Preparation And Characterization Of Superalloy Powder For 3D Printing

Superalloy is widely used in aerospace,shipbuilding and special environmental fields because of their excellent heat corrosion resistance,oxidation resistance,high temperature stability and structural stability.Superalloy components have complex structure and strict dimensional accuracy.The traditional casting and forging process has high cost and long construction period,which is difficult to ensure the stability of processing quality.Additive manufacturing technology can realize rapid and complex forming,and obtain alloy parts with better mechanical properties.At present,the research on superalloy additive manufacturing mostly focuses on its composition and process design,while the research on powder is less.The sphericity,particle size distribution and satellite spherical defects of powder have a significant impact on the microstructure and mechanical properties of manufactured parts.The production of metal powder with ideal characteristics is a necessary condition for the development of additive manufacturing.Gas atomization method has the advantages of high yield of fine powder,good sphericity and low oxygen content.At present,it is the mainstream method to produce high-performance spherical superalloy powder.In this paper,different process parameters are selected for numerical simulation and the preparation of superalloy powder by vacuum induction-melting gas atomization.The effect of atomization process parameters on atomization flow field structure and powder properties were studied.The gas atomization model of superalloy melt was established in Fluent software,and the volume of fluid（VOF）model was used to numerically simulate the primary atomization process of superalloy melt:Firstly,the melt at the outlet of the delivery tube contacted with the recirculation gas,the melt flow velocity decreased and began to expand radially to form a liquid film,the liquid film became unstable under the disturbance of gas,and finally broken at the edge of the liquid film to form large-size droplets;Then,the discrete phase model（DPM）was used to simulate the secondary atomization process:under the carrying action of the gas in the recirculation zone,the large-size droplets produced by the primary atomization break-up in the boundary turbulent layer between the recirculation zone and the supersonic main jet area,formed smaller particles,and leave the atomization chamber along the axis with the gas jet.Under different process parameters,the change of atomization pressure and extension length of delivery tube had a direct impact on the droplet size after primary atomization and the particle size distribution after secondary atomization.With the increase of atomization pressure,the velocity in the recirculation zone and stagnation pressure increased.The maximum velocity at 9 MPa was 237 m/s in the recirculation zone and the stagnation pressure was 357 KPa.With the increase of the protrusion length of the delivery tube,the velocity and stagnation pressure in the recirculation zone continue to decreased.When the protrusion length of the delivery tube was 0 mm,the velocity and stagnation pressure in the recirculation zone were the largest,which was 250 m/s and 353 KPa respectively.The protrusion length of the delivery tube had a great influence on the velocity of the recirculation zone,while the atomization pressure had a great influence on the stagnation pressure.The change of atomization process parameters had a great influence on the atomization flow field structure.The decrease of the protrusion length of the delivery tube and the increase of atomization pressure lead to the continuous decrease of the median particle size D₅₀of the powder.The experiment and simulation showed the same trend.With the increase of atomization pressure,the velocity fluctuation and pressure fluctuation at the outlet increased,which intensified the collision between powders,resulted in the decrease of the sphericity of powder and the increase of the number of satellite powders and hollow powders.The flowability and apparent density of powders were the best under the atomization pressure of 8 MPa.With the increase of the protrusion length of the delivery tube,the amount of satellite powder decreased first and then increased.When the protrusion length of the delivery tube was 0.3 mm,the powder had the best flowability,and when the protrusion length of the delivery tube was 0.6 mm,the flowability and apparent density was the best.