Numerical modeling of the transient liquid phase bonding process of Ni using Ni-B-Cr ternary filler metal

Abstract

A model of dissolution and isothermal solidification during the transient liquid phase (TLP) bonding process of nickel using Ni-15.2wt.%Cr-4.0wt.%B ternary filler metal is presented. The model combined thermodynamic calculation with Thermo-Calc software and diffusion analysis by a finite difference method. The model assumed diffusion-controlled transformation, and the equilibrium compositions at the solid-liquid interface were calculated using Thermo-Calc software. The interface velocity was determined from the mass balance of solutes diffusing into or out from the interface. When a Ni specimen with a 30 µm thick filler metal was kept at 1473 K for 3.6 ks, isothermal solidification was almost complete. On the other hand, when the specimen was kept at 1373 K for 3.6 ks, residual liquid remained in the bonding region. The solidification sequence of the residual liquid during the cooling stage was calculated by the Scheil simulation. The simulation showed that solidification of the residual liquid is completed with a ternary eutectic reaction, L→fcc+Ni₃B+CrB. The calculated width of the eutectic region concurred with the experimental result.