Effects of pressure on microstructure and properties of wide-gap brazed joints

SUN Yubo; YUAN Xiaoguang; WANG Zhiping

doi:10.7688/j.issn.1000-1646.2025.05.14

Abstract：[Objective]Cracks in aero-engine turbine guide vanes are typically repaired using wide-gap brazing.However,pores usually appear during the formation of wide-gap brazed joints,which can lead to a decline in their high-temperature mechanical properties.To suppress the formation of pores,a certain pressure is applied during brazing.Nevertheless,the effects of brazing pressure on the microstructure and mechanical properties of wide-gap brazed joints remain unclear.[Methods]In this study,wide-gap brazed joints were prepared under different brazing pressures.The effects of brazing pressure on the microstructure and mechanical properties of the joints were investigated through tensile testing,microhardness characterization,fracture morphology observation,energy dispersive spectroscopy(EDS)analysis,and X-ray diffraction(XRD).[Results]The experimental results show that at a constant brazing temperature,the tensile strengths of the wide-gap brazed joints under brazing pressures of 10,20,and 50 kg with the mass ratio of the brazing filler metal to the base metal as 40∶60 are 436.57,411.76,and 381.95 MPa,respectively,namely that the tensile strength of the joints decreases with increasing brazing pressure.Microhardness and EDS analysis of the joint fracture surface reveal that as the brazing pressure increases,the concentrations of melting point depressant elements and active elements at the fracture surface become higher,and the microhardness significantly increases.This indicates that higher brazing pressure leads to uneven microhardness distribution in the joint,inducing significant stress concentration and thereby reducing joint strength.XRD results confirm that the applied brazing pressure causes noticeable lattice distortion in the joint and base material.Higher brazing pressure results in greater lattice distortion,which blocks the diffusion channels of melting point depressant elements and active elements,hindering their diffusion.This leads to the accumulation of these elements in the joint and base material,thereby causing uneven microhardness distribution and a decline in joint strength.Post-welding heat treatment or increasing the brazing temperature can alleviate lattice distortion,enhance element diffusion,and improve the mechanical properties of the joint.[Conclusion]Applying a certain pressure during the preparation of wide-gap brazed joints helps suppress the formation of internal pores.However,the contradictory effects of brazing pressure and temperature on lattice distortion need to be carefully considered.Excessive brazing pressure can hinder element diffusion,while increasing the brazing temperature can enhance element diffusion,reduce the unevenness of microhardness distribution,and ultimately improve the mechanical properties of the joints.