Solid State Phenomena Vol. 297

Abstract: Friction stir welding is a solid-phase welding process based on the mixing of the pasty material in the stirred zone. The main advantage of this technique is the ability to weld metal alloys which are generally difficult to weld by conventional welding processes. In this paper an analytical model is proposed for the description in 2D the distribution of the material (fluid) flow in the vicinity of the tool pin during friction stir welding process "FSW". For this reason, the analytical solutions are built on the basis of traditional problem of mechanics of the fluids which is used to solve the equation associated with this problem. Furthermore, the aim is to make an analytical study of these aspects for a better understanding of this phenomenon. This method provides a reduction in computational time compared to those required for finite or differential elements methods. Moreover, it highlights on the effects of the different parameters on the material flow during welding.

Abstract: A dissimilar metal joining method based on diffusion bonding was developed to join 304L stainless steel (SS) and Zr alloy (Zy-4). This was done at 820°C and 950°C under argon and dynamic pressure for 45 minutes.The metallurgical structure of the interface and the evolution of its texture during the treatment were studied by evaluating the distribution of the constituent chemical elements and by identifying the crystalline phases formed. Chemical exchanges through the interface are favored by diffusion phenomena. The junction was characterized by: microscopic observations and chemical analyzes (ESEM-EDS, EPMA), X-RD and mechanical tests (HV and Shear test). Treatment at 820°C does not form a bond because the reciprocal solubilities of the chemical elements of SS and Zy-4 are very low. The junction obtained at 950°C has a reaction zone (RZ) formed at the SS/Zy-4 interface, composed of three layers. The first layer (LI = α-(Fe,Cr) on the SS side and the third layer (LIII=Zr₂(Fe, Ni)) on the Zy-4 side are single-phased. The middle layer LII is biphasic (LII= e-Zr(Cr,Fe)₂+Zr₂(Fe, Ni)). The maximum hardness measured in the RZ is ~ 1120 HV. It is due to the formation of the intermetallic compounds of type e-Zr(Cr,Fe)₂ in LII. Examination of fracture facies obtained from the joints reveals that the fracture is localized in the LIII layer and it is fragile in nature of the trans-granular type.

Abstract: The comprehension of the anisotropy impacts on mechanical properties of the rolled steel sheets was investigated using a non-quadratic anisotropic yield function. In this study, experimental and modelling determination of behavior of an industrial rolled sheets for a DIN 1623 St14 steel were carried out. The yield stresses and Lankford r-values in uniaxial were experimentally determined but the balanced biaxial tension stress states and rb were assumed. The parameters of the associated yield equation, derived from the three orthotropic yield functions proposed by Hill48 and Yld2000-2d, were determined. Predictions and the evolution of normalized yield stress and normalized Lankford parameters (plastic strain ratio) obtained by the presented investigative are considered. In order to describe the path of equivalent plastic behavior, the isotropic hardening function is described using the following various empirical standard formulae based on: Hollomon, Ludwick, Swift and Voce model.

Abstract: The optimization of mechanical properties of the welded joints requires a statistical approach such as Taguchi experimental designs associated with experimental techniques and laboratory characterizations. The aim of this work is to propose a method of optimization of the mechanical performances of a TIG dissimilar welding of two grades of steels: a high strength low alloy steel X70 and an austenitic stainless steel 304L. The experimental designs were chosen according to the Taguchi method L9. The metallurgical characterization includes optical microscopy, SEM microscopy, EDX analyses and mechanical tests to establish a relationship between welding parameters, microstructures and mechanical behavior in different zones of a dissimilar weld joint. The results showed that the hardness is more strongly related to microstructural evolution than tensile strength of dissimilar joint. It was found that gas flow is the main significant TIG welding parameter affecting dissimilar weld characteristics.

Abstract: This paper studied the influence of cellulosic flux on the chemical composition, microstructure, formation of inclusions and micro hardness of X42 welded steel. The chemical compositions of the used fluxes are FA: E6010 and FB: E8010-P1, with electrodes has low carbon content. The welding conditions are not constant. The fluxes (FA and FB) have a high content of TiO₂ and SiO₂ and a low Ti and Si content was also detected in the internal (P1) and external (P3) passes. But there was an increase in the Ti content in the fusion zone (P1, P2 and P3) of the different passes gradually, compared to the base metal. The microstructure of the fusion zone (P1, P2 and P3) for each flux is mainly composed of acicular ferrite. The mass concentration variation of Mn is more elevated through the centers of the fusion zone passes (P1, P2 and P3) with the used fluxes. White and black non-metallic inclusions are observed, regardless of used flux. The micro-hardness in fusion zone varies according to the variation of the equivalent carbon in the different electrodes.

Abstract: An artificial neural network (ANN) model has been developed for the analysis and simulation of the correlation between the chemical composition and mechanical properties of high strength low alloy (HSLA) steel X70. The input parameters of the model consist of the base metal chemical composition (C, Si, Mn, the sum of Cr+Cu+Ni+Mo, the sum of Nb+Ti+V, carbon equivalent CEpcm) and the yield strength (YS). The outputs of the ANN model include the ultimate tensile strength (UTS) of the test material. Scatter plots, correlation coefficient (R) and mean relative error (MRE) were used to assess the performance of the developed neural network. Interestingly, the model output is efficient to calculate the mechanical properties of high strength low alloy steels, especially the ultimate tensile strength as a function of chemical composition and yield strength of the used material. The obtained results are in a good agreement with experimental ones, with high correlation coefficient and low mean relative error. The predictions accuracy of the developed model also conforms to the results of mean paired T-test.

Abstract: In this work we investigated the structural, electronic and elastic properties of TlN, TlP, TlAs and TlSb compounds in the zinc-blende phase, the lattice parameter, bulk modulus, band structure, and elastic constants have been calculated by employing the full potential linearized augmented plane wave method based on density functional theory of the exchange-correlation potentials including local density approximation, PBE generalized gradient, and Wu-Cohen generalized gradient are used. Furthermore, the modified Backe-Johnson (mBJ) potential has been utilized for the calculation of the energy gap. The present results are compared with other available theoretical values obtained.

Abstract: This work concerns the numerical modeling of stationary conduction heat transfer in a 3D three-dimensional anisotropic material subjected to an internal heat source, based on the finite element method MEF and using the Galerkin method. The field of study is a cube representing the seven crystalline systems subjected to an internal heat source and convective boundaries. The obtained equation system is solved by the LU method. The automatic mesh is managed for all the domain nodes via the program which we have written in FORTRAN language. This program allowed temperature field calculation and was applied for different crystalline systems: monoclinic, triclinic, orthorhombic, trigonal, cubic that are identified by their thermal conductivity tensors [kij]. The obtained temperature profiles obtained are in accordance with heat transfer theory and clearly illustrate the crystalline structure symmetry; this calculation permits to predict the possible thermal deformations in an anisotropic solid.

Abstract: An analytical of new theoretical model has been developed to study the Capacitance characteristics for an optically controlled Gallium Arsenic Metal Semiconductor Field Effect Transistor MESFET (OPFET) doped uniformly. The model takes the effects of photoconductive and photovoltaic into account that determine the device characteristics in the illuminated condition. It has been presented here for an analysis of extrinsic and intrinsic parameters such as, gate capacitances including both of the gate-source capacitances gate-drain capacitances under dark and illumination condition. The numerical results have also been compared with the reported data experience in the literature and a good agreement is observed.