Interfacial microstructure evolution and mechanical characterization of brazed Al2O3 joints with Ni‒Ti interlayer: An experimental and theoretical approach

Reliable brazing joints of Al₂O₃ ceramics were obtained using an active Ni‒Ti interlayer under vacuum conditions. The interfacial microstructure and mechanical properties of the joints were studied. The structural, electronic, and elastic properties of the primary interfacial reaction phases were determined using first–principles calculations. After brazing at 1320 °C for 30 min, Ni₂Ti₄O layer and columnar AlNi₂Ti formed at the interface adjacent to the Al₂O₃ substrate. With increasing brazing temperature between 1300 °C and 1380 °C, Ni₂Ti₄O layer thickened gradually, and the AlNi₂Ti became increasingly longer. As brazing temperature reached 1400 °C, TiO was formed at the interface, and the Ni₂Ti₄O content decreased significantly; moreover, bulk AlNi₂Ti and TiNi₃ were distributed in the brazing seam. The highest shear strength of 129 MPa was achieved when brazed at 1350 °C for 30 min. According to the first–principles calculations, Ni₂Ti₄O is more readily formed than AlNi₂Ti, whereas AlNi₂Ti exhibits greater stability than Ni₂Ti₄O. Both AlNi₂Ti and Ni₂Ti₄O possess metallic bonds, contributing to the adhesion of the filler metal to the Al₂O₃ substrates. The calculated modulus and Poisson’s ratio indicate that both AlNi₂Ti and Ni₂Ti₄O exhibit ductile characteristics, which assist in relieving residual stress within the joint.