High-Temperature Strength of Titanium Alloys Alloyed with Silicon, Aluminum, and Zirconium in Air
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HIGH-TEMPERATURE STRENGTH OF TITANIUM ALLOYS ALLOYED WITH SILICON, ALUMINUM, AND ZIRCONIUM IN AIR N. Yu. Poryadchenko, M. M. Kuz’menko, I. V. Oryshych, N. D. Khmelyuk, L. D. Kulak, and L. O. Kalashnikova
UDC 669.295:620.193.2
We study the behavior of VT1-0 titanium alloy alloyed with silicon, aluminum, and zirconium in the process of oxidation in air at 800°C for 30 h. It is shown that, as a result of alloying of the alloy with silicon up to 6 wt.%, its high-temperature strength becomes more than two times higher. This effect is connected with the influence of silicon on the diffusion processes in the metal and scale and changes in the morphology of scale.
Titanium alloys are now extensively used in various branches of engineering due to their relatively small density and high corrosion resistance and strength at room and elevated temperatures. At present, recently developed Ti–Si refractory titanium alloys draw especial attention of the researchers [1, 2]. Their operating temperatures can be as high as 700–750°C and even higher. In the present work, we study the high-temperature strength of alloys of this sort with different contents of alloying elements (silicon, aluminum, and zirconium). The alloys were prepared by using the procedure of plasma skull melting. The temperature of a casting mold was equal to 1700°C and the pressure in the melting chamber varied within the range 0.1–0.6 MPa. The temperature of the molten metal and its chemical composition were equalized by electromagnetic stirring. The thermal motion of skull melting was monitored. The mass and temperature of the melt poured into a graphite mold were regulated. The concentrations of the impurities were as follows (%): 0.02–0.06 O2 and 0.22–0.25 C. The alloy was additionally alloyed with silicon (1–6 wt.%), aluminum (3 wt.%), and zirconium (5 wt.%). Cast specimens were not subjected to thermal treatment for oxidation. Specimens 10 × 4 × 3 mm in size were oxidized in a “Derivatograph” device (the changes in the mass were continuously recorded for 6 h) and in a resistance furnace at 800°C [the mass was periodically measured for the entire period of holding (up to 30 h)]. The accuracy of measurements of the mass was 0.1 mg. In the course of the tests performed in the “Derivatograph” device, the specimens were heated together with the furnace (at a rate of 20°C / min). In the electric furnace, they were placed in a chamber preliminarily heated to the required temperature. Prior to testing, the surfaces of the specimens were ground with emery cloth up to micron purity. The high-temperature strength of alloys was evaluated according to changes in their mass ( g / m2). Their oxidation resistances were compared by analyzing the oxidation rates under identical conditions (g / (m2 ⋅ h)). The structure of alloys after oxidation was studied by using transverse microsections prepared according to a special procedure capable of preserving brittle scale on the specimen surface. The microstructure of alloys was studied with a MIM-7 microscope. Their microhardness
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