Achieving balanced enhancement of mechanical performance and heat resistance in Cf/SiC-superalloy joints by regulating active element Ti in brazing filler

Abstract

The application of Cf/SiC-superalloy joints in aerospace typically demands high strength and good heat resistance. However, the simultaneous improvement of the two properties is a pressing problem that needs to be addressed. This paper proposes the addition of diamond (C) powder to the Cu-Ni-Ti brazing filler to regulate the interface reaction between the filler and Cf/SiC composite and the initial liquefaction temperature of the interlayer, thereby achieving a balanced enhancement in both the mechanical performance and high-temperature resistance of the Cf/SiC-GH3044 joints. The results indicate that during the joining process, a brittle compound layer composed of TiC, Ti5Si3, and Ni16Ti6Si7 is formed at the Cf/SiC/interlayer interface. The thickness of the compound layer increases with elevated joining temperatures or prolonged holding times, which is detrimental to the strength of the joint. The added C particles react with the active element Ti to synthesize in situ some TiC reinforcing particles with the low thermal expansion coefficient in the interlayer. This not only suppresses the excessive growth of the brittle compound layer but also alleviates the residual thermal stress in the joint. Additionally, since Ti is a lowering-melting element in the Cu-Ni-Ti filler, the consumption of Ti by the C/Ti reaction raises the initial liquefaction temperature of the interlayer, thus improving the heat resistance of the joint. When the joining temperature and holding time were kept constant, the shear strength of the joint reached a maximum value as the C particle content increased. If the joining temperature was elevated or the holding time was extended, the C content associated with the peak strength also increased. By optimizing the C particle content, both the shear strength and heat resistance of the joint were improved. The maximum shear strength of the joint at room temperature and 900 °C were measured to be 245 MPa and 138 MPa, respectively. Moreover, the joint exhibited a maximum temperature capability of 1064 °C.