| Nearβtitanium alloy has the advantages of high specific strength,good corrosion resistance,and good biocompatibility.It is widely used in aerospace,chemical,medical and other fields.This paper takes Ti-1023 alloy as the research object,and uses various characterization methods to evaluate the stress-strain behavior,dynamic recovery/dynamic recrystallization（DRV/DRX）,phase transformation characteristics and spheroidization of the lamellarαphase during thermal compression deformation in high and low temperature regions,as well as the phase transformation characteristics under heat treatment and room pre-deformation aging have been studied in depth.When Ti-1023 alloy is compressed at high temperature at 750℃（α+βphase region）,DRV/DRX will occur,and theαphase will be precipitated by dynamic nucleation.When the strain rate is 0.0005 s-1,0.001 s-1,and 0.01 s-1,the peak stresses of the alloy are 37MPa,57 MPa,and 106 MPa,respectively,and the critical stresses for DRX are 35.7 MPa,53.2 MPa,and 100.2 MPa,respectively.When the alloy is compressed at 750℃,the originalβgrains are flattened and a large number of small-angle grain boundaries are formed.Theαphase is preferentially precipitated atβand small-angle grain boundaries,and theα/βorientation relationship is deviates greatly from the Burgers orientation relationship,the Pitsch-Schrader orientation and the Potter orientation relationship.After pre-deformation at room temperature,a large amount of martensite is produced in Ti-1023 alloy.After high temperature（750℃）aging treatment,theαphase is preferentially precipitated in spherical and short rod shapes at the interface of primary martensite and secondary martensite.With the extension of the aging time,the spherical and short rod-shapedαphases merged and grew.When the aging time is 40 min,theαandβphases at the martensite interface do not follow the Burgers orientation relationship,while theαandβphases outside the martensite all follow the Burgers orientation relationship.When the aging time is extended to 60 min,theαphase at the martensite interface and theαphase in other regions follow the Burgers orientation relationship with theβphase.Ti-1023 alloy exhibits DRV and DRX during low temperature（550℃）thermal compression deformation,and a large number ofαphases with various morphologies are precipitated.When the strain rate is 0.0005 s-1,0.001 s-1,and 0.01 s-1,the peak stresses are 423 MPa,496 MPa,and 797 MPa,respectively;the critical stresses for DRX are 339.5MPa,427.1 MPa,and 728.7 MPa,respectively.Theαphase precipitated when the alloy is compressed at low temperature exists in the form of equiaxedα,lamellarα,and a small amount of brokenαphase.In the interior of the slip band,theαphase is densely precipitated in an equiaxed shape,and the area outside the slip band is precipitated in a lamellar shape.A small amount of the lamellarαphase is broken.Theαphase preferentially precipitates small short rod-likeαphases in the primary martensite and the secondary martensite of the Ti-1023 alloy after pre-deformation and subjected to a long-term aging treatment at low-temperature（550℃）.Compared with pre-deformed high-temperature aging,the precipitation ofαphase is more difficult during low-temperature aging,and the size is smaller.The precipitation ofαphase is inhibited during high temperature compression of Ti-1023 alloy.The low temperature compression promoted the precipitation ofαphase.There is an equilibrium point betweenαphase transformation and DRV/DRX.The hot deformation mechanism of Ti-1023 alloy is mainly the dislocation migration mechanism.In addition to the dislocation migration mechanism,the grain boundary diffusion mechanism and grain boundary sliding mechanism also exist in the hot deformation process of the alloy,which are related to the lamellarαphase fragmentation and spheroidization.The three mechanisms work together and promote each other to promote the plastic deformation of the alloy. |
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