Research On TiAl-based Superalloy Ti-45Al-8Nb-0.3Y Forming Via SLM

TiAl-based superalloy is a new material with broad application prospects in the aerospace field.The coexistence of metal bonds and covalent bonds between atoms makes it possess a series of superior intrinsic characteristics,such as high melting point and low density,good creep resistance,high elastic modulus,excellent high-temperature strength and oxidation resistance,etc.However,the traditional forming method has the problems of difficulty in processing and inability to form complex structures.Therefore,the use of selective laser melting technology to produce TiAl alloy parts with complex shapes has apparent advantages.In this study,Ti-45Al-8Nb-0.3Y,a high Nb contain TiAl alloy,was selected as the research material,and the material was processed by selective laser melting.This study characterized the surface structure of the original powder.The surface structure of the powder was characterized by scanning electron microscope,X-ray photoelectron spectroscopy,and transmission electron microscopy.It was confirmed that the oxide film wrapped the surface of the powder,and the total thickness is 37.1 nm.The structure is divided into two layers.The main component of the outer layer is Al₂O₃ with a depth of 20.4 nm,and the inner layer is mainly Ti O₂ with a thickness of 16.7 nm.The yttrium oxide is widely present in the entire oxide film.The oxide film can effectively increase the laser absorption rate of a single powder.After calculation,due to the coating of the oxide film,the laser absorption rate of a separate powder is increased by 88.84%.At the same time,the introduction of Y effectively regulated the structure of the powder oxide film.In this work,an intermetallic Ti-45Al-8Nb-0.3Y has been successfully fabricated by selective laser melting.The as-printed sample with high relative density(?98.7%)was built by an optimized parameter.The processing map of the original material has been given.When the laser power<150 W,the volume energy density parameters in the range of 33 J/mm³-55 J/mm³can form samples with higher density.When the laser power is increased,the processing map is narrowed,and parameters with the volume energy in the range of 30 J/mm³-40 J/mm³ can be formed quality samples.The structure was characterized.The phase was dominated by the B₂phase(volume fraction was 84.9%),and a small amount of?₂ phase(14.6%)was present,and there was almost no?phase(0.5%).The average grain size is 13.78?m.In this study,Thermo-Calc is used to calculate the unique solidification path of raw materials in the SLM forming process.the solidification sequence is L?L+???+???+?+???₂+?+B₂.It is verified by using The HEXRD test.In which the cooling rate suppresses the eutectic reaction of???+?,and only a tiny amount of?is precipitated.This result matches the print characterization results.In this study,Ti-45Al-8Nb+0.6%Ti N composite powder was prepared by ball milling.The HEXRD characterization found that the results changed the solidification route of the raw materials and conducted SLM forming exploration to obtain a forming with a maximum density of 97.9%Pieces.The grain size of the shaped parts was significantly reduced(down 35.5%),and the average particle size was only 8.89?m.Almost all phases(99.9%)are?₂ phase.In this study,in-situ alloying was used to introduce Si into the raw materials to obtain built parts with evenly distributed elements.The density can reach up to 98.4%,and its structure mainly exists in the form of columnar crystals.The content of the?phase increases,which reduces the plasticity and fracture toughness of the shaped part,affects the resistance of the developed part to cold cracks,and causes the sample to be relatively dangerous edge curling phenomenon.