Combustion Foaming of Al-Ti Intermetallics Studied In situ by Fast X-ray Radioscopy

Combustion foaming of Al-Ti intermetallics was observed in-situ by X-ray radioscopy at the Technical University Berlin, Germany, and at the experimental station ID-19 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The acquisition rates were 6.7 fps and up to 500 fps, respectively. This allowed for observing in detail the internal structure development during combustion foaming of extruded Al-Ti powder compacts made with Al/Ti molar ratios of 3, 4 and 7 and containing 10 and 20 vol.% exothermic agent (Ti + B4C). At the beginning of the foaming process, μm-sized pores were observed. Foam shrinkage and pore coarsening started immediately after the combustion process. Specimens made with an Al/Ti ratio = 7 showed pore coarsening and a longer solidification time. Specimens with 10 vol.% exothermic agent experienced less volume expansion and pore coarsening than specimens with 20 vol.% exothermic agent. The specimens with an Al/Ti ratio = 4 contained fewer micropores than the one with an Al/Ti ratio = 3.