Study of the Structure and Chemistry of Point, Line and Planar Imperfections Via Field-Ion and Atom-Probe Field-Ion Micr
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STUDY OF THE STRUCTURE AND CHEMISTRY OF POINT, LINE AND PLANAR IMPERFECTIONS VIA FIELD-ION AND ATOM-PROBE FIELD-ION MICROSCOPY DAVID N. SEIDMAN Northwestern University, Department of Materials Science and Engineering and the Materials Research Center, The Technological Institute, Evanston, Illinois 60208-3108, U.S.A.
ABSTRACT We first list, in catalogue form, a number of research subjects which have utilized the fieldion microscope (FIM) and atom-probe field-ion microscope (APFIM) techniques in their solution. Then we present the results of a combined transmission electron microscopy (TEM) and APFIM study of a grain boundary (GB) in a Mo-5.4 at.% Re alloy, which had been annealed in bulk form for 35 hours at 1273 K to induce Re segregation. A GB with an orientation within --0.40 of I = 9 was studied employing TEM and analyzed in detail using Bollmann's 0-Lattice theory and Frank's formula. A set of secondary GB dislocations was observed with a spacing of 11.4 nm. The APFIM measurements -- on this same GB -- indicate that it has a Re concentration of =9.8 at.%; this value is 1.75 times greater than the matrix's measured concentration of 5.6±0.9 at.% Re. Thus this research constitutes direct and quantitative experimental evidence for solute-atom segregation to a high-angle grain boundary with a relatively high degree of coincidence ( =1 = 9 ). These results are consistent with our Monte Carlo simulations of high coincidence twist boundaries and a Y = 5 tilt boundary in Pt-1.0 at.% Au alloys which show that solute-atom segregation occurs mainly to the dislocation cores. The experimental and simulated values of the enhancement factor are approximately the same.
INTRODUCTION The field-ion microscope (FIM) allows for the routine observation of individual atoms in direct lattice space. The FIM is a point-projection microscope and, hence, no lenses are required for the formation of an image. The entire image is approximately a stereographic projection of the atoms which reside at the surface of a sharply-pointed tip (=10 to 60 nm in diam). When an FIM is combined with a time-of-flight mass spectrometer--to form an "atom probe"--it is possible to determine the mass-to-charge state ratio of individual ions, one at a time. Both instruments were invented by the late E. W. Mfiller [1]. The FIM and the APFIM have been used extensively to study, for example, precipitation phenomena [2,3], surface diffusion of adatoms [4,5], radiation damage [6], order-disorder alloys [7] and solute-atom segregation [8 -10]. In this paper we first list, in catalogue form, the applications of the FIM and the APFIM, of mainly our group, to a number of research topics. And then we discuss in detail a combined APFIM and classical transmission electron microscope (CTEM) study of Re segregation at a grain boundary (GB) which is within -=0.4o of a I = 9 orientation in a Mo-5.4 at.% Re alloy, which had been annealed in bulk form for 35 hours at 1273 K to induce Re segregation. At 1273 K the solid solubility of Re in Mo is =27.8 at.% Re. It is shown that
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