Double-temperature model: a novel heating process for transient liquid phase bonding

摘要

A novel heating process, double temperature model, has been proposed for transient liquid phase (TLP) bonding to produce a homogenous joint with microstructure and properties that are similar to those of base metal. In contrast to conventional TLP bonding which maintains a temperature during bonding, this novel heating process relies on a higher temperature for a short time (a few seconds) and a lower temperature for a long time (a few minutes). Owing to a fall of temperature, a super-cooling of composition is formed at the solid/liquid interface and the equilibrium solidification is broken. Therefore a seamless joint without an interface is produced rather than a planar interface in the conventional TLP bonding. The limit of the interface on bond strength is removed, and the joint properties are improved. The double temperature model was verified experimentally for the bonding of T91 steel and 20-carbon steel respectively using an iron-base interlayer. Although the joint microstructure resembled that of T91 steel and 20-carbon steel base metals, a planar interface was observed in the conventional TLP bonding joint and no interface was found in the joint by double temperature model. Mechanical tests showed that double temperature model leaded to higher bond ductility for the T91 steel joint and higher impact toughness for the 20-carbon steel, which were equivalent to the base metal.