Microstructures and Properties of Transient Liquid Phase Bonding Joint of Single Crystal Alloy
Currently, single crystal superalloys have been widely used for turbine blades and nozzles in aero engine and industrial power plant. Joining technologies become more and more essential during manufacturing those complicated components, among which Transient Liquid Phase (TLP) bonding has the most potential because of its high compatibility in terms of microstructures and properties with base alloy. However, experiences have shown that excellent joining between single crystal alloy samples can be attained only on the basis of precise mating of grain growing direction, such as <001>, with angular deviation strictly controlled to be lower than 15°. Otherwise the mechanical properties of joints decrease significantly even after they are heat-treated using the same braze alloy and process parameters.
It has seriously restricted joining of single crystal alloys and affected the reliability of brazed components. However, it is still unclear which microstructural change has happened in the joint during TLP bonding of single crystal alloy and how it affects the mechanical properties of samples. The answers to these questions are very important for manufacturing and repairing of single crystal components
The research project involves TLP bonding of single crystal superalloy, especially focussing on the microstructures and properties of TLP-bonded joints. The main aim is to grasp the microstructural formation mechanism of TLP-bonded single crystal alloy joints and understand its effect to mechanical properties of joints. The microstructural characterisation in the solidified zone and the diffusion zone of the joints will be understood, including γ’ precipitation and sub-boundary formation. The micro and macro mechanical behaviours of joints will be evaluated, such as micro hardness of phases in the joints, micro crack initiation and propagation. Finally, the relationship between the microstructures and properties of TLP-bonded joints will be identified.
Dr Sheng Zhang