HVAF Combustion Cold Spray for Dense Metal Coatings
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Solution Overview
Problem
Conventional methods for producing bonded metallic coatings, such as cladding and cold spray, are costly and limited in achieving high-quality deposits with high-temperature metals, and often result in oxidized coatings that are brittle and prone to corrosion.
Innovation Solution
A high-velocity-air-fuel (HVAF) gun apparatus and method that uses a combustion chamber with a permeable burner block and liquid injection to create a high-velocity combustion gas stream, allowing for the deposition of fine-grained, dense metal coatings with reduced oxygen content by maintaining feedstock particles below their melting point during spraying.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cladding processes are used to produce bonded metallic coatings, then bonded attachment interface is achieved, but the process is time-consuming and requires substantial heat input
Solution Approach 1:
The invention changes the thermal parameters by using cold spray technology that maintains particle temperature below melting point, eliminating the need for substantial heat input and reducing process time while still achieving bonded interfaces through high-velocity impact bonding
Solution Approach 2:
The invention replaces the thermal-mechanical cladding process with a purely mechanical cold spray process that uses high-velocity particle impact to create bonded coatings without melting, significantly reducing heat input and process time
2Strength
If cold spray technology is used to deposit copper coatings, then sufficient bonding is achieved, but higher temperature materials require higher velocities that conventional devices cannot provide
Solution Approach 1:
The invention changes the gas temperature parameter to higher levels (above melting point of feedstock) while maintaining particle temperature below melting point through controlled heating, enabling conventional velocities to achieve sufficient bonding for high-temperature materials
3Temperature
If combustion thermal spray is used to produce metallic coatings, then high gas temperatures above melting point are achieved, but the sprayed metal powder is susceptible to oxidation
Solution Approach 1:
The invention uses an inert or reducing atmosphere in the combustion thermal spray process to prevent oxidation of the metal powder while maintaining high gas temperatures, eliminating the harmful oxidation effect
Solution Approach 2:
The invention converts the high temperature combustion process, which normally causes oxidation, into a beneficial process by controlling the atmosphere to prevent oxidation, allowing the high temperature to melt and bond particles effectively without the harmful side effect
4Manufacturing precision
If cold spray equipment uses higher gas temperatures for higher melting point metals, then better particle consolidation is achieved, but the process approaches the limitations of conventional thermal spray
Solution Approach 1:
The invention optimizes the gas temperature parameter to a specific range that provides sufficient heating for particle consolidation without reaching the extremes of conventional thermal spray, achieving better consolidation with a refined, controlled process
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 method produces cost-effective, high-quality metal coatings with low oxygen levels and improved mechanical strength, suitable for high-temperature metals, without the need for additional annealing steps, and is capable of using finer particles than conventional thermal spray processes.
Implementation Method 1
uses a combustion process to produce gas temperatures above the melting point of the particles and gas pressures to impart velocity to the particles
Implementation Method 2
gas pressures to impart velocity to the particles
Implementation Method 3
the temperature of the gas and particles is maintained at a sufficiently low temperature to prevent melting of the particles
Data Source
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AI summary
Different types of apparatus (10, 50) for fabricating a deposit (12, 86), method of deposition and an article (80) are presented. The apparatus (10) include a thermal spray gun (16) comprising a combustion chamber (22), combustion zone (28), an air injection port (18), a fuel injection port (20), a nozzle (30) and a liquid injection port (34). The combustion zone (28) exists between the inlet side (24) and outlet side (26) of the combustion chamber (22). The method includes, among other things, providing a fuel and an oxidizer inside the combustion zone (28), initiating combustion inside the combustion zone (28), and directing products of the combustion toward the outlet side (26) to create a combustion product stream. The method also includes introducing a feedstock mixture comprising a feedstock material and a liquid into the combustion product stream to create an entrained feedstock stream, and expelling the entrained feedstock stream from the spray gun through a nozzle to form a deposit on a surface of the article.