Microstructure And Properties Of ?-TiAl Based Alloys Fabricated By Selective Laser Melting Technique

The?-TiAl based alloys are important candidate materials for high temperature applications,especially aerospace and automotive industries,due to their attractive properties such as low density,high specific strength and creep resistance…etc,however,the alloys suffer from low ductility and high temperature oxidation resistance.Selective laser melting?SLM?is an additive manufacturing technique,enables the production of individual metal components with complex geometries layer by layer,according to a 3D-CAD volume model,without the need of part-specific tooling or preproduction costs,which provides a new approach for fabricating difficult-to-machine alloy componentsIn recent years,intensive researches have performed in the SLM?-TiAl based alloys,were investigated the microstructure and properties of?-TiAl based alloys.It was found that the SLM alloys exhibited refined structure due to rapid solidification processing,leading to an improved the strength and ductility.Also the ductility and high temperature oxidation resistance were enhanced to some extent through alloying with B,V,Y,Mo,and Cr elements.However,the enhancement in ductility is still limited.So Nb added amount which aimed to more improve the ductility and high temperature oxidation resistance and applied the electromagnetic stirring to study their effects on microstructure of SLM?-TiAl based alloys.In this research the?-TiAl based Ti-Al-Mn-Nb alloys with different Nb additions were fabricated by selective laser melting?SLM?on the TC4 substrate.The influences of Nb content on microstructure and properties of the alloys were investigated in detail.The results reveal that the alloys consist of?-TiAl phase with tetragonal lattice structure and?₂-Ti₃Al phase with hcp lattice structure,and show a sequential structure change from near full dendrite to near lamellar structure with the increase of Nb addition.Owing to the higher Nb content in?-TiAl phase and the formation of near lamellar structure,the alloy with 7.0 at.%Nb addition has the best combination of properties among the studied alloys,namely,it has not only a high hardness of HV2000,a high strength of 1390 GPa and a plastic deformation of about 24.5%,but also good tribological properties and high-temperature oxidation resistance and the effects of electromagnetic on microstructure of?-TiAl alloys during the solidification process have been studied in details.