TY - BOOK

T1 - Recovery and recrystallization behavior of technically pure molybdenum

AU - Primig, Sophie

N1 - no embargo

PY - 2012

Y1 - 2012

N2 - Molybdenum is a refractory metal with a body-centered-cubic (bcc) crystal lattice and a melting point of TM = 2620°C. Due to its outstanding physical and chemical properties, technically pure molybdenum is nowadays frequently used in electronics and coating-technology besides traditional high-temperature applications. At present, the production of large plates for sputtering targets is of great importance. Sputtered molybdenum layers are applied as diffusion barriers in thin-film transistor liquid crystal displays (TFT-LCDs) and as back electrodes in photovoltaic cells. However, especially the thermo-mechanical processing of the large dimensions required nowadays remains challenging. Due to the absence of a phase transformation, recovery and recrystallization remain the only mechanisms to control the microstructural evolution during processing. Therefore, the aim of present thesis was to gain deeper insights into the more or less unknown deformation, recovery and recrystallization behavior and the corresponding textural evolution during the initial steps of thermo-mechanical processing. This was accomplished by employing compressive deformation of sintered specimens in a high-temperature deformation dilatometer, hot-rolling, scanning electron microscopy (SEM), high-resolution electron-back-scatter diffraction (EBSD) and transmission electron microscopy (TEM). It was revealed that the elevated-temperature behavior is predominantly governed by recovery processes due to the high stacking fault energy of molybdenum. Low temperature pre-recovery seems to facilitate the nucleation of static recrystallization. The recrystallized microstructure and texture subsequent to warm-deformation and annealing is determined by orientation dependent growth advantages of individual subgrains rather than by the nucleation process itself which takes place by dynamic recovery. During hot-deformation molybdenum undergoes strong dynamic recovery which differs from classical discontinuous dynamic recrystallization. The results established by deformation dilatometry are compared to the microstructure, texture, and static recrystallization behavior of a molybdenum plate produced by industrial thermo-mechanical processing.

AB - Molybdenum is a refractory metal with a body-centered-cubic (bcc) crystal lattice and a melting point of TM = 2620°C. Due to its outstanding physical and chemical properties, technically pure molybdenum is nowadays frequently used in electronics and coating-technology besides traditional high-temperature applications. At present, the production of large plates for sputtering targets is of great importance. Sputtered molybdenum layers are applied as diffusion barriers in thin-film transistor liquid crystal displays (TFT-LCDs) and as back electrodes in photovoltaic cells. However, especially the thermo-mechanical processing of the large dimensions required nowadays remains challenging. Due to the absence of a phase transformation, recovery and recrystallization remain the only mechanisms to control the microstructural evolution during processing. Therefore, the aim of present thesis was to gain deeper insights into the more or less unknown deformation, recovery and recrystallization behavior and the corresponding textural evolution during the initial steps of thermo-mechanical processing. This was accomplished by employing compressive deformation of sintered specimens in a high-temperature deformation dilatometer, hot-rolling, scanning electron microscopy (SEM), high-resolution electron-back-scatter diffraction (EBSD) and transmission electron microscopy (TEM). It was revealed that the elevated-temperature behavior is predominantly governed by recovery processes due to the high stacking fault energy of molybdenum. Low temperature pre-recovery seems to facilitate the nucleation of static recrystallization. The recrystallized microstructure and texture subsequent to warm-deformation and annealing is determined by orientation dependent growth advantages of individual subgrains rather than by the nucleation process itself which takes place by dynamic recovery. During hot-deformation molybdenum undergoes strong dynamic recovery which differs from classical discontinuous dynamic recrystallization. The results established by deformation dilatometry are compared to the microstructure, texture, and static recrystallization behavior of a molybdenum plate produced by industrial thermo-mechanical processing.

KW - molybdenum

KW - deformation

KW - recovery

KW - recrystallization

KW - texture

KW - EBSD

KW - Molybdän

KW - Verformung

KW - Erholung

KW - Rekristallisation

KW - Textur

KW - EBSD

M3 - Doctoral Thesis

ER -