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

A model of dissolution and isothermal solidification during the transient l iquid phase (TLP) bonding process of nickel using Ni-15.2wt.% Cr-4.0wt.% B ternary filler metal is presented. The model combined thermodynamic calcula tion with Thermo-Gale software and diffusion analysis by a finite differenc e method. The model assumed diffusion-controlled transformation, and the eq uilibrium compositions at the solid-liquid interface were calculated using Thermo-Gale software. The interface velocity was determined from the mass b alance of solutes diffusing into or out from the interface. When a Ni speci men with a 30 mu m thick filler metal was kept at 1473 K for 3.6 ks, isothe rmal solidification was almost complete. On the other hand, when the specim en was kept at 1373 K for 3.6 ks, residual liquid remained in the bonding r egion. The solidification sequence of the residual liquid during the coolin g 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 reg ion concurred with the experimental result.