Positron Emission Particle Tracking (PEPT) of Inclusions in Metals

Non-metallic inclusions are known to be sites of crack initiation that are detrimental to the mechanical properties of any metal part or component. This research project focused on developing an experimental technique to track and study the movement of a radioactively labeled inclusion within a liquid metal. Oxide particles of alumina, of sizes about 500 μm, were radioactively labelled by direct bombardment with a 35 MeV He3 beam in a cyclotron, and their behaviour during mould filling of Al alloy plate castings made in a resin-bonded sand mould tracked using a portable modular PEPT camera. Experiments involving smaller alumina particles (<100 μm), were also carried out, in which the particles were made radioactive by ion-exchange techniques. In this case the particles were inserted into a low melting point alloy, (melting point 58°C), in order to preserve their radioactivity. These castings were made in an acrylic die. The results showed that the particle position could be tracked within an accuracy of about ± 2-3 mm, although considerable variation in final inclusion position was obtained, attributed to the variability inherent in the mould filling process