Precipitation of ceramic particles in Fe-TiB2 and Fe-Ni-TiB2 cast steels during the sub-rapid solidification process

Abstract

Titanium diboride (TiB2) particle reinforced steels were prepared by a sub-rapid solidification process using the in-situ method. Effects of the Ni concentration on the precipitation of TiB2 ceramic particles were studied and modified in detail. The results show that the mechanically unfavorable-block TiB2-morphologies and the matrix constitutions change with the addition of alloy Ni. The Ni concentration in the iron matrix closes the primary δ-Fe ferrite phase zone, retards the precipitation of the primary TiB2 particles, changes the residual interfacial lattice strain in α-Fe ferrite from tension to compression and promotes the ordered adoption of Fe atoms in (Ti, Fe)B2, which results in the ceramic particles growth into the vermicular-shaped morphologies. Strongly coherent interfaces between a-Fe matrix and TiB2 particles form in Fe-Ni-TiB2 high-modulus steels (HMS) according to the generation of the compression lattice strains at α-Fe ferrite interfaces. The mechanical favorable interfaces are believed to be responsible for the obvious improvements in the mechanical properties, especially the tensile elongation, of Fe-Ni-TiB2 HMS.