Effect of Ni content on the products of Ni–Ti–B system via self-propagating high-temperature synthesis reaction

Abstract

The effect of Ni content on the products of Ni–Ti–B system via self-propagating high-temperature synthesis (SHS) reaction has been investigated in this research. The results show that the products of SHS reactions consist mainly of TiB 2 and Ni. Besides, the transient phases of Ni 4B 3, Ni 3B, NiB and Ni 3Ti also exist in the final products, which means the SHS reactions of Ni–Ti–B system are incomplete. The change in the content of Ni within the chosen range from 30 to 70 wt.% has little effect on the phase compositions of the final products. However, the sizes of TiB 2 particulates have been greatly influenced by the Ni content. The average sizes of normal TiB 2 particulates are nearly the same and about 4–6 μm when Ni contents are 30, 40 and 50 wt.%. Furthermore, TiB 2 particulates in the products of these three systems present exaggerated growth and their sizes can even reach 10–15 μm. The size of TiB 2 particulates decreases dramatically to 1–2 μm when Ni content increases to 60 wt.% while to 0.6 μm or less at 70 wt.% Ni. The addition of Ni facilitates to form more liquid phases that are beneficial to TiB 2 formation during SHS reaction process. The formation mechanism of TiB 2 in Ni–Ti–B system can be characterized by the solution, reaction and precipitation processes. This can be further substantiated by the presence of remaining liquids, the typical hexagonal-prism morphology and the growth striation on (0 0 0 1) crystal face of TiB 2 particulates.