Ductile-Phase Toughening of Brazed Joints

Abstract

A heat treatment is presented that uses ductile-phase toughening to mitigate the effect of brittle intermetallics in a Ni-based braze alloy. The fracture resistance has been enhanced by creating a microstructure containing elongated ductile c-(Ni) domains that align, preferentially, across the joint. The development of this beneficial microstructure is based on an understanding of the transient dissolution, isothermal solidification, and coarsening phenomena. Due to slow kinetics, the elimination of intermetallics by diffusion is avoided in favor of ductile domain formation through solidification control. The toughening has been attributed to a combination of bridging and process zone dissipation, enabled by the ductile phase.

Microstructural evolution mechanism during brazing of Hastelloy X superalloy using Ni–Si–B filler metal

“…Two approaches can be followed: This heat treatment can be conducted at a temperature higher than ternary eutectic temperature of Ni-Si-B, where there is sufficient liquid to facilitate rapid coarsening, and lower than re-melting temperature of the primary γ phase. This approach has been previously applied by Philips et al [19] for toughening the AISI304/Ni-Cr-Si-P/AISI304 brazed joint to mitigate the effect of brittle IMCs in the brazed alloys.…”

“…To avert brittleness, it is a needed to design a proper thermal treatment to modify the joint microstructure. Generating a beneficial microstructure and enhancing the robustness of brazed joints rely on a detailed understating of the microstructural evolution during the bonding process [18, 19]. Therefore, a fundamental knowledge of the metallurgical transformations during brazing is required to achieve sound, strong and reliable joints.…”

Intermetallic phase formation during brazing of a nickel alloy using a Ni–Cr–Si–Fe–B quinary filler alloy

“…Therefore, the identification of nature and amount of the intermetallic compounds formed during brazing are necessary for effective structural designs involving brazing for these applications. Moreover, enhancing the robustness of the brazed joints via applying a post-braze heat treatment rely on a detailed understating of the microstructural evolution during the bonding process [4,26]. There are some theoretical and experimental research studies on the solidification behaviour of ternary braze alloys such as Ni-Cr-B alloys [6,27,28] and Ni-Si-B alloys [7,[29][30][31][32].…”

“…Therefore, the identification of nature and amount of the intermetallic compounds formed during brazing are necessary for effective structural designs involving brazing for these applications. Moreover, enhancing the robustness of the brazed joints via applying a post-braze heat treatment rely on a detailed understating of the microstructural evolution during the bonding process [4, 26].…”

Characterization on Fracture Surfaces of 304 Stainless Steels Joined by Brazing Using Silicon Nanoparticles

“…Therefore, the filler metals containing silicon and boron decrease the melting point and reduce the eutectic structures [5,6]. Moreover, the presence of the TLP, rich in silicon and boron, prevents damage to the weld bead [7,8]. The objective of this work is the to study the formation of transient liquid phases on fractures of 304 stainless steel, to promoting the following: a) forming a liquid capable of increasing the wettability between microcracks and internal micropores, b) improving capillary forces between the filler metals and the transient liquid phase and c) modifying the phase formation.…”