An efficient method to engage oxide ceramics in low-temperature interfacial reactions: Microstructure evolution and kinetics behaviors based on supercooling in a transient liquid phase bonding joint

Abstract

Ductile transient liquid phase (TLP) bonding joints reinforced by multiple precipitates were produced using novel pre-sintered coatings and Au-Si fillers; therefore, the highest strength of NiTi/sapphire joints brazed at 460 °C for 30 min reached 72 MPa. The pre-sintering process improved the surface-active of sapphire by forming metastable Ti3O and non-stoichiometric Al2O3. The typical brazing seam consisted of O-rich compounds, TiSi2, and Ti-Ni-Si, wherein the O-rich phase featured different crystallinity depending on the oxygen content. The sapphire/seam interface was either a nanoscale diffusion region or a Si-rich amorphous layer. The breakdown of the Stokes-Einstein relation (SER) occurred, and the deviation from SER increased with a higher cooling rate. The influence of coating thickness was reflected in (i) the supercooling related to the viscosity and fractional exponent of liquids and (ii) the microstructural change of the joint related to the driving force for crystal growth. This work presented a new strategy for joining ceramics to metals at lower temperatures but using the joint at higher temperatures; furthermore, gave an insight into the microstructure evolution and kinetics behaviors based on supercooling in a transient liquid phase bonding joint.