Quantitative characterization of second-phase particles by atomic force microscopy and scanning electron microscopy

It is demonstrated that the surface analysing methods atomic force microscopy (AFM) and scanning electron microscopy (SEM) can be used to determine accurately the average radius r and the volume fraction f of fine (r approximate to 100 nm) spherical particles of secondary phases. Moreover the distribution function of the radii of individual particles can be accurately established by AFM and SEM. This has been exemplified for gamma'-precipitates in the commercial nickel-based superalloy Nimonic PE16. AFM images have to be corrected for two effects: firstly, for the finite size of the tip and, secondly, for the attack of the gamma' particles by the polishing agent. Owing to this latter effect the radii of curvature of the caps of the gamma' particles protruding from the surface of the specimen differ from the true radii of the gamma' particles. The results for f and r obtained by AFM and SEM are in excellent agreement with those gained by transmission electron microscopy.