Wetting and interfacial phenomena in Ni-HfB2 systems

The wettability and reactivity between polycrystalline hot-pressed HfB2 and liquid Ni, Ni-Ti and Ni-B alloys have been investigated by the sessile drop method up to 1520 degrees C. Independently of the sintering aids (B4C, HfSi2), high-temperature interactions led to the formation of a bimodal interface profile, due to the competition between the strong dissolution of HfB2 in the liquid phase and drop spreading along the substrate surface. Ni demonstrates good wetting with the HfB2 substrates (theta = 20 degrees). Compared to Ni, high Ti-containing alloys reveal much faster wettability kinetics with a final contact angle below 10 degrees, accompanied by the formation of an interfacial Ti-rich reaction product. The eutectic NiB alloy shows complete wetting and fast spreading on HfB2 and minor dissolution of the ceramic intc the liquid, a clear indication that higher B contents could optimize the interfacial structure. These results are of practical interest for liquid-assisted composite synthesis and joining of HFB2-based ceramics. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.