Microstructural evolution and growth kinetics of interfacial compounds in TiAl/Ti3SiC2 diffusion bonding joints

Abstract

TiAl intermetallic was direct diffusion bonded to Ti3SiC2 at 900 °C, 950 °C, and 1000 °C with a holding time ranging from 0.25 h to 64 h. The interfacial microstructural evolution, the growth kinetics and the mechanical properties of the bonded TiAl/Ti3SiC2 joints were systematically investigated. The build-up of interfacial compounds in the TiAl/Ti3SiC2 joints changed from γ+α2/γ/Ti5Si3/Ti3SiC2 to γ+α2/γ/TiAl2/Ti5Si3/Ti3SiC2, to γ+α2/γ/TiAl2/Ti5Si4/Ti5Si3/Ti3SiC2, and to γ+α2/γ/TiAl2/TiAl3+Ti5Si3/Ti5Si4/Ti5Si3/Ti3SiC2 as the holding time or bonding temperature increased. The formation sequence of interfacial phase at the joint was: Ti5Si3→Ti5Si4→TiAl2→TiAl3. The de-intercalation Si atoms from the Ti3SiC2 diffusing into the TiAl base alloy and reacting with the Ti was responsible for the formation of the interfacial reaction layers. The thicknesses of the interfacial reaction layers grew following the parabolic kinetic law, indicated their growth was controlled by the bulk diffusion. The bonding activation energy was 213 kJ/mol. The joint, bonded at 900 °C for 9 h, had the highest shear strength (about 53 MPa) with a γ+α2/γ/TiAl2/Ti5Si4/Ti5Si3/Ti3SiC2 interfacial microstructure and with a total thickness of 6 μm.