Processing and Microstructural Development in Liquid Phase Sintered and Pure TiB sub 2 Ceramics

摘要

The fabrication of TiB sub 2 ceramics with high fracture strength and toughness requires that grain growth and the development of secondary phase(s) be controlled. Liquid phase assisted densification with nickel-bearing metallic additives allows one to achieve high densities and final grain sizes that are comparable to the particle size of the starting commercial TiB sub 2 powders. To gain further reduction in TiB sub 2 grain size studies of hot pressing of submicron TiB sub 2 powders, in which Ni was not added, were conducted. The results showed densification to be enhanced by liquid phases introduced by Ni and Fe impurities (less than or equal to .5 wt % total) but retarded by oxygen levels >1 wt %. Carbon additions led to high densities and significantly reduced grain growth. Using observations of the evolution of secondary phases in the TiB sub 2 -Ni type systems, a model of the densification process is proposed. The model is based on reactions between Ti and B components (resulting from the dissolution of TiB sub 2 ), dissolved oxygen or B sub 2 O sub 3 (present as either impurities or oxide surface layers on the initial TiB sub 2 powder), and the metallic species including additives present in the liquid phase. 17 refs., 6 figs., 3 tabs. (ERA citation 10:051810)