| The service temperature and strength of the near a type titanium alloy of traditional Ti-Al-Sn-Zr-Mo-Si system have no enough room to improve,(α+β) two-phase titanium alloys could be serviced in the environment of high-temperature and short-time due to their outstanding solid solution strengthening. At present, some new application areas such as the modern national defense and aerospace have an urgent requirement for high-temperature, short-term and high-strength titanium alloy. Therefore, A Ti-Al-Sn-Zr-Mo-W system martensitic (α+β) two-phase new (short-term) high temperature titanium alloy has been newly developed by Northwest Institute for Nonferrous Metal Research. In order to improve the heat strength under the service conditions of high temperature and short-time, high melting point elements of Mo, W and other alloying elements have been added. The new alloy Mo equivalent is8.53, Al equivalent is4.56, β stability factor Kβ=0.42.In this paper, in order to explore the level of performance of the alloy, supply some theoretical support for the high-temperature titanium alloy in the practical application and performance optimization, and provide technical reference for finding a suitable forging and heat treatment craft to improve the service properties of the alloy, the microstructures, tensile properties and hardness of the new developed (short-term) high temperature titanium alloy after treated by simple annealing and solution+aging were studied by OM, SEM, TEM, XRD and other research methods, the effect of the craft on the microstructure and properties of the new high temperature titanium alloy were analyzed and the thermal stability, oxidation resistance within the range of600～800℃of the alloy treated by solution and aging were defined. So, this work has great theoretical significance and practical value.It was found that, with the annealing temperature elevating, the properties of the alloy at room temperature have little variation, and the high temperature tensile properties at700℃obtained obvious improvement, while the microstructure of the alloy exist some heterogeneity during the process of annealing. The microstructures of the alloys treated by solution+aging treatment were more uniform than that treated after simple annealing treatment. Because the solution temperature, cooling rate after solution and aging temperature have different effects on the numbers, sizes and distribution of β phase, primary a phase and secondary a phase, the effects on the mechanical properties of the new alloy at room temperature and700℃were more complex. To sum up, optimum mechanical properties were obtained by the heat treatment of970℃/1h, AC+600℃/4h, AC, and the room tensile strength, elongation and area reduction rate of the alloy are1310Mpa,13.5%,37.0%, respectively; the tensile strength, elongation and area reduction rate are485Mpa,54.0%and99.0%at700℃. The oxidation rate exponent n values of the new (short-term) high temperature titanium alloy exposed in air at600℃,700℃and800℃are1.43,2.43and1.36respectively. When the alloy exposed in air at600～700℃, the oxide films formed on the surface had good adhesion with substrate, and the oxidation daynamic curves basicaly obey to the parabolic law; while the oxide films fallen off seriously, the oxidation daynamic curves approximately agree with parabolic-straight lines at800℃. The oxidization layers are composed of rutile typed TiO2and small amount of Al2O3. Al2O3films formed easily at high temperature, the higher the oxidation temperature, the larger of the area of the Al-poor areas in sequent surface, the lower of Ti content on the surface. The microstructures of the new (short-term) high temperature titanium alloy exposed in air at600～800℃for100h were similar to that for50h, this proved that the organization of the alloy has thermal organizational stability at600-800℃. Amount of precipitated phases Ti3Al appear on the surface of the alloy during exposed in air at600℃for100h, and the precipitated phases Ti3Al will dissolve gradually when the thermal temperature elevated up to700℃.For the presence of brittle oxygen-rich layer on the surface of the sample with oxidized layer, the room temperature tensile properties of the sample without oxidized layer are superior to that with oxidized layer. With the elevating of thermal exposure temperature, the tensile strength of the alloy with oxidized layer and without oxidized layer show a downward trend, the plasticity of the sample with oxidized layer has lowered significantly, and the plasticity of the sample without oxidized layer has increased a little. |
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