Effects of cooling rate and holding time on microstructure and property of TLP bonded joints for DD3 single crystal superalloy

Transient liquid phase (TLP) bonding of DD3 single crystal superalloy at 1250℃ with different holding time was studied. Two cooling methods such as furnace-cooling (FC) and Ar-quench cooling (AC) were adopted. An aging treatment with 870℃/32h/air cooling was performed after the welding process. Microstructures of bonding seams and base metals with different welding conditions were observed and stress-rupture properties at 980℃ of the joints were tested. The results show that the size of γ'phases of bonding seams and base metals by FC increases with holding time, and the shape becomes irregular. While when AC method is used, the size and shape of γ'phases are not changed with holding time and γ'phases are still fine and cube-like. Low cooling rate makes γ'phases of welding seams and base metals become bigger, which leads to the deterioration of mechanical properties of the joints and base metals. On the other hand, high cooling rate makes fine and cube-like γ'phases, which increases the mechanical property of the joints, and ensures the property of the base metal is maintained.