Study On Preparation Mechanism And Thermal Deformation Behavior Of TiNiNb Alloy Prepared By Hot Isostatic Pressing

TiNiNb shape memory alloy pipe joints have attracted attention in the aerospace industry due to their wide hysteresis effect,no welding,obvious weight reduction effect,easily installation,strong impermeability and excellent comprehensive performance.Especially in the manned space field,large-size TiNiNb shape memory alloy pipe joints are the focus of future research for deep space self-assembly systems.However,the development of large-size shape memory alloy pipe joints has the following problems:molding and processing are difficult;pipe joints generate more waste during machining;the degree of grain size is limited,which seriously affects the mechanical properties and shape memory properties of the pipe joints.The hot isostatic pressing method can solve the above problems.Because of its characteristics of forming complex parts,near net shape forming,and refining crystal grains.This paper made a preliminary exploration for the development and application of large-size TiNiNb shape memory alloy pipe joints.Firstly,the TiNiNb prealloyed powder was mechanically alloyed to explore the mechanical alloying mechanism and obtain better process parameters.Secondly,on the basis of this,a large-sized TiNiNb alloy tube was prepared by hot isostatic pressing process.Then,its microstructure,mechanical properties and martensitic transformation behavior were investigated.Finally,the thermal deformation behavior of hot isostatically pressed TiNiNb alloy tubes was studied.The effects of deformation temperature and strain rate on the thermal deformation behavior were investigated.The thermal deformation activation energy was calculated and the constitutive equation was established.The main conclusions are as follows:?1?In the initial stage of ball milling,the powder particles are not refined,and cold welding and agglomeration occur.As the ball milling time is prolonged,the cold welding and agglomeration phenomenon are reduced.When the ball milling reaches30 h,an amorphous phase begins to appear.In addition,the mechanical parameters of mechanical alloying are:ball to material ratio of 10:1,rotation speed of 400r/min,and ball milling time of 50 h.?2?The hot isostatic pressing process parameters are 1100?,110 MPa,and the heat preservation dwell time is 3 hours to prepare a large-sized TiNiNb alloy tube with a uniform microstructure?inner diameter of 15 mm,outer diameter of 35 mm,height of 100 mm?;The microstructure of the TiNiNb alloy mainly includes TiNi matrix phase,?-Nb phase and a small amount of?Ti,Nb?₂Ni phase.The martensite phase of hot isostatically pressed TiNiNb alloy tube changes into two-step phase transition,but its martensitic reverse phase transition behavior Not obvious.?3?The deformation activation energy of the hot isostatically pressed TiNiNb alloy at 720⁸00°C is 200.448 KJ/mol;the constitutive equation is:e?5??28?6.777?10⁷[sinh?7?.00032s?8?].³⁴⁴⁸exp?7?-200.448/RT?8??4?The Deformation temperature and deformation rate have a significant influence on the flow stress of hot isostatically pressed TiNiNb alloy.The peak stress decreases with the increase of deformation temperature and increases with the increase of strain rate.During the thermal compression process,the deformation temperature rises and the strain increases.The increase in rate causes a slight increase in the content of the TiNi matrix phase and a decrease in the content of the?-Nb phase.