Effects of Recrystallization on Interfacial Microstructure Evolution and Shear Properties Strengthening Of Tial Alloy Joints

Abstract

The effects of dynamic recrystallization(DRX) and post bonding heat treatment(PBHT) on the interfacial microstructure evolution and mechanical properties promotion of Ti-43Al-4Nb-1Mo-0.2B alloy joints with different bonding parameters were investigated by microstructural characterization and shear performance tests. Interfacial microstructure with a strip-like DRX area was obtained when bonding at 1100 ℃-30 MPa-60 min. Equiaxial γ grains at the interface undergo discontinuous dynamic recrystallization during bonding process, and tend to form flat grains parallel to lamellae direction during recrystallization annealing treatment(1000 ℃/6 h) owing to the obstruction of the lamellae on both sides. The variation of the angle between lamellae orientation and stress axis direction affects the stress distribution and lamellae deformation at bonding interface, which in turn affects the DRX behavior and the width of DRX aera. The static recrystallization behavior during recrystallization annealing treatment can be utilized to eliminate welded defects of joints bonding at lower pressure or temperature. Bonding joints with flawless interfacial microstructure and excellent shear properties can be obtained after single-α phase annealing treatment, leading to the DB interface shutting and transferring into full lamellae. Lamellae microstructure tailored through PBHT can promote the shear strength of joints due to the crack deflection from along interface to the inner of the matrix during shear process. The highest strength of 478 MPa can be obtained under the parameters of 1100 ℃/30 MPa/60 min-1290 ℃/15 min, reaching 82% of the matrix strength. This work provides important DB process parameters for manufacturing complex structural parts of TiAl alloy.

Keywords: TiAl alloy, Diffusion bonding, Heat treatment, Dynamic recrystallization