| Titanium alloys have been widely used in aviation,shipbuilding,chemical industries and biological medicine field because of good mechanical properties and biocompatibility.As the major used with largest market demand,the dual phase titanium alloys are paid more attentions.Since most workpieces of dual phase titanium alloys need to produce by hot processing,it is very important to investigate the hot flow behaviors and microstructure evolution.Thus,the hot flow behaviors and microstructural evolutions of two kinds of typical dual phase titanium alloy?TC4,TC11?were investigated.The hot deformation mechanism under different deformation conditions were discussed in detail..Moreover,the research results are successfully used to analyze the formation mechanism of the microstructures in TC4 alloy friction welded joint.The results of dynamic softening behaviors under different hot deformation conditions showed that the dynamic recovery and dynamic recrystallization are the main softening mechanisms during the hot deformation in the temperature range of single?phase.Furthermore,the discontinuous yielding characteristic at the initial stage of hot deformation is also due to the dynamic recovery in?phases.While the deformed microstructure are mostly composed of equiaxial?phases,the softening mechanism of hot deformation in?phases is controlled by the deformation temperature and strain rate.When the hot deformation temperature is far below the T?point and strain rate is enough high(?=70 s-1),the dynamic recovery and dynamic recrystallization is the main softening mechanism in the hot deformation of?phases.When the hot deformation temperature is close to the T?point at same strain rate,the dynamic transformation of???is the main softening mechanism.The strain rate has great effect on the characterization of such dynamic transformations.Results of the dynamic transformation show that the???transformation occurred along the phase boundary dislocations and intergranular dislocations in equiaxial?phase under the condition of low strain rate(?=10 s-1)and high strain rate(?=70 s-1),respectively.As a result,the equiaxial?phase decreased but kept equiaxed and transformed into?+?laths under the condition of low strain rate and high strain rate,respectively.In addition,the equiaxial?phases will completely transformed to?phases under the condition of extremely high strain rate(??350 s-1)in a remarkably short time.It is found that the dynamic transformation of???can affect the transformed products during cooling stage.The phase transformation of????was found in final quenched microstructures of TC11 alloys after hot deformation.The formation of??phases are contributed to those new?phases generated by dynamic transformation of???.Therefore,the final microstructures in these deformed TC4 alloys show multipolar,multiphase and multi-scale characteristics.The mechanism of dynamic transformation of???was studied.The new generated?laths was found in equiaxial?phase.The equiaxial?phase would transformed into?+?laths after???dynamic transformation.In addition,the R texture{10-11}<11-20>and R1 texture{11-22}<11-23>can be found in the Pole Figure map of equiaxial?phase after dynamic transformation.However,the main deformation texture{10-10}<11-20>in equiaxial?phase disappeared after dynamic transformation???.Based on the relevant microstructures,the characteristics of Pole figure further supports the dislocation a/3<11-20>in prism planes{10-10}and consequent dynamic transformation.Based on the similarity of microstructure and texture between shear compression specimen and linear friction welding joint of TC4 alloy,it is proved that the shear compression specimen can be used to study the microstructure evolution behavior and thermal conditions during friction welding.Furthermore,it is found that the dynamic transformation of???occurs during the friction stir welding of TC4 alloy... |
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