Superplastic deformation behaviour and microstructure evolution of near-α Ti-Al-Mn alloy

[摘要] Superplastic deformation behaviour of conventional sheets of a near-alpha titanium alloy (Ti-2.5A1-1.8Mn) was studied by a step-by-step decrease of the strain rate and constant strain rate tests in a temperature range of 790-915 degrees C. The research found that superplastic deformation is possible in a temperature range of 815-890 degrees C and a constant strain rate range of 2 x 10(-4) to 1 X 10(-3) s(-1) with elongation above 300% and m-index above 0.4. Also, the research identified the optimum superplastic temperature range of 815-850 degrees C and constant strain rate of 4 x 10(-4) s(-1) which provide a maximum elongation of 600-650%. Strain hardening is accelerated by dynamic grain growth at high temperatures of 865 and 890 degrees C. High dislocation activity is observed at super plastic flow in alpha-phase. Constitutive modelling of superplastic deformation behaviour is performed, and possible deformation mechanisms are discussed. It is suggested that grain boundary sliding between the alpha-grains is accommodated by a dislocation slip/creep mechanism.

[发布日期] 2017-12-21

[关键词] Superplasticity;Titanium alloys;Microsize grain structure;Dislocation structure