| High strength ? titanium alloy,which have high specific strength and excellent deep hardenability,cold and hot formability and corrosion resistance,is an important structural material in the field of aerospace.With the rapid development of the aerospace industry,higher requirements are put forward for the low-cost and good mechanical properties of ? titanium alloy.In this paper,for a kind of low-cost metastable ? titanium alloy designed independently,the effects of solution and aging treatment on the microstructure and room temperature tensile properties of the alloy are studied,to provide theoretical reference for the practical application of the alloy.The specific contents are as follows:(1)A new metastable ? titanium alloy was designed by using d-electronic alloy design method and Mo equivalent design criteria.Its nominal composition is Ti-4Mo-6Cr-3Al-2Sn(wt%).The Mo equivalent,Bo value and Md value of the new alloy are 10.48,2.773 and 2.361 respectively,all of them are close to commercial grade high strength ?-titanium alloy.(2)After solution treatment at different temperatures,it is found that the structure of the alloy after solution treatment in the(?+?)phase region is composed of primary ? phase and ? phase;with the solution temperature rising above the transformation point,the primary ? phase disappears,and the alloy structure is a single ? phase;with the solution temperature rising,the yield strength and tensile strength of the alloy increase;when the solution temperature is 750?,the fracture elongation of the alloy is maximum value.With the further increase of solution temperature,the elongation of alloy increases first and then decreases.(3)After solution treatment at different temperatures and aging treatment at 500?/4h,it was found that secondary ? phase precipitated in the alloy structure;with the increase of solution temperature,the primary ? phase gradually decreased to disappear,and the size and spacing of secondary ? phase increased;when the solution temperature was 750?,the spacing of primary ? phase was the smallest,and the size and spacing of secondary ? phase increased.At the same time,the continuous ? phase precipitated at the ? phase boundary.When the solution temperature is higher than the transformation point,the secondary ? phase grows parallel to the crystal along with the ? phase of the boundary.With the increase of solution temperature,the strength and elongation after fracture of the alloy increase first and then decrease,and the strength and plasticity of the alloy are the best when the solution temperature is 750?.(4)After aging treatment of different processes,it is found that a large number of secondary ? phases are precipitated in ? phase grains when the aging temperature is higher than 450?;with the increase of aging temperature,the size of secondary ? phase in the grains are not a significant change,but the ? phase in the grain boundary coarsens obviously;the strength of the alloy reaches the maximum when the aging temperature is 500?,and the elongation of the alloy after fracture continues with the aging temperature.When the aging time is 0.5h,there is no large amount of secondary ? phase precipitation.When the aging time is 2h,the size of secondary ? phase in the crystal is the smallest and the number of secondary ? phase is the largest.With the increase of aging time,the secondary ? phase in the crystal is obviously coarse;the strength of the alloy reaches the maximum when the aging time is 2h,and the elongation after fracture is low,and the change is not obvious. |
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