ALD Oxide Coating for Active Braze Runout Control
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Solution Overview
Problem
Active brazing often results in excessive flow of braze filler metal due to chemical reactions at the faying surfaces, leading to runout and impaired hermeticity and mechanical strength of the brazed joint, with existing methods like stop-off materials being ineffective or requiring post-braze cleaning.
Innovation Solution
Applying a thin conformal metal oxide coating, preferably using atomic-layer deposition (ALD), to the metal faying surface to balance surface energies and prevent excessive braze filler metal flow during active brazing, while maintaining joint integrity and not hindering subsequent processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If active brazing is performed without barrier coating, then good wetting and bonding is achieved, but excessive braze filler metal flow and runout occurs
Solution Approach 1:
A thin metal oxide barrier layer is deposited on the metal faying surface to act as an intermediary between the active brazing filler metal and the metal substrate. This barrier layer prevents direct chemical reactions that cause excessive flow while still allowing adequate wetting and bonding, thus resolving the contradiction between good bonding and runout control
Solution Approach 2:
The surface energy of the metal faying surface is modified by depositing a metal oxide barrier layer, changing the chemical composition and surface properties. This parameter change allows control over the spreading behavior of the liquid brazing filler metal, preventing runout while maintaining bonding
2Manufacturing precision
If stop-off materials are used to prevent braze filler metal flow, then runout is reduced, but post-braze cleaning is required
Solution Approach 1:
Instead of using disposable stop-off materials that require cleaning, a thin metal oxide barrier layer is deposited that becomes part of the joint structure. This barrier layer serves its function during brazing and remains as a harmless residue that does not require removal, eliminating the cleaning step
Solution Approach 2:
The metal oxide barrier layer acts as a permanent intermediary that prevents excessive flow without requiring removal. Unlike temporary stop-off materials, the barrier layer is designed to remain in the final assembly without interfering with joint performance, thus eliminating post-braze cleaning requirements
3Manufacturing precision
If peak brazing temperature and time are decreased to reduce runout, then braze filler metal flow is reduced, but joint strength and hermeticity are compromised
Solution Approach 1:
By changing the surface energy parameters through metal oxide barrier layer deposition, the spreading behavior of the brazing filler metal is controlled. This allows maintaining adequate wetting and joint strength at standard brazing temperatures and times while preventing excessive runout, avoiding the need to compromise joint quality
4Manufacturing precision
If joint geometry or surface roughness is modified to control runout, then braze filler metal flow is limited, but manufacturing complexity increases
Solution Approach 1:
Instead of modifying joint geometry or surface roughness through mechanical means, a thin metal oxide barrier layer is deposited using atomic layer deposition (ALD). This replaces complex mechanical joint preparation with a controlled deposition process that precisely controls runout without increasing overall manufacturing complexity
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 thin ALD coating effectively eliminates braze filler metal runout, ensuring hermetic seals and high mechanical strength without the need for post-braze cleaning or altering the base material properties, as demonstrated by reduced runout and maintained joint tensile strength in tests.
Implementation Method 1
applying a thin conformal coating of a metal oxide to the metal faying surface... The thin metal oxide coating is applied by atomic-layer deposition (ALD)
Implementation Method 2
When heated above the liquidus temperature, the liquid filler metal is normally contained within the brazement by capillary attraction
Implementation Method 3
The active element Zr will diffuse to the ceramic-braze filler metal interface and react with the alumina to reduce the local oxide, essentially replacing some Al atoms in the alumina with Zr to form the more stable zirconia
Implementation Method 4
atoms from the metal object faying surface can diffuse into the liquid braze alloy and vice versa at the metal-braze filler metal interface
Implementation Method 5
applying a thin conformal coating of a metal oxide to the metal faying surface to balance surface energies and prevent excessive braze filler metal flow
Data Source
AI summary
Nanometers thick conformal coatings deposited by atomic-layer deposition (ALD) onto the metal surface of an active braze joint modifies the surface chemistry to eliminate excess braze filler metal flow. Unlike other means used to prevent braze filler metal runout, the thin ALD coating does not hinder next assembly processes, does not require post-braze cleaning, and does not alter the base material mechanical properties.