Study On Microstructure Evolution And Deformation Behavior Of Fe Based Alloy Co-Strengthened With B2 Phase And L2₁ Phase

Because of the advantages of low cost and high strength,B2 phase reinforced iron-based alloys play an important role in energy,transportation,aerospace and other fields.At present,it has attracted extensive attention of researchers by adding Ti element to B2 phase reinforced iron-based alloys to form L2₁ phase to improve the plasticity and creep resistance of the alloy at room temperature.However,the understanding of microstructure evolution and deformation behavior of B2 phase and L2₁ phase co-strengthing iron-based alloys is not comprehensive enough and needs to be studied further.In this paper,Fe-32（Ni+Co+Al+Ti）-10Cr-2Mo（wt.%）alloy reinforced with B2 phase and L2₁ phase are studied.The microstructure evolution of the alloy matrix and precipitated phase during heat treatment and the deformation behavior of the alloy at room temperature tensile condition are studied,and the theoretical analysis and discussion are carried out in order to lay a theoretical foundation for the further development of multiphase co-strengthing iron-based alloys.The test results show that the aged alloy matrix is composed of ferrite and austenite,and the precipitated phases in the matrix consist of B2-（Ni,CO）Al phase and L2₁-Ni₂TiAl phase.The precipitated phases in different matrices show different shapes.The precipitated phases in ferrite matrix are spherical,while the precipitated phases in austenite matrix are rod-like.L2₁-Ni₂TiAl phase is formed at the interface and in the interior of the larger B2 phase,which is related to the heterogeneous nucleation at the interface and the further ordering of B2 phase structure.In the aging process,the coarsening behavior of spherical precipitated phase in ferrite matrix follows LSW theory.With the increase of aging temperature,the coarsening rate of precipitated phase increases.But the coarsening rate of precipitated phase decreases with the prolongation of aging time.After aging treatment at 550℃/2h,part of austenite in the matrix is transformed into ferrite.In addition,after aging treatment,the number of large angle grain boundaries in the alloy increases.After rolling treatment,a high-density dislocation distribution region is formed inside grains and at grain boundaries of the alloy.In the process of plastic deformation,this region can interact with dislocations to improve the strength of the alloy.Compared with the solid solution alloy（850℃/1h）,the strength of the aged alloy（850℃/1h+550℃/2h）increases greatly,while the elongation decreases by nearly 50%.The strain hardening index of solid solution alloy and aged alloy are 0.54 and 0.37respectively,which indicates that the ability of solid solution alloy has better resistance to uniform plastic deformation.During the tensile process at room temperature,when the plastic deformation of the alloy is small,a flat slip line is formed in the austenite matrix.The slip line continues to expand in austenite and is hindered when it extends to the interface between austenite and ferrite,but no slip line is found in austenite matrix.With the continuous plastic deformation,the number of slip bands in austenite matrix increases significantly and forms a slip band network,and slip lines also sprout in ferrite matrix.