Research On Preparation Of Spherical Ti-6Al-4V Powder Based On RF Induction Plasma Spheroidization

Titanium and titanium alloys which are widely used in aerospace,marine engineering and biomedical fields have excellent properties,such as high specific strength,low density and good biocompatibility.Especially,the rapid development of additive manufacturing has further expanded its application prospects.At present,the development of 3D printing of titanium alloy is mainly restricted by the preparation technology of high quality spherical powder.Therefore,it is of great significance to study a technology that can efficiently prepare spherical titanium alloy powder with high spheroidization percentage,controllable particle size and excellent comprehensive performance.Radio frequency induced plasma spheroidization has many advantages,such as high temperature(～10~4K),high energy density,no electrode pollution and controllable atmosphere,etc.It has a broad application prospect in the field of spherical metal powder preparation.However,researches have shown that this technology has a highly dependent on the composition and particle size of the raw material powder.Therefore,preparation of spherical Ti-6Al-4V powders by combining the pretreatment process and the radio frequency induction plasma spheroidization technology was researched in this article.In this research,the composition,microstructure and particle size distribution of Ti-6Al-4V powder were controlled by mechanical alloying.The particle size distribution and morphology characteristics of the prealloy granulation powder was controlled by spray drying.Finally,the particle size distribution and morphology characteristics of the Ti-6Al-4V powder was controlled by radio-frequency induced plasma spheroidization.The influence of composition structure,particle size distribution and morphology of Ti-6Al-4V powder on plasma spheroidization effect was investigated.The influence of process parameters on plasma spheroidization,such as powder feeding rate,original powder morphology and particle size,and plasma power,were emphatically studied.The main conclusions are as follows:(1)The mechanical alloying process parameters and composition distribution of Ti-6Al-4V powder were studied by high energy ball milling.When the ball to material ratio was 20:1,milling speed was 200 r/min and milling time was 40 h,the prealloyed powder with average particle size of 5μm and uniform composition distribution was obtained.(2)Spray drying technology was used to study the influence of parameters on Ti-6Al-4V granulation powder.When ammonium polyacrylate was 0.2 wt.%,p H was9.3,polyvinyl alcohol was 2.5 wt.%,atomizer speed was 10000 rpm,the Ti-6Al-4V granulation powder with average particle size 69μm was prepared.The powder with good flowability and apparent density can meet the requirements of RF plasma spheroidization.(3)The process control of radio frequency plasma spheroidization for preparation of Ti-6Al-4V granulation powder was studied systematically.When plasma power is 60 k W and the powder feeding speed is 40 g/min,Ti-6Al-4V spherical powder with uniform composition distribution and 98%spheroidization percentage was obtained.And the powder had good flowability and apparent density,which are 33.2 s/50g and 2.53 g/cm3,respectively.(4)The whole process of mechanical alloying,granulation and RF plasma spheroidizing was studied.It provides a new technological route for the preparation of spherical Ti-6Al-4V powder for 3D printing.(5)The spheroidization of powder is divided into four stages theoretically:particle heat absorption,particle melting,melt droplet heat absorption and particle surface evaporation.When the melting behavior of powders in the plasma torch is in the third stage,the spheroidization is the best.