Interfacial microstructure and mechanical properties of GH99 superalloy and Nb brazed joint using Cu75Pt25 filler

Abstract Cu75Pt25 brazing filler was applied to brazing GH99 superalloy to Nb, and the sound joints were obtained by adjusting brazing parameters. The typical interfacial microstructure of the brazed joint was Nb/Nb7Ni6+NbNi3/ Ni(s,s)+Cr-rich NbNi3+(NbCr2+NbNi3)/GH99. The effects of brazing temperature and holding time on the interfacial microstructure of GH99/Cu75Pt25/Nb joints were studied. The results showed that the solution and diffusion of Ni atoms from GH99 substrate into brazing seam played a critical role in the interfacial microstructure evolution. As the brazing temperature rose, the Nb–Ni reaction layer was formed instead of the initial Nb3Pt layer, and the thickness increased firstly and then remained constant. The highest shear strength of the joint reached 152 MPa when brazed at 1150 °C for 15 min. All of the joints presented a brittle fracture mode during shear test, and the fracture location changed from Nb3Pt layer to Nb–Ni compounds layer.