Characterisation of a cast iron alloy produced with the addition of TiC nanoparticles

The simultaneous improvement of strength, ductility, and toughness in cast iron alloys is a key goal in the metallurgical industry. A promising strategy to achieve that is to modify the alloys by adding nanoparticles (NPs) with high hardness and thermal resistance. An example of valuable NP is titanium carbide (TiC), which has been reported to originate microstructural changes in the Fe-base alloys and to enhance their mechanical properties. A base cast iron with a high Mg content and a low Si content was first produced and then remelted with different additives in a centrifugal casting furnace to cast two medals in a metallic mould. One of them was produced with no addition of NPs and the other one with 3.8% of TiC NPs (about 20 nm in diameter). These NPs were previously introduced in Ni crucibles to promote good wettability (homogeneous dispersion of the particles) and to prevent agglomeration effects. The microstructure and the particles present in each medal were characterized using optical microscopy and Scanning Electron Microscopy (SEM). Both cast medals show a matrix composed of a high fraction of carbides, areas with martensite and low amounts of graphite particles with some having degenerated shape. The casting produced with an addition of TiC NPs comparatively show a microstructure with slightly lower amounts of graphite particles than that in the casting without any NPs addition. These graphite particles are mainly located in the central areas of both castings due to the low solidification rate at that location. For the case of non-graphitic particles, they were analysed using EDS-SEM microanalyses and then classified into six composition classes, very often containing Mg or Ti as main elements. Although the average density of non-graphitic particles are in the range 20000-25000 mm−2 for both castings, the most frequent composition strongly depends on the addition of the NPs. Thus, the highest density of particles corresponds to compounds (Mg, Si, O, P, RE) for the casting produced without NPs addition, while class (Ti, C) is predominant in the case of the casting with the addition of TiC NPs. Further, it is observed that the size of the (Ti, C) particles present in the matrix ranges between 140 and 430 nm, i.e. about 7-20 times bigger than the size of the added TiC particles.