Composition Optimization And Microstructure And Mechanical Properties Of High Temperature Alloys For Short-term Use At 650~700℃

The composition of high temperature titanium alloy for short-term use at 650~700℃was optimized through the analysis of microstructures, oxidation resistance and mechanical properties analysis. The ingot of high temperature titanium alloy was prepared by induction skull melting(ISM) in a water cooler copper crucible. The pancake and sheets were obtained by hot forging and hot rolling, respectively. Microstructures and mechanical properties of the pancake and the sheets are also emphasized and discussed. The research results are as follows.The buttons ingots were prepared by using arc smelting technology and the elements contents of Al, Zr, Si were adjusted. The high temperature titanium alloys are near α titanium alloy and the microstructures of the ingots are widmanstatten. The compression experiment at room temperature showed that the strength of the samples tended to increase with the increase of Al and Si contents. Dynamic recrystallization occur during hot compression deformation of all the samples from 1000~1150℃. The true stress-true strain curves show that the maximum flow stress decreased with the increase of the temperature. Furthermore, the high-temperature oxidation behavior results show that the surface oxides were mostly TiO2 and a small amount of Al2O3, and the oxidation kinetic curves follows the parabola-straight line oxidization mechanism. The anti-oxidant property of the alloys was improved by the increase Al content. But with the increase of Zr content, the anti-oxidant property of the alloys was decreased. According to experimental results, the high temperature titanium alloy with the contents of 6.4wt.% Al, 8.0wt.% Zr and 0.3wt.% Si shows better integration properties.The typical microstructure of the ingot prepared by ISM is also widmanstatten. The grains size decreased from center to surface of the ingot along the direction of radius. The tensile properties tests at room temperature shows that the tensile strength reachs to 929.3MPa and the elongation is 0.45%. After solid solution and aging treatment via 950℃/1h+650℃/2h and 980℃/1h+650℃/2h, the aspect ratio of platelet α structure decreased in grains. After solid solution and aging treatment via 1050℃/1h+650℃/2h, the microstructure were changed into acicular widmanstatten structure.The basketweave of the high temperature titanium alloy was refined after hot forging. The tests results of tensile properties at room temperature show that the tensile strength is 1140.8MPa and the elongation reachs to 6.81%. The alloy after forging shows good mechanical properties at high temperatures. The strength and the elongation reach to 769.9MPa and 631.4MPa, 8.94% and 10.01% at 650 ℃ and 750 ℃, respectively. In the(α+β) two-phase region, with the increase of solution temperature, α phases of the alloy were reduced and the microstructure is basket weave. In the single β-phase region, the acicular widmanstatten structure was obtained.The alloy sheets were prepared by hot rolling. The microstructures of the sheets are acicular basket weave. The strength and plasticity along rolling direction are better than that of the transverse direction at room temperature. The sheet after the total deformation of 70% has a higher strength than that after the total deformation of 60%. But the sheet after the total deformation of 60% has a better RT plasticity. After solution in the two-phase region, the microstructures of the sheets are basket weaves. And the double basketweave was obtained after solution in β phase region of the sheets.