Au-Cu-Ni Brazing Alloy for WC-Co to Titanium Joints
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Solution Overview
Problem
Conventional brazing alloys for tungsten carbide-cobalt (WC-Co) substrates to titanium or titanium alloys result in brittle braze interfaces, leading to cracking and wear issues, particularly in gas turbine engine applications where high ductility and impact resistance are needed.
Innovation Solution
A brazing material comprising 40 to 60% by weight gold, 5 to 16% by weight nickel, and 35 to 55% by weight copper is used to form a braze joint with a post-braze hardness of 450 to 600 KHN and improved impact resistance greater than 0.60 Joules, ensuring ductility and preventing substrate damage during the brazing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If titanium-copper-nickel (TiCuNi) alloy braze foils are used to braze WC-Co wear pads to titanium substrates, then the braze joint achieves high hardness (about 1200 KHN), but the braze interface becomes brittle and cracks at impact energies as low as 0.30 Joules
Solution Approach 1:
The patent changes the chemical composition parameters of the brazing alloy from conventional TiCuNi to a specific Au-Cu-Ni formulation (40-60 wt% Au, 35-55 wt% Cu, 5-16 wt% Ni). This parameter change fundamentally alters the metallurgical behavior during brazing, preventing the formation of brittle intermetallic compounds while maintaining adequate joint strength and hardness.
Solution Approach 2:
The invention creates a composite braze joint structure where the Au-Cu-Ni brazing alloy forms a ductile matrix that bonds the WC-Co wear pad to the titanium substrate. The composite nature of the brazing material itself (multi-element alloy) provides both strength and ductility, resolving the contradiction between hardness and toughness.
2Strength
If conventional brazing alloys are used to braze WC-Co substrates to titanium alloys, then the braze joint forms a hard interface, but the wear pad may be liberated from the substrate at impact energy of about 0.60 Joules
Solution Approach 1:
The patent modifies the brazing alloy composition parameters to include significant gold content (40-60 wt%) combined with copper and nickel in specific ratios. This parameter change results in a brazing material that produces softer, more ductile joints capable of absorbing impact energy through plastic deformation rather than brittle fracture, thereby improving impact resistance while maintaining adequate hardness.
3Strength
If high temperature braze is used to join wear pads to titanium blades, then the braze joint achieves sufficient strength, but titanium forms brittle compounds with the alloying elements of the wear pad in the braze joint
Solution Approach 1:
The Au-Cu-Ni brazing alloy acts as an intermediary material between the WC-Co wear pad and the titanium substrate. The specific composition of this intermediary layer prevents direct reactive bonding between titanium and the wear pad alloying elements, eliminating the formation of brittle intermetallic compounds while still providing strong metallurgical bonding to both substrates.
Solution Approach 2:
The patent changes the chemical composition parameters of the brazing alloy to gold-rich formulations with specific Cu and Ni content. This parameter change alters the thermodynamics and kinetics of the brazing process, preventing the formation of brittle titanium-alloying element intermetallics that occur with conventional TiCuNi alloys, while maintaining adequate bond strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The gold/nickel/copper brazing material enhances the impact resistance and ductility of the braze joint, preventing cracking and wear, and maintaining the mechanical properties of the substrates, even at high temperatures, thus addressing the limitations of existing alloys.
Implementation Method 1
Diffusion occurs between TiCuNi braze foil and WC—Co wear pad during high temperature braze.
Data Source
AI summary
A brazing assembly includes a tungsten/carbide/cobalt substrate (e.g., wear pad), a second substrate including titanium or titanium alloy (e.g., a midspan shroud of a fan or compressor blade) and a brazing material including gold, nickel, and copper present in respective amounts to improve the ductility of the braze joint. A brazed article includes a first substrate, a second substrate, and a braze joint having a post-braze hardness of between 450 and 600 KHN. A method to improve the impact resistance of a braze joint between a tungsten/carbide/cobalt substrate and a substrate including titanium or alloy thereof includes utilizing a brazing material including gold, nickel, and copper and brazing at temperatures less than about 1900° F. (1038° C.).