cooling at constant loads and for multiaxial loadings at constant temperatures. The predictions reproduce the increase in ductility, the dynamic softening effect and the multiaxial behavior of a multiphased TRIP stee
Mechanisms of electron scattering in uniaxially deformed - single crystals
Temperature dependencies for concentration and the Hall mobility of electrons
for the - and \linebreak
- single crystals
uniaxially deformed along the crystallographic directions [100] and [111] are
obtained on the basis of piezo-Hall effect measurements. A deformation-induced
increase of the Hall mobility of electrons for - single crystals at the uniaxial pressure along the
crystallographic direction [100] has been revealed. A comparison of the
obtained experimental results with the corresponding theoretical calculations
of temperature dependencies of the Hall mobility showed that the obtained
effect occurs at the expense of the reduction probability of electron
scattering on the fluctuational potential. Its amplitude depends on the
tempe\-rature and on the value of the uniaxial pressure. It has also been shown
that an increase of the Hall mobility for the - single crystals uniaxially deformed along the
crystallographic direction [111] with an increasing temperature turns out to be
insignificant and is observed only for the uniaxial pressures GPa. A
decrease of the Hall mobility of electrons at the expense of the deformational
redistribution of electrons among the valleys of the germanium conduction band
with different mobility should be taken into account in the present case. The
Hall mobility magnitude for the uniaxially deformed - single crystals is determined only by the mechanisms
of phonon scattering and we have not observed the effect of the growth of the
Hall mobility with an increase of temperature or the magnitude of uniaxial
pressure.Comment: 10 pages, 7 figure
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