Activated pressureless infiltration of metal-matrix composites with graded activator content

Metal-matrix composites (MMCs) were produced by activated pressureless infiltration of porous Al2O3 compacts with the presence of elemental titanium as an activator and steel (X38CrMoV5-1) as the metal matrix. The quality of infiltration was subsequently investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results show that poor quality of infiltration is associated with blocking of infiltration channels due to the formation of Ti-rich phases which are accumulated over infiltration depth. To prevent the pores blocking, a layer-graded activator green body in which the activator quantity is decreased with infiltration depth was used. Furthermore, it could be shown that the mechanism based on evaporation/condensation of metal onto activator particles is in agreement with the results of this study.