| High-temperature near-cc Titanium alloy is one of the important structural materials in aircraft engine due to its comprehensive mechanics performance as well as good oxidation-and corrosion-resistance. In order to satisfy causative perfromance, multiple elements are added simultaneously into the base Ti, including HCP-α stabilizer Al, BCC-β stabilizers Mo, Nb, Si, neutral stabilizers Zr, Sn and rare earth elements Y, Ce and Nd. The Al equivalent method, d-electron theory, electron concentration criterion and BP nepal network were put forward to design high temperature Titanium alloys because of multi-element composition complexity and making sure structure stability of Titanium alloys. Near-α Ti alloys are solid solutions, on the basis of local chemical short range, our group proposed a cluster-plus-glue-atom model for stable solid solutions to explore the rule of near-α Ti alloys composition. This model contains a cluster part and a glue atom part, where the clusters are nearest-neighbor polyhedrons with strong interactions and glue atoms are located in-between the clusters with weak interactions. The cluster formula can be written as [Cluster](Glue atom)x(x is the number of glue atoms). The present work investigated the composition rule of the typical near-α Titanium alloy Til100 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), x=1. Three new series of alloys by adding minor Hf, Ta and Nb with similar elements substitution in equal-mole mode were then designed, being [Al-(Ti13.7(Zr/Hf)0.3)](Al0.69Sn0.18Si0.1(Mo/Ta/Nb)0.03), Zr0.3, Hf0.3 and Zr0.15Hf0.15 respectively. These alloys were solid-solution-treated at 950℃ for 1 h followed by water-quenching, and then aged at 560℃ for 6 h. XRD and OM were used to examine the phase and microstructure of alloys. The experiment of high temperature oxidation-resistant was tested in muffle(KSL-1400X-A2) at 650℃ and 800℃. EMPA was used to test the widths of the dense oxidation layers and elements distributions. The corrosion resistances were studied in 3.5% NaCl solution by Garmy electrochemical workstation. And MTS was used to test tensile properties.The experimental results showed that the adding of Hf, Ta and Nb reduced β structure stability and formed duplex microstructure. The change of microstructures didn’t affect the microhardness of alloys, within a range of 330-370 HV. Strength and plasticity of extension normal tensile property were better than Til100. Strength extension in 650℃ was as good as the reference alloy while the plasticity was greatly enhanced. Al-(Ti13.7Zr0.3)-(Al0.69Sn0.18Moo.oiTao.oiNb0.01Si0.1) in Zro.3 series had the excellent oxidation-resistance both at 650℃ and 800℃C with 5.6 mg/cm2 oxidation weigh gain and 17 μm oxdaition layer, small corrosion potential, the same high temperature tensile strength 550 MPa and better pyroplasticity 8=23% compared to Til 100. High temperature oxidation-resistant were enhanced obviously with Hfo.3 substitution for Zro.3. Al-(Ti13.7Hfo.3)-(Al0.69Sn0.18Ta0.015Nb0.015Si0.1) had the strongest antioxidant capacity at 800℃ with 5.6 mg/cm2 oxidation weigh gain and the widths of the dense oxidation layers just 15 um. In Zr0.15Hf0.15 series, the combinations of Zr, Hf, Ta and Nb induced a large amount of equiaxed a grains to form a duplex microstructure. It possessed good comprehensive properties and better high temperature oxidation-resistance than Ti1100, but inferior to Hfo.3 serial alloys. |
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