Microstructure Evolution Of Ti-34521 Titanium Alloy In Hot Deformation And Annealing

Because of its high strength,high toughness,corrosion resistance and good forming properties,the application field of ? titanium extends from aerospace to ship and ocean engineering structure.The mechanical properties of titanium alloys are determined by chemical elements and microstructure.For the titanium alloy with the given chemical elements,the mechanical properties are mainly determined by the microstructure.Hot plastic deformation and heat treatment can significantly change the microstructure.Ti-34521 titanium alloy is a new ? titanium alloy applying in ocean engineering with high strength,high toughness and high corrosion resistance.The grain size and crystallographic orientation of ? phase has a significant influence on mechanical properties.Therefore,to investigate the evolution of ? phase in deformation and annealing,Ti-34521 titanium alloy undergos isothermal compression and annealing.The main achievements obtained are as follows.(1)In the single-pass isothermal compression,? grains are elongated.Dynamic recovery(DRV)and dynamic recrystallization(DRX)occur.But the volume fraction of DRX is quite low.DRV is the main softening mechanism.The mechanism of DRX includes continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX).The volume fraction of DRX increases with increasing deformation temperature or reducing strain rate.(2)In the three-pass isothermal compression,the grain size of the original material has a great influence on the morphology of ? grains when the temperature is low,but the influence reduces as the temperature increases.DRX does not occur in the three-pass isothermal compression.Increasing the temperature results in the enhancement of DRV.With the increase of strain,? grains are elongated,the intensity of <001> fiber increases,while the intensity of <111> fiber reduces.(3)While Ti-34521 titanium alloy undergos single-pass isothermal compression and annealing,it is found that the average grain size of ? grains increases with the increase of deformation temperature,and the volume fraction of static recrystallization(SRX)reduces.<001> fiber is the main texture component after annealing,and its intensity increases with the increase of deformation temperature.(4)While Ti-34521 titanium alloy undergos three-pass isothermal compression and annealing,it is found that the volume fraction of SRX reduces.<001> fiber is the main texture component after annealing,and its intensity reduces with the increase of deformation temperature.After the same isothermal compression and annealing,the intensity of <001> fiber in coarse-grain original material is higher than that in fine-grain original material.The microstructure after compression and annealing changes little when the strain increases from 50% to 70%.