MICROMECHANISMS OF DAMAGE AND FAILURE IN POLYCRYSTALLINE MATERIALS FROM X-RAY AND NEUTRON DIFFRACTION

摘要: The room-temperature plastic behavior of several FCC alloys was examined with in-situ neutron-diffraction and polychromatic X-ray microbeam diffraction (PXM). measurements characterize the local dislocation density distribution as a function loading combined modeling, provide insights into damage failure in polycrystalline materials. Both, monotonic-tension low-cyclefatigue experiments were conducted stress. during deformation is discussed light relationship between stress dislocationdensity evolution. observed evolution finds that monotonic tensile low-cycle-fatigue samples have similar densities at small strain, but latter much lower than former high strain. INTRODUCTION: Plastic solids focus intense research due to an increasing demand for high-performance structural Of central importance need understand mechanisms control which ultimately lead failure. recent development powerful neutron sources allows nondestructive materials characterization length scales needed advance our understanding nucleation For example, three-dimensional (3D) submicron strain unpaired dislocation-density distributions are now possible emerging class instrumentation: 3D x-ray crystal microscopes. These instruments use ultra-intense synchrotron advanced optics probe beams. By employing microbeams (PXM) virtual pinhole camera method, called differential aperture microscopy, crystalline phase, orientation (texture) elastic tensor can be measured resolution all directions [Larson et al. 2002; Ice Barabash, 2007]. Neutrons also valuable information about processes used study bulk within gauge volumes sufficiently large good statistical information, avoid surface or geometrical complications. Because neutrons nondestructive, made on single sample, avoids difficulties ex-situ multiple specimen