Investigation on microstructure and mechanical properties of a vacuum brazed joint of γ′-strengthened Co-based single crystal superalloy before and after the post-bond heat treatment. (July 2020)

• Record Type: Journal Article
• Authors: Wang, S.Y.; Sun, Y.; Hou, X.Y.; Cui, C.Y.; Sun, X.F.; Zhou, Y.Z.
• Is Part Of: Vacuum. Volume 177(2020)
• Publication Date: 2020-07
• Subjects: Transient liquid phase bonding -- γ′-strengthened Co-Based single crystal superalloy -- Microstructure -- Microhardness; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2020.109413
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: Transient liquid phase bonding of γ′-strengthened Co-based superalloy was carried out using Ni-based filler alloy. The effects of post-bond heat treatment (PBHT) on the microstructure and mechanical properties of the γ′-strengthened Co-based superalloy joint were systematically investigated. Two distinct regions were observed in the isothermally solidified zone: primary γ′ phase zone (PZ) and secondary γ′ phase zone (SZ). The diffusion of Al from the substrate to the liquid interlayer proves to be the main reason for the precipitation of γ′ phases, showing a significant growth trend after the PBHT. The joint after the PBHT shows higher microhardness in most areas of the bonding zone. However, some parts of the diffusion affected zone show the contrary result. This could attribute to the competition consequence of the solid solution strengthening and second phase strengthening. Furthermore, the post-bond heat treated joint exhibited higher yield strength and longer stress rupture life. Our experimental results help to better understand the microstructural characteristic of the new type Co-based superalloy and provide a direction for further optimizing the brazing joint. Highlights: Two kinds of γ′ phases constituting two regions were found in the ISZ. Rafting γ′ microstructure was formed in the DAZ after post-bond heat treatment. Precipitation of secondary-γ′ phases in the joint after post-bond heat treatment plays a key role in strengthening the joint. Both tensile and stress rupture properties improved after the post-bond heat treatment.