Diffusion bonding behaviour of Nb–Si and TiAl alloys by spark plasma sintering

Abstract

Nb–Si alloy and high niobium β-γ TiAl alloy(HNBG) was joined by diffusion bonding ranging from 1000 to 1100 °C at 10 MPa for 20 min by spark plasma sintering. The phase sequence from HNBG to Nb–Si side was HNBG||β/B2+α2-Ti3Al||δ-(Nb, Ti)3Al+σ-(Nb, Ti)2Al + Ti rich γ-(Nb, Ti)5Si3||Nb–Si in the joint. The sound joints without any pores were obtained with the bonding temperature above 1050 °C. The nano-indentation test results showed that Ti rich γ-(Nb, Ti)5Si3 and σ-(Nb, Ti)2Al phases had relatively high hardness and elastic modulus in the diffusion zones II. The highest shear strength of 269 MPa was achieved at 1050 °C. Fracture mainly occurred along the interface of the diffusion zones due to low interfacial adhesion induced by lower bonding temperature. As the bonding temperature was higher, the cracks propagated mainly from in the interface to through the phases due to the increase of interfacial adhesion. The joining mechanism of HNBG/Nb–Si joint was analysed through diagram.

Keywords

• Nb-Si alloy
• TiAl alloy
• Diffusion bonding
• Microstructure evolution
• Mechanical properties