Influence of atmosphere and carbon contamination on activated pressureless infiltration of alumina–steel composites

Al2O3/steel metal–matrix composites (MMCs) were fabricated by activated pressureless infiltration at atmospheric pressure in different gas atmospheres; N2, Ar and Ar–5%H2. The infiltration quality was evaluated with examination of the microstructure, infiltrated area and remaining porosity. The atmosphere with the best infiltration quality was chosen for improvement of infiltration by varying infiltration parameters such as temperature, holding time and heating and cooling rates. Further improvement was achieved by addition of Si or SiO2 powder to the preform in order to reduce the effect of the residual carbon. The results show that the activated melt infiltration can be successfully done at atmospheric pressure in inert gas.