none

In our research, aluminum (1050) was deformed by plane strain compression (PSC) up to 65% reduction. The total deformation conditions include four temperatures (from 150oC to 300oC) and two strain rates (5¡Ñ10-2s-1 and 5¡Ñ10-4s-1). After the deformation, the specimens were examined by TEM for observing the morphology of the microstructures and measuring various parameters, which includes the sizes and aspect ratios of dislocation cells, as well as the distribution of misorientation angles for dislocation walls. At last, the proportions of GNBs and IDBs were tried to be determined.

none

none

There exists considerable debate in the texture community about whether grain interactions are a necessary factor to explain the development of deformation textures in polycrystalline metals. Computer simulations indicate that grain interactions play a significant role, while experimental evidence shows that the material type and starting orientation are more important in the development of texture and microstructure. A balanced review of the literature on face-centered cubic metals shows that the opposing viewpoints have developed due to the lack of any complete experimental study which considers both the intrinsic (material type and starting orientation) and extrinsic (grain interaction) factors. In this study, a novel method was developed to assemble ideally orientated crystalline aggregates in 99.99\% aluminum (Al) or copper (Cu) to experimentally evaluate the effect of grain interactions on room temperature deformation texture. Ideal orientations relevant to face-centered cubic rolling textures, Cube $\{100\}\left<001\right>$, Goss $\{110\}\left<001\right>$, Brass $\{110\}\left<1\bar{1}2\right>$ and Copper $\{112\}\left<11\bar{1}\right>$ were paired in different combinations and deformed by plane strain compression to moderate strain levels of 1.0 to 1.5. Orientation dependent mechanical behavior was distinguishable from that of the neighbor-influenced behavior. In interacting crystals the constraint on the rolling direction shear strains ($\gamma_{_{XY}}, \gamma_{_{XZ}}$) was found to be most critical to show the effect of interactions via the evolution of local microstructure and microtexture. Interacting crystals with increasing deformations were observed to gradually rotate towards the S-component, $\{123\}\langle\bar{6}\bar{3}4\rangle$. Apart from the average lattice reorientations, the interacting crystals also developed strong long-range orientation gradients inside the bulk of the crystal, which were identified as accumulating misorientations across the deformation boundaries. Based on a statistical procedure using quaternions, the orientation and interaction related heterogeneous deformations were characterized by three principal component vectors and their respective eigenvalues for both the orientation and misorientation distributions. For the case of a medium stacking fault energy metal like Cu, the texture and microstructure development depends wholly on the starting orientations. Microstructural instabilities in Cu are explained through a local slip clustering process, and the possible role of grain interactions on such instabilities is proposed. In contrast, the texture and microstructure development in a high stacking fault energy metal like Al is found to be dependent on the grain interactions. In general, orientation, grain interaction and material type were found to be key factors in the development of rolling textures in face-centered cubic metals and alloys. Moreso, in the texture development not any single parameter can be held responsible, rather, the interdependency of each of the three parameters must be considered. In this frame-work polycrystalline grains can be classified into four types according to their stability and susceptibility during deformation. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-09-25 23:59:11.809

Le forgeage multi-matériaux est un procédé permettant la mise en forme et l’assemblage simultanés de matériaux différents. Ce procédé permet d’obtenir des pièces multi-matériaux avec le « bon matériau placé au bon endroit ». L’objectif des travaux de thèse est de définir les conditions nécessaires à l’établissement de la liaison métallurgique par forgeage à l’interface d’un couple d’aciers. Dans un premier temps, l’état de l’art a servi à l’identification les phénomènes physiques accompagnant le forgeage multi-matériaux et les paramètres clés pilotant l’établissement de la liaison métallurgique. Le principe de base de l’établissement d’une liaison passe par la fragmentation des oxydes en surface des matériaux et par l’application d’une pression de contact favorisant le contact entre les matériaux nus et la diffusion. Les deux paramètres clés identifiés sont donc la pression normale de contact et l’expansion de surface. Le protocole de caractérisation du co-forgeage mis en place comporte trois essais « simples » permettant de solliciter les interfaces avec des pressions et des expansions différentes. Ces dernières, estimées par simulation numérique de l’essai, sont mises en relation avec la qualité des liaisons obtenues évaluée, quant à elle, au travers d’observations métallographiques. Les premières simulations permettent de dimensionner les campagnes expérimentales. Celles-ci sont ensuite conduites sur les moyens de mise en forme de la plateforme VULCAIN. Les efforts de mise en forme et la géométrie globale des pièces et la répartition de matière servent de base à l’identification des paramètres de la simulation. La simulation ainsi obtenue et les observations métallographiques aux interfaces sont ensuite mises en lien. Cette démarche a permis de confirmer l’importance du rôle joué par la pression de contact et l’expansion de surface sur l’établissement d’une liaison au cours de la mise en forme du multi-matériaux. La répartition et la forme des particules d’oxydes semblent liées au chemin thermomécanique subi par l’interface. / The multi-material forging is a forming process allowing, simultaneously, the welding and shaping of multi-material parts with the right material at the right place. The purpose of the presented work is to identify the necessary conditions to obtain a metallurgical bond during forming between two different grades of steel. First, the state of the art allowed the identification of the physical phenomena occurring during multi-material forging and the determination of the key parameters of the bonding which are the contact pressure and the surface expansion at the both sides of the interface. The mechanisms to establish metallurgical bond by forging are based on the breaking and the dispersion of the oxide layer at the interface then the extrusion of the soft material through the voids generated between the oxide fragments. Second, the characterization methodology of this work is presented. It consists of three “simple” forming tests leading to different interface conditions (contact pressure and surface expansion). The first simulations allow the design of the experimental plan for each test. The comparison between simulations and experiments allows the identification of physical parameters of the simulation. Then, the contact pressure and the surface expansion of the identified simulations are used to analyze the metallographic structure and the bonding at the interface.The developed work confirms the major effect of the contact pressure and the surface expansion on the establishment of a metallurgical bond during multi-material forming. The size and the shape of the oxide particles seem to depend on the thermomechanical path at the interface.