| Ti-6Al-4V alloy has excellent comprehensive properties such as low density,high strength and high temperature resistance,and has broad application prospects in many fields such as aircraft manufacturing,oil exploitation,automobile armor and biological medical treatment.However,due to the poor processing property of Ti-6Al-4V alloy,it is difficult to achieve high efficiency and low cost production of titanium alloy by traditional processing techniques such as extrusion forging and smelting casting,which greatly limits the wide application of titanium alloy.In recent years,3D printing technology has developed rapidly,which has the advantages of short manufacturing cycle,material saving and energy saving.It is very suitable for manufacturing complex parts of titanium alloy,and the quality of titanium alloy powder plays a decisive role in the promotion and application of 3D printing of titanium alloy parts production and manufacturing.In this experiment,the technique of radio-frequency plasma spheroidization combined with metal reduction was used to explore the preparation method of low oxygen spherical Ti-6Al-4V powder suitable for 3D printing.The main conclusions obtained during the experiment are as follows:(1)Investigation of radio frequency plasma spheroidization of Ti-6Al-4V alloy powder.This section systematically studied the effects of the process parameters(plasma power,powder feeding rate)of RF-plasma spheroidization on the physical properties(flowability,apparent density)of Ti-6Al-4V powder.When the spheroidizing power is 60 kW and the feeding rate is 80 g/min,the spherical Ti-6Al-4V powder with the best properties can be obtained,and its flowability and apparent density are 28.01 s/50g and 2.43 g/cm~3.When the spheroidization power is 60 kW and the feeding rate is 140 g/min,the higher spheroidization rate and the lower mass loss rate can be obtained.After optimizing the process,the spheroidization rate can reach98.7%.(2)For the problem of Ti-6Al-4V powder have high oxygen content after spheroidizing,analyzes the distribution and the metal powder surface oxygen reduction principle,system explores the calcium content in calcium thermal reduction process,reduction temperature,holding time and pickling process acid concentration,solid-liquid ratio,pickling time,pickling temperature,oxygen content of alloy powder.The optimal process parameters of calcium reduction were optimized as follows:the addition amount of calcium particles was m Ca:m Ti-6Al-4V=2:1,the reduction temperature was 850℃,and the holding time was 2 h.The optimal pickling process was as follows:pickling temperature 40℃,hydrochloric acid concentration 5%HCl,pickling time 80min,solid-liquid ratio 1:6.Through the process optimization,the spherical Ti-6Al-4V powder with oxygen content of 1240 ppm was prepared,and the oxygen reduction rate reached 73.17%,which solved the problem that the spherical Ti-6Al-4V powder could not be used because of the high oxygen content.(3)The mechanism of calcium reduction was deduced.In the process of calcium reduction,the spherical Ti-6Al-4V powder oxide layer reacts with calcium vapor,and micro-cracks are formed on the powder surface.These micro-cracks provide diffusion path for calcium vapor,making the oxygen in the spherical Ti-6Al-4V powder further react with calcium vapor.(4)The sintering properties of spherical Ti-6Al-4V alloy powders were studied.The effects of sintering temperature and sintering time on the morphology,density,mechanical properties and phase of the sintered alloy were studied.When the sintering time is 2 h,the hardness of the sintered Ti-6Al-4V alloy increases with the increase of sintering temperature,and reaches the maximum of 424.69 HV at 1300℃.At the sintering temperature of 1400℃,the hardness decreases due to the growth of the alloy grain and phase transformation.In addition,when the sintering temperature is 1300℃,the density and hardness increase gradually with the extension of holding time,and the hardness reaches the maximum of 557.72 HV when the holding time is 6 h. |
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