Effect of the isothermal solidification completion on the mechanical properties of Inconel 625 transient liquid phase bond by changing bonding temperature

Abstract

Transient liquid phase (TLP) bonding as an effective and precise bonding process attracted enormous attentions. However, there are several parameters affecting the mechanical properties of the joint zone which are crucial to be studied. In this work, two pieces of Inconel 625 alloy was bonded via TLP process using a BNi-2 interlayer. TLP process was done in different bonding temperatures (e.g., 1025 °C, 1100 °C, and 1175 °C) in a vacuum furnace in 10−5 bar pressure for 65 min. It is found that there is a meaningful relationship between process temperature and width of the eutectic phase zone. Results suggested that the rate of diffusion of melting point depressant atoms was increased by increasing the process temperature, leading to increasing the width of isothermal solidification zone (ISZ). It is found that the silicon and boron-rich eutectic compounds are responsible for large hardness value and weak the shear strength. To inhibit the formation of these hard and brittle phases, and to complete the ISZ region, the samples were bonded at 1175 °C and as a result, the ISZ region could be completed and mechanical properties were improved (e.g., the maximum shear strength at 1175 °C was measured to be 55.43% and 138.39% higher than 1100 °C and 1025 °C respectively). In addition to it, fracture cross-section was containing semi-cleavage and dimple shaped features which verified the completion of ISZ.

Keywords

• Inconel 625
• BNi-2
• Diffusion
• Transient liquid phase
• Isothermal solidification
• Melting point depressant