Study On Principle And Process Of TiNiNb Alloy Mechanical Alloying And Vacuum Hot Press Sintering

TiNiNb alloy is a shape memory alloy with excellent performance.It has the advantages of corrosion resistance,wide hysteresis,and stable memory.It is widely used in many other fields such as aerospace,marine ships,industrial machinery,biomedicine,etc.Development potential.However,the alloy has difficulties in forming and processing,complicated process,low raw material utilization rate,strict requirements on the corresponding machining equipment and process conditions,it is difficult to process large-scale blanks,and the dimensional accuracy is also difficult to meet the current requirements,which greatly limits its Application and development.The use of powder metallurgy such as mechanical alloying+vacuum hot pressing sintering provides a feasible way to solve the above problems.In this paper,the principle and process of mechanical alloying+vacuum hot pressing sintering for large-size TiNiNb alloys are investigated.The main conclusions are as follows:（1）The better process parameters of TiNiNb alloy powder mechanical alloying:ball milling speed is 200 r/min,ball material ratio is 10:1,ball milling time is 70 h,at this time has reached a completely amorphous structure,blindly increase the ball milling time except To a certain extent,the particle size of the powder will be slightly reduced,and only other impurities will be introduced.It does not make much sense to continue to increase the duration.（2）Study its crystallization transformation mechanism:Through DSC detection analysis,it is found that the temperatures T_x,T_g,T_pcorresponding to the crystallization initiation,glass transition and crystallization peak will increase with the increase of heating rate,with significant crystallization kinetics effect.After calculation,the apparent activation energies of glass transition,initial crystallization and crystallization peak are 129.56,134.22 and 317.66 KJ/mol,respectively.The crystallization activation energy E_xobtained by Kissinger equation and Ozawa equation is smaller than the crystal growth activation energy E_p.The results show that the activation energy required for the growth of the TiNiNb amorphous alloy powder crystal during the crystallization process is greater than that required for nucleation.（3）During annealing and crystallization,it reached 575℃ at a heating rate of7.7℃/min.After holding for 30 minutes,it was cooled with the furnace,and the crystallization effect was the best.As the heating rate increases,the crystallization peak shifts to a higher temperature,indicating that there is a kinetic effect during the crystallization process.（4）During vacuum hot pressing sintering,900℃ was used as the hot pressing temperature,the pressure was 35 MPa,the vacuum degree was 1.6×10^-3Pa,and the holding time was 1 h.The microstructure was uniform and the density was 50 mm.The height was 5 mm.Large-scale TiNiNb alloy blanks,its microstructure mainly includes Ti Ni matrix phase,β-Nb phase and trace（Ti,Nb）₂Ni phase.