Microstructure Evolution and Shear Strength of TiAl‐Based Intermetallics Joint Vacuum Brazed with TiH2–Ni–TiB2 Powder Filler

Abstract

Vacuum brazing of Ti–47Al–2Nb–2Cr–0.15B (at%) alloy with TiH2–Ni–TiB2 powder filler in situ assisted 20 vol% TiB whiskers is performed at 1190–1250 °C for 10 min. The microstructure evolution of the joint at various brazing temperatures and the relationship between microstructure and joint properties are systematically investigated. In the results, it is indicated that the interfacial microstructure of the γ‐TiAl joint brazed at 1230 °C is γ‐TiAl/Ti3Al + Al3NiTi2 (layer I)/Al3NiTi2 + Ti3Al (layer II)/Al3NiTi2 + TiB + Ti3Al (layer III)/Al3NiTi2 + Ti3Al (layer II)/Ti3Al + Al3NiTi2 (layer I)/γ‐TiAl. The layer II containing high‐hardness Al3NiTi2 is always the weakest part in the brazed joint. The microstructure refinement and load‐bearing behavior of layer III are increased with brazing temperature due to the increasing length of the TiB whisker. Variation of the content of low‐hardness Ti3Al in layer II as well as its microstructure refinement and internal bonding strength, the shear strength of γ‐TiAl joints is first increased and then decreased with brazing temperature, but that of Al3NiTi2 in layer II is reversed. The joint brazed at 1230 °C possesses the maximum shear strength of 332.87 MPa and a quasi‐cleavage fracture occurs in the layer II mainly consisted of Al3NiTi2.