An investigation of Fe-Ni order in a steel
- PDF / 360,215 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 9 Downloads / 171 Views
B.D. BUTLER, formerly with the Department of Materials Science and Engineering, McCormick School of Engineering and Applied Science, Northwestern University, is with the Research School of Chemistry, Australian National University, Canberra ACT 2601, Australia. J.B. COHEN, Professor, is with the Department of Materials Science and Engineering, McCormick School of Engineering, Northwestern University, Evanston, IL 60208. P. ZSCHACK is with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6118. Manuscript submitted May 13, 1991. METALLURGICAL TRANSACTIONS A
These were polished by standard metallographic procedures and electropolished in 40 pct phosphoric acid in glycerine until back-reflection Laue spots were sharp, indicating that damage produced during polishing was removed. The lattice parameter (0.3609(2) nm) was consistent with the composition, E7] as was the Ms temperature of - 170 K. Two measurements of diffuse scattering were made. The first of these was on the MATRIX beamline, X-18A, at the National Synchrotron Light Source, Brookhaven National Laboratory, Brookhaven, NY. The X-ray energy was chosen via two flat Si crystals, as 8100 eV, 230 eV below the Ni K absorption edge, where the scattering contrast between Fe and Ni is enhanced mainly by the difference in the imaginary components of the Fe and Ni scattering factors. Harmonics were eliminated and the beam focused on the sample with a cylindrical Pt mirror. The decay of the incident beam was monitored by following the scattering from a thin Kapton foil in the beam path. A crystal was mounted on a thermoelectric stage and cooled to 228 K (to reduce thermal diffuse scattering). This stage was covered with a thin Be hemisphere, providing a chamber which was evacuated to reduce air scattering and prevent the formation of frost. The chamber was mounted on a four-circle goniometer. Scattering was detected through widely separated scatter and receiving slits to further reduce air scattering and recorded 56 cm from the specimen with a liquid N2 cooled Li drifted solid-state detector. Air scatter contributed less than 1 pct to the counts detected in the coherent region of the spectrum. The air path served to attenuate the lower energy Fe fluorescence. From the energy spectrum, two windows were established, one around the coherent scattering ( - 1 pct of the total) and the second of the entire spectrum which was dominated by the presence of the Fe K~ and K s fluorescence lines. Both regions were recorded for every point examined in reciprocal space. After determining the crystal's precise orientation, measurements were taken at intervals of 0.1 reciprocal lattice units (rlu). The resolution function of the spectrometer never exceeded 0.03 x 0.04 rlu. Data were corrected for the dead time of both the receiving and monitor detectors, spillover from the fluorescence, pulse pileup, and measured beam polarization. The dead time and pileup were particularly severe because of the large amount of Fe fluorescence and accounted for the m
Data Loading...
