Porous TiC–TiB 2 –NiAl composites and effect of NiAl contents on pore structure and microstructure

Abstract

Porous TiC–TiB₂–NiAl composites were successfully synthesised by self-propagating high temperature synthesis (SHS) with Ti–B₄C–Ni–Al mixture as reactant. The effects of Ni+Al contents and particle size of B₄C powders on pore structure and microstructure of composites were investigated. The results show that the porous composites are composed of open and closed pores with desired TiC, TiB₂ and NiAl phases. The closed pores are mainly from the decomposition of B₄C particles, while TiB₂ and TiC particles develop at the surface of B₄C particles, which can provide a shell surrounding the remnant B₄C particles and finally form a shell core structure. With the increase of Ni+Al contents, enough melted NiAl is formed during the SHS process. The NiAl liquid can cause the TiB₂–TiC shell to collapse, then lead to the distribution of TiB₂ and TiC particles in the NiAl matrix, and even fill in the space between the shells and cores, which result in the reducing or even disappearing of closed pores, and the increasing of open porosity.