| TA19 titanium alloy is a kind of near-? type titanium alloy and is often used as a key component in blade,impeller and other parts of aircraft turbine.The mechanical properties of the titanium alloy are very sensitive to the change of microstructure,and can obtain the ideal tissue by a series of solid-phase aging heat treatment so as to obtain a more excellent mechanical property.In this paper,the evolution of the microstructure of TA19 titanium alloy and the influence of solution parameters on the microstructure of TA19 titanium alloy are studied.The microstructure of TA19 titanium alloy is changed and the change of mechanical properties is investigated by adjusting the solution parameters.The microstructure of the heat treatment is characterized by OM,SEM,TEM and EBSD,and the mechanical properties are tested on the Instron 88.01 million tester.The main conclusions are as follows:(1)When solid solution in the two-phase region belows the ? transformation point,with the increase of solution temperature,the content of equiaxed ?-phase and lamellar ? phase in ?-transformed show a decreasing trend.The water-cooled structure after solid solution mainly consists of primary equiaxed ?-phase and titanium ?' martensite,in the subsequent aging process,the titanium ?' martensite will be decomposed into a fine granular ? phase.With the increase of solution temperature,the ordered arrangement of the secondary ? phases precipitated in the ?-transformation after aging will be beneficial to the improvement the strength of material,but the decrease of the equiaxed ?-phase content will affect the plasticity.(2)By simulating the heating process of the welding,heating up the T? temperature and then holding for a short time,the semi-equiaxed structure,which is a transition structure between the equiaxed structure and the lamellar structure,is shaped.The semi-equiaxed ? phase has the characteristics that the lamellar ? phase grows into the prime ? phase,and the interface between the ?-transformation and the equiaxed ?-phase is blurred.The changes of content of semi-equiaxed ? phase is similarly to the equiaxed ? phase,with the increases of temperature,the content of semi-equiaxed ? phase decreases.In addition,the time is also the controlling factor of the content of semi-equiaxed ? phase: As the holding time increases,the content of the semi-equiaxed ? phase decreases.When the holding time reaches to 300 s,the semi-equiaxed structure is completely replaced by the lamellar ? phase.The lamellar ? phase is controlled by the cooling rate,As the cooling rate decreases,the lamellar which grows into the prime ? phase will be more pronounced.(3)Shortage of holding time,the uneven diffusion of element Mo which can stable beta phase is the key condition for the formation of semi-equiaxed ? phase,The content of Mo diffused into the original equiaxed ? phase during cooling transformation is not enough to form residual lamellar ? phase,When the holding time is less than 150 s,the semi-equiaxed ? phase is formed,that is,there are lamellar ? phase grow into prime ? phase.Semi-equiaxed ? phase nucleation in the ?-transformed and affected by the orientation and number of ?-transformation.The formation of Semi-equiaxed ? phase follows the Burgers orientation relationship: {1120}?//{111}?,and the lamellar ?-phase interspersed into the semi-equiaxed structures has the same or closer orientation to the primary ?-phase.(4)In semi-equiaxed structure,its primary equiaxial ? phase is characterized by better plastic performance,while the content and size of secondary ? phase precipitated in semi-equiaxed microstructure after heat treatment plays a role in controlling the strength of the material.After short-term solid dissolution,the secondary ?-phase of primary ?-phase and the fine secondary ? phase precipitated in the ?-transition structure greatly increase the strength of the material,and the plasticity of the material decreases. |
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