Effects Of Y And Mo On Microstructure And Properties Of Laser Additive Manufacturing Of TiAl Alloy

TiAl alloy compared with other high-temperature alloys material with low density,high strength,high stiffness,corrosion resistance,creep resistance,oxidation resistance,good high-temperature performance,and many other outstanding features,which expected to be within the range 600℃to 1000℃partly replacing nickel base superalloy.TiAl alloy can meet the demand of light in the field of aerospace due to greatly improve the sages,which is a kind of new high-temperature structural material with great application and development prospect in aerospace field.However,the room temperature brittleness of TiAl alloy limits its wide application.This work is based on Ti-48Al-2Cr-2Nb alloy,using laser additive manufacturing（LAM）technology to prepare single channel deposition layer with different process parameters,according to its macro morphology and cross section size,determine the best forming process.Thin-walled Ti-48Al-2Cr-2Nb alloy samples with different contents of Y element（0 wt.%,0.5 wt.%,1 wt.%,1.5 wt.%,2 wt.%,and 4 wt.%）and Mo element（0 wt.%,2wt.%,4 wt.%,6 wt.%,8 wt.%,and 10 wt.%）were prepared.The effects of Y and Mo contents on the microstructure and properties of TiAl alloy were investigated,and the appropriate methods to improve the plasticity at room temperature and tensile properties at high-temperature were discussed.The main conclusions are as follows:Rare earth Y can effectively refine the grain size of Ti-48Al-2Cr-2Nb alloy.The precipitates in the TiAl alloy after Y addition are Y₂O₃and YAl₂phases,which hinder the grain growth and refine the grain during the solidification process.The amount of precipitates in the alloy increases with Y content,and the morphology changes gradually.When the Y content reaches 4 wt.%,the precipitates are connected to a network structure,and the hardness reaches the maximum about 402.3 HV.The mechanical properties of the samples reach the best value when the Y element content is 2 wt.%,the tensile strength at room temperature,700℃,and 800℃are 591 MPa,618 MPa,and 599 MPa,and the elongation are 3.8%,7.1%,and 10.7%.Compared with the sample without the Y element,the tensile strength increased by 29.6%,32.6%,and 63.7%,and the elongation at high-temperature increased by 77.5%and 114%.The tensile fracture of samples with different Y content at room temperature and high-temperature are quasi-cleavage fracture characteristics.The addition of Mo can effectively refine the grain size of Ti-48Al-2Cr-2Nb alloy.Because Mo is aβphase stable element,the addition of Mo can promote the transformation ofβ/B2 phase,andβ/B2 phase hinders the grain growth,thus refining the grain size.The amount of precipitates in the alloy increases with Mo content,and the morphology changes gradually.When the Mo content reaches 10 wt.%,the microstructure is connected to a network,and the hardness reaches the maximum about 425 HV.The mechanical properties of the samples reached the best value when the Mo element content is 8 wt.%.The tensile strength of the samples at room temperature,700℃,and 800℃were 576 MPa,608 MPa,and 580 MPa,and the elongation were 3.2%,4.4%,and 6.7%.Compared with the samples without the Mo element,the tensile strength increased by 26.3%,30.5%,and 58.5%,and the elongation at high-temperature increased by 10%and 34%.The tensile fracture characteristics of samples with different Mo content at room temperature and high-temperature are quasi-cleavage fracture characteristics.