Search

The two-phase microstructural evolution and the remained fractions of γ′ were investigated by scanning electron microscope (SEM) for a series of γ′-richen single crystal superalloys from the IC alloys system. At alloys IC31 and IC32, high levels of the dissolution of γ′ cause the remarkable damages of two-phase microstructure, especially when the fraction drops to less than 45%, the γ′ phase becomes sphere significantly and the two-phase interface distorts fairly. And the relationship between different degrading stages and the remained fractions are discussed systemically. The dissolution temperatures, Tsol, of IC alloys determined by differential scanning calorimetry (DSC) are further considered. It is found that there is a good linear relationship between the Tsol and the remained fraction of the γ′ at 1200°C and the slide keeps fixed as about 0·5%/°C. Meanwhile, the remained fraction of the γ′ seems to play an important role on the mechanical properties, and a method with Tsol used to estimate the properties at 1200°C is proposed. [ABSTRACT FROM AUTHOR]

Nickel based single crystal superalloy DD5 was brazed with the AWS classification filler metal BNi-2 at brazing temperature of 1323-1423 K for holding 10-240 min. The effect of the brazing temperature and brazing time on the microstructure of the brazed joint was investigated by scanning electron microscope (SEM) and electron probe microanalyser (EPMA). The result indicates that the joints exhibit sound bonding without any defect and crack. Three distinct regions can be identified in the joint: a diffusion affect zone composed of γ-γ′ phase and fine M3B2 precipitates, an interfacial bonding zone solidified isothermally at the brazing temperature, and braze alloy zone formed by the solidification of surplus molten filler alloy during cooling. The braze alloy zone consists of γ+γ′ eutectic phase, chromium boride, and ternary eutectic phase of γ-nickel, nickel boride and nickel silicide. With extending brazing time, the thickness of interfacial bonding zone and diffusion affect zone increased while brittle compounds reduced. The bonding mechanism was discussed with reference to the microstructure evolution of the joint. [ABSTRACT FROM AUTHOR]