Scripta METALLURGICA Vol. 25, pp. 841-845, 1991 Pergamon Press plc et MATERIALIA Printed in the U.S.A. All rights reserved FURTHER STATISTICAL ANALYSIS OF THE COMPOSITION OF A Y~ =-.9/-~(-1,-1,4) GRAIN BOUNDARY IN A Mo(Re) ALLOY STUDIED BY ATOM-PROBE FIELD-ION MICROSCOPY D. Udler, J. G. Hu, S.-M. Kuo, 1 A. Seki, 2 B. W. Krakauer, and D. N. Seidman Northwestern University, Department of Materials Science and Engineering and the Materials Research Center, R. R. McCormick School of Engineering and Applied Science, Evanston, IL 60208-3108, U.S.A. (Received December 4, 1990) (Revised January 29, 1991) Introduction We have recently performed a combined transmission electron microscope CI"EM) and atom-probe field-ion microscope (APFIM) investigation of Re segregation to a single grain boundary (GB) that is within ---0.4"of a E = 9 coincident site lattice (CSL) orientation in a Mo-5.58_+0.31 at.% Re alloy [ 1,2]; specifically the misorientation is 0 =- 38.5" about the c 1 = (1/'-,/2)[1,1,0l i direction, and the plane of the GB is -- (-1,-1,4); this GB is mainly a tilt GB with a twist component. The primary conclusion of our paper [1,2] with respect to GB segregation is that this specific GB studied has an "uncorrected Re concentration which is = 1.27 or 27% greater than the Re concentration of the matrix -- this value represents the minimum segregation enhancement factor, 3 as it includes some solute atoms from the matrix."[3,4] In this letter we recapitulate briefly our experimental procedure, the results obtained, and we then consider in detail the question of the statistical uncertainties involved. This detailed statistical analysis confirms the original conclusions made in reference 1 with respect to the uncorrected Re concentration at the GB, as well as the corrected Re concentration. Recavltulation of Exoeriments Performed and the Results Obtained We now recapitulate briefly the experiments performed and the results obtained. A schematic diagram of the basic geometry employed is exhibited in Fig. 1. For the geometry of Fig. 1 the plane of the GB is parallel to the long axis of the APFIM, and as field evaporation of the FIM specimen proceeds the chemical identifies of the atoms in the individual planes perpendicular to the GB plane are analyzed on an atom-by-atom basis. With the GB plane in this orientation the measurements integrate over the segregation concentration profile that is normal to the plane of the GB interface. The principles of these experiments have been presented and analyzed in detail elsewhere.[3,4] Figure 2 illustrates the three basic measurements made and the results obtained. Figure 2(a) is a reference measurement and is made at a point which is far enough away from the GB -- >10 nm -- that the GB's presence does not affect the value of the Re concentration measured; the Re concentration measured for this case is 5.58_+0.31 at.% Re based on =5680 Mo plus Re atoms. Figure 2(b) is the arrangement used to measure the Re segregation enhancement factor. In this geometry the Re concentration measured is denoted <CgbRe>u , where the u denotes a lCurrent address: Motorola Corporation, Research and Development Division, Phoenix, Arizona. 2Current address: Sumitomo Metal Industries, LTD., Research and Development Division, Osaka, Japan 3That is, it is a lower bound to the actual segregation enhancement factor or excess Re at the GB. 841 0036-9748/91 $3.00 + .00 Copyright (c) 1991 Pergamon Press plc