Atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of nanoscale plate-shaped second phase particles

Abstract

The feasibility of accurately measuring the size and the volume fraction of nanoscale plate-shaped precipitates by atomic force microscopy (AFM) has been explored. For quantitative evaluations their unhandy geometry is conveniently described by superellipsoids. The experimental alloy Ni₆₉Co₉Al₁₈Ti₄ served as a model system: plate-shaped disordered γ-precipitates form in the L1₂ long-range ordered γ′-matrix. The results obtained by AFM are compared with those derived from transmission (TEM) and from high-resolution scanning electron microscopy (SEM). The agreement between the AFM and the TEM results is good. In spite of the low number of SEM images taken, the same holds for the SEM results. In addition, magnetic force microscopy was applied; its results are acceptable. The main advantages of AFM are (i) the numerical output for all three dimensions, (ii) the simplicity of its operation and (iii) the lower cost of the microscope itself. The first point allows the numerical AFM output data to be directly subjected to automated computer-based evaluations. All present experimental and evaluation procedures are also applicable to cube-shaped particles with rounded edges and corners as found, for example, in γ′-strengthened nickel-based superalloys.

Acknowledgements

The authors thank Mrs. A. Ricker (Institut für Medizinische Physik und Biophysik) for technical assistance in the AFM work and Mrs. L. Rettich (Institut für Materialphysik) and Mrs. G. Kiefermann (Institut für Medizinische Physik und Biophysik) for photographic work. Financial support by the Deutsche Forschungsgemeinschaft and by the research programme MSM 0021620834 of the Ministry of Education of the Czech Republic is gratefully acknowledged.