Ti3Al-TiB2 COMPOSITES
Marek Kostecki, Krzysztof Biesiada, Andrzej Olszyna Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Annals 4 No. 10, 2004 pages 221-226
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abstract The study is concerned with improving the properties of Ti3Al, in the first place the fracture toughness and resistance to oxidation at high temperatures, by introducing ceramic particles of titanium diboride (TiB2) into its matrix. The technology of the Ti3Al-TiB2 composites involves the following operations: mixing the starting powders, drying the mixture at T = 90oC, granulating, uniaxial pressing at p = 20 MPa, isostatic consolidation at p = 120 MPa, and sintering the samples at T = 1673 K under the pressure p = 35 MPa. The physical properties of the sintered composites, such as the density, porosity, and absorptiveness (determined by the hydrostatic method) were examined (Figs. 3, 4). A qualitative phase analysis of the Ti3Al+40wt.%TiB2 composite has shown that it contains the Ti3Al and TiB2 phases (Fig. 8). After sintering, the Ti3Al+x%TiB2 (x = 0, 10, 20, 30, 40wt.%) composite shows a high hardness of 920 HV10 and a high stress intensity factor KIc = 97 MPa ⋅ m1/2 (value obtained for the Ti3Al+40wt.%TiB2 composite). The oxidation kinetics of the composites was examined at a temperature of 1173 K in an air atmosphere. The oxidation kinetics curves are shown in Figure 9. We can see that, in all the sintered samples examined, the curves have the parabolic character. The value of the parabolic oxidation rate constant Kp is equal to 3.2 10−3 mg2/cm4s in the Ti3Al samples and 5 ⋅ 10−4 mg2/cm4s in the Ti3Al+40%TiB2 samples. The increased strength of the Ti3Al+x%TiB2 composites can be attributed to the presence of the TiB2 ceramic grains. The hardening occurs as a result of the cracks formed in the ceramic phase particles being deflected and bridged. The increased resistance against oxidation observed in the composite added with 40% of TiB2 is probably due to the formation of a solid scale, which protects the substrate against rapid corrosion. Key words: intermetallic phases, intermetallic-ceramic composites, fracture toughness, heat resistance