Study of the Structure and Chemistry of Point, line and Planar Imperfections Via Field-Ion and Atom-Probe Field-Ion Microscopy

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 ≈0.4° of Σ = 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 ( ≈Σ1 = 9 ). These results are consistent with our Monte Carlo simulations of high coincidence twist boundaries and a Σ = 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.