Effects of minor additions of elements into Ti1100 on elevated oxidation-resistant properties

Abstract:

The present work intevatigated the composition rule of the near-? Ti alloy Ti1100 using a cluster-plus-glue-atom model for solid-solution alloys, and its cluster formula could be expressed as [Al-(Ti13.7Zr0.3)](Al0.69Sn0.18Mo0.03Si0.12). A new series of alloys by adding minor Hf, Ta and Nb with similar elements substititution in equimolar ratio were then designed, being [Al-(Ti13.7Zr0.15Hf0.15)](Al0.69Sn0.18Si0.1(Mo/Ta/Nb)0.03). These alloys were solid-solution-treated at 950 ℃ for 1 h followed by water-quenching, and then aged at 560 ℃ for 6 h. The microstructures, microhardness, oxidation- and corrosion-resistant properties of alloys were measured. The experimental results showed that the alloy with Hf0.15 substitution for Zr0.15 in Ti1100 still exhibits a ?-transformed lamellar microstructure, while the further combinations of Ta and Nb induce a large amount of equiaxed ??grains to form a duplex microstructure. The change of microstructure doesn’t affect the microhardness of alloys, within a range of 330-370 HV. All the designed alloys, as well as the reference Ti1100, possess excellent oxidation-resistant property at 650 ℃, in which all the oxidation weight gains are less than 1.0 mg/cm2. But the results are obviously different at 800 ℃ in comparison with that of Ti1100, which the oxidation weight gains of the designed alloys with Hf, Ta and Nb co-alloying after 100 h are far less than Ti1100, and the widths of the dense oxidation layers are among 25-27??m. The [Al-(Ti13.7Zr0.15Hf0.15)](Al0.69Sn0.18Si0.1Ta0.015Nb0.015) alloy has the best oxidation resistance with a lowest oxidation weight gain of 2.6 mg/cm2. In addition, this series of alloys also have good corrosion resistance in 3.5 %NaCl.

Key words:near-α Ti alloys; composition design; minor-addition of elements; high-temperature oxidation