Research On Microstructure And Properties Of The New High Strength Structural Titanium Alloy

Titanium alloy has been widely used in spaceflighta, ships and weapons for itsexcellent properties such as low density, high specific strength and good anticorrosion.With the aviation aircraft is increasingly demanding on the properties of bearingcomponents, therefore, it has become a research hotspot about improving theperformance of structural titanium. The paper, with high strength titanium alloy as theresearch target, has designed new type of high-strength titanium alloy composition. Theeffect of heat treatment and hot deformation on the microstructure and properties ofthree titanium alloys by optical microscope, electric scanning microscope, XRD, microhardness and tensile testing machine was analyzed. The main contents and theconclusions of the research were as follows:This paper designed three new type Ti-Al-V-Mo-Cr-Zr-Fe-Nb titanium alloys inaccordance with alloying principle and beta titanium alloy design principle. Themolybdenum equivalent of the1#,2#and3#are21.0,19.0and14.2alloys respectively.The three alloys had fused cast three times according to the design elements by thevacuum self-consuming smelting technology. It has homogeneous distribution of alloycomposition after three times of smelting. Consistent with the theoretical designcomposition, the impurity content of alloy was lower than the standard. The grain sizeof as-cast alloy was thicker, the grain size of which was800~1200μm. When themolybdenum equivalent of aolly decreased, a-phase content was increasing. It wasdetermined the transformational point of1#,2#and3#that was705±5℃、720±5℃and785±5℃respectively by the calculation, continuous heating-up and DTA method.Alloy precipitated a large number of primary-phase after cumulative deformationof60%crude forging. The content of rough forging bar cross-section edge a-phase was more and smaller than that of centre. The content of alloy primary-phase wassignificantly reduced after precision forging. Comparison with three alloys forging stateorganization found that the content of3#alloy a-phase was significantly higher than1#and2#. It showed that the lower alloy molybdenum equivalent, the more primary-phase content in the same forging conditions.The three alloys structure was mainly flat irregular beta phase grain after800℃hotrolling. The2#and3#alloys respectively contained granular and acicular a-phase. Itmeasured tensile strength of1#,2#and3#alloys was respectively890MPa,957MPaand861MPa, and elongation of that was respectively20.0%,27.0%and17.5%. Bycomparison, it found that the tensile properties of the2#was better than1#and3#.It measured tensile strength of1#,2#and3#alloys was respectively1412.8MPa,1428.5MPa and1404.5MPa, and elongation of that was respectively8.5%,10.16%and11.92%, by different solid solution plus aging heat treatment. Results showed that, forthe design of three alloys, tensile strength of that could attain all over1400MPa, andelongation of that was not to be less than8%by working out reasonably heat treatmenttechnology. By comparison, it found that the matching strength and plasticity of the2#was better than1#and3#.