Pressureless Sintering of Titanium Diboride with Nickel, Nickel Boride, and Iron Additives

The effect of relatively small additions (1‐5 wt%) of nickel, nickel boride (NiB), and iron to promote the liquid‐phase sintering of titanium diboride (TiB2) has been studied. Carbon also was added to some samples, to reduce the amount of oxygen impurities in the TiB2 ceramics. Green bodies that were formed by uniaxial pressing were sintered in a graphite furnace at 1300°–1700°C, both under vacuum and in a 500 mbar argon atmosphere, and high densities (>94% of theoretical density) were obtained at temperatures greater than or equal to 1500°C. The weight loss of the samples during sintering was shown to be dependent on the densification rate and the final density and was not governed only by the thermodynamics of the system. Significant exaggerated grain growth was observed in samples with nickel, NiB, and iron during sintering at 1700°C. The exaggerated grain growth was observed to be closely related to the oxygen content of the samples and to temperature. The addition of carbon strongly reduced the density and the oxygen content and, thereby, inhibited grain growth. We have proposed that the exaggerated grain growth is enhanced by surface diffusion in a titanium‐oxide‐rich layer on the TiB2 grains.