Effective diffusion coefficient for Cu in steel joined by transient liquid phase bonding

Abstract

Seamless carbon steel tubes were joined by the transient liquid phase (TLP) bonding process using Cu foilsas interlayers. Bonding was performed at 1300 °C for 7 min with an applied uniaxial pressure of 5 MPa. Thecompletion of isothermal solidification was not systematically achieved along the joint, leading to the presenceof athermally solidified liquid (ASL). Consequently, the ability to predict the time to complete isothermalsolidification ? and therefore its kinetics ? is of great interest. For this purpose, a one-dimensional modelusing the finite element method was employed to simulate the TLP bonding. In particular, regions where thecompletion of the process was not achieved provided a source for the effective diffusion coefficient (Def) forthe bonding process. By knowing Def, different cases were considered within the proposed model, from theremaining time to complete the bonding process for an observed ASL, to the maximum liquid gap that can beisothermally solidified for a selected holding time. The validity of the utilization of Def was confirmed by analysingthe diffusion kinetic regime of Cu in steel.