Abstract
Near-α Ti alloys are ideal candidates for high-temperature aerospace, automotive and nautical propulsion systems due to their high strength, low density and good corrosion resistance. However, the maximum service temperature of the well-known near-α alloy Ti6242S is limited to about 540 °C. By adding, for example, intermetallic γ-TiAl based alloy particles to Ti6242S powder a significant increase in yield strength up to 650 °C can be achieved by means of spark plasma sintering, along with sufficient room temperature ductility. In this study, investigations on the underlying strengthening mechanisms were carried out. For this purpose, mechanical tests and detailed microstructural characterization were performed.
Spark plasma sintering at 1150 °C of powder blends with 10 m.% spherical γ-TiAl based powder (<20 μm) leads to a homogeneous dissolution of the TiAl particles in the matrix material and a refinement of the lamellar microstructure. Due to the formation of ordered intermetallic α2-Ti3Al precipitates, which are completely stable up to 670 °C in the newly evolved Ti-8.3Al-1.8Sn-3.7Zr-2.0Mo-0.9Nb-0.08Si alloy (m.%), the creep resistance at 600 °C has been increased significantly. In the B containing variant, it was found that finely distributed titanium borides TiB formed in the Ti6242 matrix and led to an even more pronounced refinement of the microstructure. For B additions of 1 m.%, however, the creep resistance at 600 °C is reduced compared to the other alloys, but the strength is increased up to 500 °C.
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