Research On The Selective Laser Melting Of TiAl Alloy

Due to superior properties,such as low density,high strength,high modulus,good oxidation resistance and fatigue resistance,TiAl intermetallic compound has a promising prospect of applications in the field of aerospace.However,its ductility at ambient temperature is very bad,thus TiAl intermetallic compound is very difficult to be machined,which impedes its practical applications.Additive manufacture techniques present obvious advantages on the rapid prototyping of difficult to machine materials and components with complex shape thereby a fine solidification structure can be obtained.In this paper,electrode induction melting gas atomization technology was used to prepare TiAl alloy powder for selective laser melting(SLM)and particle size distribution,composition and microstructure of prepared powder were studied as well.The prepared powder was fabricated by SLM,where the process parameters,forming quality,microstructure and mechanical properties were also investigated.The main research contents and results are as follows:(1)The TiAl powder prepared by electrode induction melting gas atomization technology has high sphericity,narrow particle distribution and less impurity.As the aluminum element was burned in the melting,the main phase of the TiAl alloy powder was ?2.The internal microstructure showed the mixed morphology of the dendritic and the cellular under rapid solidification.The spherical TiAl alloy powder over 300M had good fluidity and can be applied to the SLM technology.(2)The laser energy density in the range of 40-80J/mm3 can realize the formation of the TiAl alloy block by SLM.Relative density of selective laser melted TiAl alloy increased as the laser energy density increased and the maximum density obtained was 94.85%.Cracks appeared in the specimens and the microstructure showed fine dendrite structure which growed along the edge of the molten pool.The distribution of elements in the formed parts was uniform and the Al element was slightly burned.(3)The mechanical properties were influenced by material properties and laser processing parameters.TiAl alloys formed by SLM showed high hardness but poor compression performance.The Vickers hardness of TiAl alloy formed by SLM increased with the increase of laser power and decreased with the increase of scan speed,while scan space had little influence.The compressive strength increased with the increase of laser energy density,but the energy density was not the only factor that affects the compressive strength.When the laser power(P)=80W,scan speed(v)=700mm/s,hatch space(h)=0.06mm and powder layer thickness(d)=0.03mm,the compressive strength was up to 529.1 MPa.(4)The relative density of TiAl alloy increased by 8.6%after annealing treatment.The microstructure the alloy was fine ? grains with a small amount of ?2/? lamellar.The hardness of was increased and the compressive strength of the block was about 50%higher than that of the original block after heat treatment.