Density improvement of carbonyl iron compacts by addition of titania powders

The addition of fine titania powders increases the sintered density of carb onyl iron compacts from 6.91 to 7.28 g cm(-3) when the compacts were sinter ed at 1200 degrees C for 1 h in hydrogen. Analysis of dilatometric curves a nd microstructures indicated that titania inhibited the early stage sinteri ng owing to the blocking of the diffusion path of iron atoms. However, the titania powders helped prevent the exaggerated grain growth that usually oc curs during the alpha-->gamma phase transformation. As the compact reached 950 degrees C, a small part of the titania was reduced by hydrogen, and the reduced titanium dissolved into the iron matrix and enhanced sintering. Me anwhile, the remaining titania coarsened, and its effect on sintering inhib ition diminished. The retardation of the grain growth, coarsening of the ti tania at high temperatures, and the diffusion rates enhanced by the reduced titanium resulted in improved final sintered densities of carbonyl iron co mpacts.