SOME ASPECTS OF THE MEASUREMENT OF COMPOSITION IN THE ATOM PROBE

The measurement of compositions in the atom probe has been studied by considering the phase decomposition of high purity Fe-Cr alloys. Alloys containing 45% Cr were aged for up to 500h at 500°C in order to study the early stages of the decomposition. Typical data representations are considered as fractals. The scaling exponents have been measured for different aging conditions and three different scaling regimes have been identified. The consequences of the fractal nature of the profile are discussed. The results indicate that there is an optimum block size at which the composition and other physical parameters may be reliably measured. The cumulative plot is shown to be a fractional Brownian motion suggesting that the simulation of the microstructures by randomly placed spheres is not consistent with the observed microstructures