Mechanical properties, microstructure and crystallographic texture of magnesium AZ91-D alloy welded by Friction Stir Welding (FSW)

The objective of the study was to characterize the properties of a magnesium alloy welded by friction stir welding (FSW). The results led to a better understanding of the relationship between this process and the microstructure and anisotropic properties of alloy materials. Welding principally leads to a large reduction in grain size in welded zones due to the phenomenon of dynamic recrystallization. The most remarkable observation was that crystallographic textures appeared from a base metal without texture in two zones: the thermo-mechanically affected and stir welded zones. The latter zone has the peculiarity of possessing a marked texture with two components on the basal plane and the pyramidal plane. These characteristics disappeared in the TMAZ, which had only one component following the basal plane. These modifications have been explained by the nature of the plastic deformation in these zones, which occurs at a moderate temperature in the TMAZ and high temperature in the SWZ

Study of the development of the cube texture in Fe-50%Ni during recrystallization and normal grain growth

The development of the cube texture has been investigated in a Fe-50%Ni alloy undergoing recrystallization and normal grain growth by means of orientation imaging microscopy (OIMTM) and bulk texture measurements (X-ray diffraction). It is shown that both the oriented nucleation and the oriented growth mechanisms are responsible for the strengthening of the cube texture in the early stages of recrystallization in this alloy. The increase in the cube texture in the intermediate stages of recrystallization is mainly related to the high differentials in stored energy associated with cube grains. These experimental results are corroborated by way of a Monte-Carlo simulation of recrystallization based on data derived by OIM of the investigated alloy at its earliest recrystallization stages. The primary mechanism responsible for the development of the cube texture during grain growth relies on the preferential migration of the high-angle grain boundaries linked to cube grains which results from the advantage in number and size shown by cube grains when recrystallization is complete

Comparison of several methods for the reproduction of the orientation distribution function from pole figures in medium to strong textured materials

International audienceA quantitative comparison of the errors introduced by several methods for the reproduction of the crystallographic orientation distribution function from poles figures is presented. The harmonic, ADC, WIMV and component methods have been employed in the characterization of the deformation and recrystallization textures of a Fe-50% Ni alloy in order to investigate the accuracy associated with each one of these methods. To carry out this study, experimental and synthetic pole figures have been used as input data. The strong and weak points of each method are examined showing that the iterative discrete methods (ADC and WIMV) are better suited for the reproduction of the texture function in the present case. In comparing these two discrete methods, it is evidenced that the ADC method reproduces more accurately both the experimental and synthetic texture functions over the entire range of texture sharpness considered

Markov Chain Models for the Stochastic Modeling of Pitting Corrosion

The stochastic nature of pitting corrosion of metallic structures has been widely recognized. It is assumed that this kind of deterioration retains no memory of the past, so only the current state of the damage influences its future development. This characteristic allows pitting corrosion to be categorized as a Markov process. In this paper, two different models of pitting corrosion, developed using Markov chains, are presented. Firstly, a continuous-time, nonhomogeneous linear growth (pure birth) Markov process is used to model external pitting corrosion in underground pipelines. A closed-form solution of the system of Kolmogorov's forward equations is used to describe the transition probability function in a discrete pit depth space. The transition probability function is identified by correlating the stochastic pit depth mean with the empirical deterministic mean. In the second model, the distribution of maximum pit depths in a pitting experiment is successfully modeled after the combination of two stochastic processes: pit initiation and pit growth. Pit generation is modeled as a nonhomogeneous Poisson process, in which induction time is simulated as the realization of a Weibull process. Pit growth is simulated using a nonhomogeneous Markov process. An analytical solution of Kolmogorov's system of equations is also found for the transition probabilities from the first Markov state. Extreme value statistics is employed to find the distribution of maximum pit depths

Monte Carlo modeling of low carbon steel recrystallization: Role of thermo-nnechanical treatment and chemical composition.

The recrystallization process of two low-carbon ferritic steels with low fraction of alloying elements are modelled. The difference in chemical composition and initial thermomechanical treatment between these two steels can be the cause of the difference in the stored energy distribution after 40% deformation by cold rolling or plane compression simulated by Finite Element Modelling (FEM). In both cases the deformation texture is characterized by the presence of a gamma-fibre with a reinforcement for the {111} component. The microstructure simulated by FEM is used as initial structure for Monte-Carlo simulations of recrystallization. In these simulations, the variation in chemical composition and initial thermo-mechanical treatment is introduced by the difference in stored energy distribution while recovery, nucleation and grain growth are simulated assuming that grain boundary properties mainly depend on misorientation Modelling. results are in agreement with experimental observations: that is the presence of a gamma-recrystallization fibre which corresponds to the initial deformed state and the development of {111} component which is not sharp in the deformation microstructure