| Ti55531(Ti-5Al-5Mo-5V-3Cr-lZr)alloy is a new type of near-beta titanium alloy.It has high tensile strength,good fracture toughness and high hardenability.It is suitable for large bearing members with high strength requirements,good weight reduction effect and landing gear,wings and engine pendants.It is applied to the connecting device between the A380 wing and the pendant.At present the study of Ti55531 alloy mainly focuses on the heat treatmen process and the influence of hot deformation parameters on the microstructure and properties and the systematic analysis of the microstructure and recrystallization mechanism of β phase in heat treatment is lacking.Therefore,this paper first studied the effect of solution treatmen parameters on β microstructure evolution of Ti55531 alloy in the β single-phase region Secondly,the isothermal compression deformation of Ti55531 alloys with two different initial microstructures were performed on a Gleeble-3800 thermal simulator and the thermal deformation behavior of the alloy was studied and the samples after isothermal compression deformation were annealed to study the microstructure evolution during isothermal compression deformation and annealing.The dynamic recrystallization mechanism of β phase during deformation and the effect of a relative β grain recrystallization during annealing are analyzed.Temperature and time of the solution treatment have a significant effect on the size of βgrains when alloy is dissolved in β single-phase region.The average grain size of β phase increases exponentially with the increase of time at 900 ℃.The stress value increases with the increase of strain rate during isothermal compression deformation at 900℃.Meanwhile,the higher the strain rate of lamellar structure,the more likely to appear discontinuous yield phenomenon.The higher the strain rate of the equiaxed structure during deformation,the more equiaxed a phase content.There are two dynamic recrystallization mechanisms in lamellar and equiaxed structure during compression deformation:continuous dynamic recrystallization(CDRX)through a subgrain merging mechanism and discontinuous dynamic recrystallization(DDRX)of grain boundary bowing mechanism.The subgrains and dislocations formed during the deformation of the lamellar structure promote the static recrystallization of the β phase after annealing,so that the β grains are refined and the deformation region disappears after annealing.The equiaxed a phase which is elongated after compression deformation has the tendency of equiaxing after annealing.The equiaxed a phase at P grain boundary and subgrain boundary promotes the recrystallization nucleation of the β phase,but at the same time inhibits the migration of β grain boundary. |
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