Titanium powder (α-Ti; ≤ 20 mm) with and without the addition of amorphous boron (≤1 mm; 0, 3, 10 or 30 at.%) was processed at HP (2.5 GPa or 7.7GPa) and HT (800ºC, 850ºC, 900ºC, 1000ºC and 1300ºC) using toroidal type chambers1. After processing during 15 or 30 min, cylindrical sintered samples (3 mm in diameter and 2.6 mm high) were obtained. The phase composition and the mechanical properties of the samples were investigated as a function of the processing conditions. Vickers hardness (HV) was measured using a load of 9.8 N.
The sintered bodies of pure Ti remained in the alpha phase. They showed HV values above 3 GPa, with a maximum value of 4.5 GPa for the sample produced at 7.7 GPa/1300ºC. These values are very high if compared with those reported for high-purity titanium (0.9 GPa)2, for unalloyed commercially pure titanium (1.6 GPa)2 or even those obtained for Ti submitted to extreme deformation processes (2.5 - 4 GPa)3.
Boron addition higher than 3 at.% promoted the formation of TiB and TiB2 as secondary phases and significant changes in the samples' mechanical properties. For the compacts produced with 10 at.% B at 7.7 GPa/1300ºC for 15 min and 30 min, the hardness was 5.02 ± 0.2 GPa and 5.66 ± 0.11 GPa, respectively, and the only observed phases were α-Ti and TiB. For the samples produced with 30 at.% B, TiB2 was identified in addition to α-Ti and TiB. The measured hardness was 13.0 ± 1.5 GPa and 8.7 ± 0.5 GPa for the samples sintered at 2.5 GPa/1300ºC/15min and 7.7 GPa/1300ºC/15min, respectively.
For all the samples the hardness increasing was mainly associated to a structural distortion of the hexagonal α-Ti phase. This distortion increased for higher processing temperatures and higher B concentrations in the starting powder mixture.
The results indicated that high pressure reaction sintering is a promising alternative to produce highly densified compacts of α-Ti or Ti/TiB/TiB2 with high hardness.
Acknowledgement to CAPES Brazilian agency by the financial support to this work.