RI malig; 
2 Ebi Combination of Atomic Force Microscopy and Electron Microscopy for 
Sailer Quantitative Characterizations of precipitate distributions 
103]. In te 
Men has been M. Göken, K. Durst and H. Vehoff 
eof TRY. University of Saarland, Department of Materials Science, Saarbriicken, Germany 
hon of 7 was 
Abstract 
An Atomic Force Microscope (AFM) is a very useful instrument to determine the topography of 
surfaces on a nanometer range. Therefore this instrument is used to characterize the distribution and 
size of small precipitates in microstructural alloys as carbides in steels or y' precipitates in 
nickelbase-superalloys. The distribution of small carbides with a size of nearly 30 nm is 
investigated in microalloyed steels with an AFM. To determine the chemical constitution of the 
second-phase-particles the AFM investigations were compared with transmission electron 
microscope (TEM) investigations. TEM replicas were used to analyze the elemental composition of 
carbides. The mechanical properties inside ferrite grains and of cementite and ferrite lamellae inside 
pearlitic grains were analyzed with nanoindentations performed in an AFM. 
Introduction 
Second-phase-particles are used to harden materials. Especially in superalloys the y’ volume 
fraction is an important parameter for the high temperature properties of the material. However, 
. stereological particle strengthening is of a great importance in other systems, too, as for example in microalloyed 
Jf mpg steels. Usually the particle distributions of finely distributed precipitates are characterized by TEM. 
üble by TEM However, a relative high preparation effort is necessary for TEM investigations and only small 
portance. The areas around the etched hole in a thin film are imaged. In addition the film thickness is not constant 
ih the TEM in general, which leads to a limited statistics since only small areas are evaluated. The atomic force 
rad applying microscope (AFM) is a relatively new method for characterization of second-phase-particles in 
alloys with high resolution. Areas from the atomic scale up to 100 pm x 100 pm can be examined at 
ambient conditions. Such microstructural characterizations with AFM are described for example in 
[1]. An AFM analyzes sectioned specimens which makes a quantitative evaluation often easier. To 
evaluate tip shape effects on the AFM measurements, direct comparative measurements on the same 
sane’ specimen areas were conducted with an AFM and TEM on thin TEM foils prepared from the 
The franc superalloy Waspaloy [2]. The size of the same particles could be determined with AFM and TEM. 
From the number of precipitates counted in the TEM and AFM images the film thickness of the 
TEM foil was determined, which allowed a reliable determination of the y* volume fraction of 17.4 
%. If the particles are larger than 100 nm tip shape effects have only a minor influence on the 
measured volume fraction and particle size. 
In this study, both methods were used to image and analyze second-phase-particles in steels. 
Microalloyed steels were investigated with an AFM to determine the distribution of pearlite lamella 
and of carbides. The TEM was used to determine the elemental composition of the second-phase- 
particles. Therefore it was possible to identify the particles imaged in the AFM as carbides. 
Nanoindentations are used to determine the mechanical properties of individual phases. 
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