Synthesis of Ti_xZr_yNbNi multi-principal element amorphous and amorphous/nanocrystalline filler metals and their effects on microstructure and mechanical properties of Ti₂AlNb brazed joints

Multi-principal element alloys (MPEAs) ribbons with amorphous structure are attractive for the potential application as novel brazing filler metals (BFMs). In this work, amorphous and amorphous/nanocrystalline Ti_xZr_yNbNi (x = 1, 1.5, 2; y = 1, 1.5, 2, in molar ratio) MPEA ribbons were designed and prepared by melt-spinning and used as BFMs to join Ti₂AlNb alloy. The critical thickness for glass formation of the equimolar TiZrNbNi alloy was 50 μm, and decreased to 20 μm with the increase in Ti or Zr content. The better glass-forming ability (GFA) of TiZrNbNi alloy was mainly attributed to its lower crystallization driving force upon cooling and higher thermal stability of supercooled liquid. The Ti₂AlNb joints brazed with Ti_xZr_yNbNi BFMs at 1273 K for 20 min exhibited multi-layer microstructure mainly consisting of β-(Ti, Nb)+Laves phases in the center region of braze zone and B2 +O phases adjacent to the base metal. The simulation results of phase formation using software Pandat 2024 indicated that the β-(Ti, Nb) formed first during brazing, followed by the precipitation of Laves phase from residual liquid phase upon cooling. Compared with the joints brazed with the high Ti or Zr content BFMs, the Ti₂AlNb/TiZrNbNi/Ti₂AlNb joint exhibited higher amount of β-(Ti, Nb) phase and lower amount of Laves phase with uniform distribution, leading to the superior compressive shear strength of 261 MPa at room temperature and 240 MPa at 923 K. These findings indicate that the novel TiZrNbNi MPEA ribbon is a promising BFM for high-strength joining of Ti₂AlNb alloy.