UCLA

Steels and other iron-based alloys hold great importance in human society, because they are abundant, cost-effective, and have versatile properties, which can be used to fulfill a wide range of roles. As such, increasing the performance and properties of steels is of both technological and commercial interest. Fe-based nanocomposites are often not economically viable due to the high production cost and low production volume, since they are mostly manufactured in solid-state processes that circumvent the reaction issue between liquid steel and its reinforcing phase. To enable a wide application for Fe-based nanocomposites, cost-effective liquid metallurgy processes need to be developed, as liquid metallurgy is the most widely adopted and cost-effective method of manufacture metals and alloys at scale.The overall goal of this work is to study the nanoparticle incorporation, dispersion, and effects in Fe-based nanocomposites by economical processes, especially liquid metallurgy. First, Invar 36 (Fe36Ni) alloy was reinforced by WC nanoparticles. The reactivity in Invar-WC system was suppressed by temperature control method. It was found that only when the processing temperature was significantly below the melting point of Invar, the reactivity can be reasonably managed. However, the Invar-WC nanocomposite had high strength and favorable thermal expansion properties. Second, TiB2 reinforced Fe-Ti-B high modulus steel (HMS) was studied. The dissolution of TiB2 in liquid Fe was suppressed by the combination of solute (elemental Ti and B) saturation and TiB2 nanoparticle addition (nano-treating). When adding TiB2 nanoparticles into a melt that is already saturated in dissolved Ti and B, the dissolution of TiB2 nanoparticles was reduced. The nano-treating process gave rise to an unexpected solidification phenomenon. The nano-treated HMS had significant higher strength and similar ductility comparing with conventional HMS. Finally, theoretical modeling was conducted to examine the interactions between liquid Fe alloys and oxides for a stable dispersion of oxide nanoparticles. Experiments were conducted to validate the theoretical predictions.