Research On The Heat-treatment And Microstructure Evolution Of New Metastable β Titanium Alloy Ti-1300

Ti-1300is a recently developed near β titanium alloy by Northwest nonferrousmetal research institute, which is expected to apply for aircraft structural componentsbecause of its best matching of high-strength and high-toughness, and also itsdeep-hardenability. And in the last couple of years, the application of near β titaniumhas significantly increased and occupies more and more market share in aerospaceindustries as for their outstanding mechanical properties. However, it would bespecially mentioned that the properties of Ti-1300alloys are critically dependent onthe microstructure, demanding a detailed research of microstructure evolution. Theperformance of titanium alloys may vary over a wide range by heat treatment.In this study, the microstructure changes of Ti-1300alloy, including theoriginally forged sample, the solution treated condition (β-solutionized and(α+β)-solutionized) and the quenching and aging type heat-treated samples have beeninvestigated in detail using SEM and TEM to better understand the microstructuredevelopment. In the as-forged alloy, the twinning deformation behavior occurred inthe primary α phase, the β→α phase transformation also been found in the base βphase. During the (α+β)-solutionized condition of the forged samples, the twinning αplates are still present in the residual α phase. The twinning α phases has two differentvariants, the α1variant is rotated about60degree with respect to α2variant, and thetwo variants have60degree angle twinning relationship with the base α phase, theorientation relationship can be described as follows:：{1120}孪生//{1120},0001孪生//1101。The aging characteristics of Ti-1300alloy are similar to theother near β titanium.For the furnace cooling process, there is only one α phase variant generator in thegrain boundary, a variety of α crystalline phase variant generator in Intragranular andhave a cluster distribution. Internal grain boundary α-phase precipitates along thegrain boundaries is only one of side, and with the orientation of the substrate βBurgers relationship was no direct relationship with other grains. Grain boundary αnucleation points may be two, a case is formed inside the grain boundary nucleation,growth of the grains to; another situation near the edge of the grain boundarynucleation, to grow grains.An FCC phase is precipitated in α-phase when β solution treated and cooled toroom temperature.Additionally, in order to better understand the influence of ω phase on nucleationand growth of α precipitates, a two-stage aging process is designed. Thehigh-resolution TEM well shows the growing procedure of α precipitates. These results indicate that α precipitates initially nucleating along the ω phases boundaries,and growing by consuming ω phases until they are disappeared.