Uchida, Takayuki1, Yanbin Wang1, Shenghua Mei2, William B. Durham2, Mark L. Rivers1, Steven R. Sutton1
1GSECARS, Univ. Chicago
2Lawrence Livermore National Laboratory
APS-GSECARS
We have adopted X-ray transparent cubic boron nitride (cBN) anvils in a modified deformation DIA (D-DIA) to conduct monochromatic diffraction using a 2-D CCD detector (SMART1500). This setup allows us to obtain real-time diffraction data with complete Debye rings that are essential for accurate determination of lattice strains in the deformed sample. Deformation experiments have been conducted on polycrystalline Ta in series with a polycrystalline MgO stress gage to 6.3 GPa in the D-DIA. Ta samples were deformed continuously up to 30 percent axial shortening, with at a constant rate of 2 x 10-5/s, under fixed pressure (i.e. mean stress). Pressure, temperature, sample length, and monochromatic diffraction patterns were recorded repeatedly during the constant-strain rate deformation process. A monochromatic beam with a wavelength of 0.248 Angstrom (50keV) was used for diffraction. We have developed a software package to analyze the 2-D diffraction data. After spatial and flat-field corrections, each 2-D diffraction pattern is converted into a multiple of 1-D patterns, according to a given azimuth angle range (typically binned at 1 degree intervals). The 1-D patterns are then fitted to yield information on the azimuth dependence for each lattice spacing. Lattice strain is then computed based on the well-known theory (A. K. Singh, J. Appl. Phys., 73, 4278, 1993) to convert to differential stress. This approach allows us to examine lattice strain as a function of pressure, temperature, and total plastic strain systematically. With the known pressure and temperature dependence of the elastic constants for MgO, differential stress can be evaluated throughout deformation. Details of the methodology and analysis as well as experimental uncertainties will be presented.