Mechanical Properties of Densely Sintered High-Purity Titanium Diborides in Molten Aluminum Environments

Titanium diboride powder, produced in an arc-plasma reactor, was pressureless-sintered to near theoretical density to produce materials of different grain sizes. Mechanical properties in an aluminum environment at 960° to 1000°C were studied by strength vs stressing rate and KIc tests. All materials experienced liquid-metal embrittlement in aluminum containing Fe, Si, and P impurities. During exposure, these metals penetrate TiB₂ grain boundaries and the impurities preferentially segregate there. Fine- and coarse-grained materials exhibited stress-strengthening (negative N ) and stress-corrosion (positive N ) slow crack growth behavior, respectively. Results were interpreted in terms of opposing slow crack growth mechanisms.