摘要
采用Gleeble3800热模拟试验机对SP700钛合金进行热压缩试验,研究合金在变形温度为800～880 ℃、应变速率为1～10 s-1、压缩变形量为30％和50％条件下的流变行为及显微组织演变.结果表明,随着变形温度升高和应变速率降低,SP700钛合金热压缩变形的峰值流变应力降低.合金在800℃压缩变形时,流变应力曲线呈明显的动态软化,其显微组织中α片层逐渐破碎球化,部分α片层发生动态再结晶.随变形温度升高,合金压缩真应力-应变曲线呈稳态流变状态.在相同变形温度下,随应变速率和压缩变形量增加,α片层球化程度增加.热变形过程中,平行于压缩轴的α片层在压应力作用下弯曲扭折,片层内取向差不连续存在,并于不连续处存在新α/α界面.垂直于压缩轴的α片层在压应力作用下界面发生起伏,片层内部存在累积取向差.在界面起伏处β相楔入α片层,最终导致α片层的破碎球化.
Abstract
The hot compression test of SP700 titanium alloy was performed using a Gleeble3800 thermal simulation test machine,and the thermal deformation behavior and microstructure evolution were examined in the temperature range of 800-880 ℃,strain rate range of 1-10 s-1,and compression deformation of 30％-50％.The findings reveal that the peak flow stress of the SP700 titanium alloy decreases with increasing deformation temperature but increases with increasing strain rate.At a deformation temperature of 800 ℃,the flow stress curves demonstrate evident dynamic softening features with a rapid decrease in flow stress after the peak stress.By metallographic and scanning electron microstructure observations of the deformed microstructure,the α lamellar is gradually broken and spheroidized,and dynamic recrystallization occurs.With increasing deformation temperature,the induced phase transformation occurs,which leads to the dissolution of the α phase and an increase in the volume fraction of the β phase.The degree of recrystallization of theβ phase increases with several β recrystallization grains at the grain boundaries,whereas the degree of globularization of the α lamellae decreases with increasing temperature.As the deformation temperature increases to 880 ℃,the flow stress curves exhibit steady flow.Recrystallization behavior preferentially occurs in the β grains,while the α lamellar remains flat without globularization behavior.That is,recrystallization of the β phase occurs under the test deformation conditions.For the α lamellae,when the deformation temperature is constant,the degree of spheroidization of the α lamellae increases with strain rate and compression deformation.During the hot deformation process,the α lamellae parallel to the compression axis kink,and the cumulative misorientation is discontinuous inside the α lamellae.At the discontinuous points,the new α/α interface boundary is produced,which causes the formation of unstable dihedral angles.To lower the surface tension energy,the β phase wedges into the α lamellae,which eventually results in the break of the α lamellae.For the α lamellae perpendicular to the compression axis,the interface fluctuates,resulting in continuous cumulative misorientation inside the α lamellae.When the rotation axis of the lamellae changes,a new α/α interface boundary is produced.At the interface fluctuation or the new α/α interface,the β phase easily wedges into the α lamellae by element diffusion,which finally causes fragmentation and spheroidization.Moreover,some of the a lamellae experience a shear deformation,leading to fragmentation under compression.
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