Research On Melting Tracks Of TC4 Titanium Alloy By Electron Beam Melting

Electron beam cold hearth melting(EBCHM)is a metallurgical technology that combines an electron beam heat source with a cold hearth furnace for melting in a vacuum environment.It is widely used in the manufacture of current high-quality titanium alloys because it can effectively eliminate metallurgical defects in titanium alloys by melting at a high melting temperature in a vacuum environment.However,the saturation vapor pressure of the alloy element Al in TC4 titanium alloy is too high,and the high melting temperature in the melting process will cause a large amount of volatilization of Al elements,which will seriously reduce the quality of the ingot.In this paper,based on the three-dimensional finite element analysis model and element volatilization theory,the melting tracks during the electron beam melting of TC4 titanium alloy are researched,different melting tracks of the electron beam heat source are proposed,and the track factors affecting the quality of TC4 titanium alloy ingots are analyzed.In this paper,based on the analysis of the research progress and problems of EBCHM technology and TC4 titanium alloy melting at domestic and overseas,the electron beam heat source melting track was studied for the optimization of melting process.The research results show that the volatilization of Al elements and the removal of Ti N inclusions in TC4 titanium alloy in the process of EBCHM are related to the melting track and the starting point of the track of the EBCHM process parameters-the electron beam heat source.A reasonable electron beam melting trajectory can effectively reduce the volatilization of Al elements and ensure the removal of Ti N inclusions at the same time.In order to predict the temperature field distribution and flow field distribution of the electron beam melting track during the melting process,the temperature field of TC4 titanium alloy specimens under different melting tracks and the flow field in the electron beam bombardment region were simulated and analyzed by numerical simulation method with the ANSYS Fluent simulation software,combined with the thermal property parameters of TC4 titanium alloy in the melting temperature range.The TC4 titanium alloy specimens were melted with different melting tracks.Firstly,a TC4 titanium alloy block with 50 × 50 × 30 mm side length was selected,and equal amounts of Ti N inclusions were filled in five points at equal intervals on the centerline of the 50 × 50 mm plane of the block,and then melting experiments were carried out with different melting tracks and starting points.The remaining content of Al in TC4 titanium alloy specimens after melting was detected by inductively coupled plasma spectrometer(ICP)to compare and analyze the volatilization of Al caused by different melting tracks in different areas of the specimens,and finally the melting track with less volatilization of Al and uniform volatilization in all areas was the snake-type melting track.The final result is that the melting track with less Al volatilization and uniform volatilization at all places is the serpentine melting track.The residual Ti N inclusions inside the specimens after melting with different melting tracks were compared,and it was found that the residual Ti N inclusions in the specimens melted with concentric circle melting track at the edge starting point were the least,and the impurity removal effect of the serpentine melting track could reach more than 50%.The surface scan of the impurity filling position of the specimens after melting with different tracks by energy dispersive spectroscopy(EDS)revealed that the Ti N inclusions were free and diffused in the TC4 titanium alloy matrix after thermal decomposition,and the stirring effect of the electron beam on the melt pool further promoted the diffusion of N elements.However,combined with the effect of different melting tracks on the volatilization of Al elements,the concentric circle melting track at the edge starting point causes a larger volatilization of Al elements.Therefore,the serpentine melting track is the most suitable electron beam melting track in terms of the volatilization of Al elements and the removal effect of Ti N inclusions.