Material Science with Positrons: From Doppler Spectroscopy to Failure Prediction

Abstract

We describe an alternative approach for a reliable lifetime prediction employing the local concentration of lattice defects as a precursor for fatigue failure. We present positron annihilation spectroscopy (PAS) as a non-destructive technique sensitive for defect concentrations in the range relevant to plasticity in metals.The Bonn Positron Microprobe (BPM), a currently unique device, provides a fine focused positron beam with a selectable beam diameter from 5 to 200 μm assisted by an inbuilt fully functional scanning electron microscope (SEM). Using the BPM, plasticity and fatigue can be measured with a lateral resolution from some microns up to the range of millimeters.Employing laterally resolved PAS and the empirical supposition of a linear relation between the defect concentration and the logarithm of the number of fatigue cycles, the point of failure was successfully predicted on the common carbon steel AISI 1045. For a generalization of the precursor method, a minimal model of fatigue based on a cellular automaton was developed. First results from a one-dimensional implementation are presented.