Dresden 2006 – wissenschaftliches Programm
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MM: Metall- und Materialphysik
MM 4: Phase transitions I
MM 4.1: Vortrag
Montag, 27. März 2006, 10:15–10:30, IFW D
AFM, TEM and SEM studies of nano-scale plate-like precipitates — •Dietmar Baither1, Ihor Sobchenko1, Josef Pesicka1, Thomas Pretorius1, Volker Mohles2, Werner Stracke3, Rudolf Reichelt3, and Eckhard Nembach1 — 1Institut fuer Materialphysik, Universitaet Muenster — 2Institut fuer Metallkunde und Metallphysik, RWTH Aachen — 3Institut fuer Medizinische Physik und Biophysik, Universitaet Muenster
The high strength of many structural materials derives from coherent nano-scale precipitates of secondary phases, for example Guinier-Preston zones in aluminium based alloys or γ′ precipitates in nickel based superalloys. Their shape, size and volume fraction crucially determine the strengthening effect. An alloy with the composition Ni69Co9Al18Ti4 was used as model system to determine these parameters for nano-scale plate-like precipitates. Such precipitates of the disordered γ phase arise in the L12-long-range ordered γ′ phase of the matrix after 333 h annealing treatment at 1173 K. From TEM micrographs an approximate mean edge length of 400 nm and a thickness of 40 nm of the precipitates were determined. A precise description of their shape was derived using super-ellipses. The main task was to attain comparable results by AFM. These investigations revealed that the electrolytic etching of the surface attacks preferentially the plate-like precipitates so that deep dimples are formed. Problems and limitations of the AFM characterization of this morphology will be discussed.