Recrystallization in Metals and Alloys

When a rod is drawn into wire, a bar is forged, or a sheet is rolled, the grains acquire a preferred orientation or deformation texture. When any of these are subsequently heated to a temperature high enough to create a new population of grains, this population also possesses a texture, usually though not always different from the deformation texture. The process of creation of a population of new grains is called recrystallization (since there is no change of phase, this usage differs from geologists' common usage), the treatment is called annealing and the texture is termed an annealing texture. Recrystallization (Rex) takes place through nucleation and growth. Nucleation during Rex can be defined as the formation of strain-free crystals, in a high energy matrix, that are able to grow under energy release by a movement of high-angle grain boundaries. The nucleus is in a thermodynamic equilibrium between energy released by the growth of the nucleus (given by the energy difference between deformed and recrystallized volume) and energy consumed by the increase in high angle grain boundary area. This means that a critical nucleus size or a critical grain boundary curvature exists, from which the newly formed crystal grows under energy release. This definition is so broad and obscure that crystallization of amorphous materials is called Rex by some people, and Rex can be confused with the abnormal grain growth when grains with minor texture components can grow at the expense of neighboring grains with main texture components because the minor-component grains can be taken as nuclei. In this book, a theory which can determine whether grains survived during deformation act as nuclei and which orientation the deformed matrix is destined to assume after Rex is presented. A lot of Rex textures will be explained by the theory. Recrystallization in metals and metal alloys can proceed discontinuously (creation and motion of recrystallization fronts) or continuously (in situ). Recrystallization in situ is often observed during annealing after very high degrees of deformation or small deformations, in materials with a high content of the second phase particles. Recrystallization mechanism in two-phase alloys is in principle not different from the recrystallization mechanism in single-phase alloys. However, the presence of the second phase particles affects significantly the process kinetics. Rex occurs by nucleation and growth. Therefore, the evolution of the Rex texture must be controlled by nucleation and growth. In the oriented nucleation theory (ON), the preferred activation of a special nucleus determines the final Rex texture. In the oriented growth theory (OG), the only grains having a special relationship to the deformed matrix can preferably grow. Recent computer simulation studies tend to advocate ON theory. This comes from the presumption that the growth of nuclei is predominated by a difference in energy between the nucleus and the matrix, or the driving force. In addition to this, the weakness of the conventional OG theory is in much reliance on the grain boundary mobility. This book is intended to determine the recrystallization mechanism and the sites of recrystallization nucleation in Metals and Alloys. When a rod is drawn into wire, a bar is forged, or a sheet is rolled, the grains acquire a preferred orientation or deformation texture. When any of these are subsequently heated to a temperature high enough to create a new population of grains, this population also possesses a texture, usually though not always different from the deformation texture. The process of creation of a population of new grains is called recrystallization (since there is no change of phase, this usage differs from geologists' common usage), the treatment is called annealing and the texture is termed an annealing texture. Recrystallization (Rex) takes place through nucleation and growth. Nucleation during Rex can be defined as the formation of strain-free crystals, in a high energy matrix, that are able to grow under energy release by a movement of high-angle grain boundaries. The nucleus is in a thermodynamic equilibrium between energy released by the growth of the nucleus (given by the energy difference between deformed and recrystallized volume) and energy consumed by the increase in high angle grain boundary area. This means that a critical nucleus size or a critical grain boundary curvature exists, from which the newly formed crystal grows under energy release. This definition is so broad and obscure that crystallization of amorphous materials is called Rex by some people, and Rex can be confused with the abnormal grain growth when grains with minor texture components can grow at the expense of neighboring grains with main texture components because the minor-component grains can be taken as nuclei. In this book, a theory which can determine whether grains survived during deformation act as nuclei and which orientation the deformed matrix is destined to assume after Rex is presented. A lot of Rex textures will be explained by the theory. Recrystallization in metals and metal alloys can proceed discontinuously (creation and motion of recrystallization fronts) or continuously (in situ). Recrystallization in situ is often observed during annealing after very high degrees of deformation or small deformations, in materials with a high content of the second phase particles. Recrystallization mechanism in two-phase alloys is in principle not different from the recrystallization mechanism in single-phase alloys. However, the presence of the second phase particles affects significantly the process kinetics. Rex occurs by nucleation and growth. Therefore, the evolution of the Rex texture must be controlled by nucleation and growth. In the oriented nucleation theory (ON), the preferred activation of a special nucleus determines the final Rex texture. In the oriented growth theory (OG), the only grains having a special relationship to the deformed matrix can preferably grow. Recent computer simulation studies tend to advocate ON theory. This comes from the presumption that the growth of nuclei is predominated by a difference in energy between the nucleus and the matrix, or the driving force. In addition to this, the weakness of the conventional OG theory is in much reliance on the grain boundary mobility. This book is intended to determine the recrystallization mechanism and the sites of recrystallization nucleation in Metals and Alloys. When a rod is drawn into wire, a bar is forged, or a sheet is rolled, the grains acquire a preferred orientation or deformation texture. When any of these are subsequently heated to a temperature high enough to create a new population of grains, this population also possesses a texture, usually though not always different from the deformation texture. The process of creation of a population of new grains is called recrystallization (since there is no change of phase, this usage differs from geologists' common usage), the treatment is called annealing and the texture is termed an annealing texture. Recrystallization (Rex) takes place through nucleation and growth. Nucleation during Rex can be defined as the formation of strain-free crystals, in a high energy matrix, that are able to grow under energy release by a movement of high-angle grain boundaries. The nucleus is in a thermodynamic equilibrium between energy released by the growth of the nucleus (given by the energy difference between deformed and recrystallized volume) and energy consumed by the increase in high angle grain boundary area. This means that a critical nucleus size or a critical grain boundary curvature exists, from which the newly formed crystal grows under energy release. This definition is so broad and obscure that crystallization of amorphous materials is called Rex by some people, and Rex can be confused with the abnormal grain growth when grains with minor texture components can grow at the expense of neighboring grains with main texture components because the minor-component grains can be taken as nuclei. In this book, a theory which can determine whether grains survived during deformation act as nuclei and which orientation the deformed matrix is destined to assume after Rex is presented. A lot of Rex textures will be explained by the theory. Recrystallization in metals and metal alloys can proceed discontinuously (creation and motion of recrystallization fronts) or continuously (in situ). Recrystallization in situ is often observed during annealing after very high degrees of deformation or small deformations, in materials with a high content of the second phase particles. Recrystallization mechanism in two-phase alloys is in principle not different from the recrystallization mechanism in single-phase alloys. However, the presence of the second phase particles affects significantly the process kinetics. Rex occurs by nucleation and growth. Therefore, the evolution of the Rex texture must be controlled by nucleation and growth. In the oriented nucleation theory (ON), the preferred activation of a special nucleus determines the final Rex texture. In the oriented growth theory (OG), the only grains having a special relationship to the deformed matrix can preferably grow. Recent computer simulation studies tend to advocate ON theory. This comes from the presumption that the growth of nuclei is predominated by a difference in energy between the nucleus and the matrix, or the driving force. In addition to this, the weakness of the conventional OG theory is in much reliance on the grain boundary mobility. This book is intended to determine the recrystallization mechanism and the sites of recrystallization nucleation in Metals and Alloys. When a rod is drawn into wire, a bar is forged, or a sheet is rolled, the grains acquire a preferred orientation or deformation texture. When any of these are subsequently heated to a temperature