The aerospace industry has high-dollar components that cause even higher-dollar down-time when they require maintenance, repair, or replacement. Aerospace maintenance has traditionally relied on thermal spray processes, like flame spraying and arc spraying. These modalities have been used since the early 1900s to repair and enhance original equipment.
Cold spray technology is a much more contemporary development, gaining traction in the 1990s. Portable, high-pressure, cold spray technology equipment, like that developed by VRC Metal Systems, is at the forefront of this emerging field.
Find out how Mid-America Aerotech can provide faster, market-competitive, and safer aerotech maintenance and repairs using advanced Cold Spray technology. Contact us and discover why more aerospace companies choose Mid-America Aerotech.
Cold Spray Technology
What Is Cold Spray?
Cold spray is an industrial coating deposition process in which powdered metal or other material accelerates to supersonic speeds, sometimes as high as Mach 3. The accelerated powder is deposited onto a substrate. The powders reach a high velocity using a high-pressure, electrically-heated carrier gas, like helium or nitrogen.
Once the metal particles achieve these high speeds and collide with the substrate, the particles undergo a plastic deformation which causes them to bond to the surface. The mechanical interlocking of the particles and recrystallization at the surface creates a strong bond between particle and surface.
There are two different types of cold spray:
High-pressure cold spray (HPCS) uses nitrogen, helium, or air at pressures ranging from 300-1000 psi and utilizes spraying high-strength metals and metal alloys.
Low-pressure cold spray (LPCS) uses the same compressed gases as the high-pressure cold spray but at pressures below 300 psi. LPCS involves spraying soft metals and mixtures of metals and ceramic powders.
Using Cold Spray
Cold spray powders can be pure metals, metal alloys, or be a mixture of metallic and non-metallic particles.
These cold spray powders allow for:
- the application of material coatings,
- repairing a surface with either similar or improved materials, or
- building up the component features by spraying onto a surface and then machining into the cold spray material.
Cold spray can create wear-resistant coatings, which improves the lifecycle of a component subject to severe conditions, such as atmospheric changes or saltwater. Cold spray can also provide a corrosion protection coating, perfect for marine and aerospace applications. In these heightened circumstances, it’s common to use bronze, stainless steel, zinc, aluminum, or even tantalum, to name a few of the available powders.
The cold spray process improves or repairs aluminum, nickel, or titanium aerospace components, among others. Modifying or restoring the original piece is often a more economical solution to completely replacing the component.
Why Is Cold Spray Used?
Cold spray is a “green” technology.
With no chemical heating and no melting in the process, there are no toxic fumes.
Also, the waste materials from the cold spray process are recyclable.
Plus, repairing (vs. replacing parts entirely) saves energy and reduces carbon dioxide emissions.
Due to the highly-focused particle spray path, it requires minimal masking of the substrate area.
Cold spray is easier on the substrate. There is no heat-affected zone.
There is also almost no oxidation, little alloy decomposition, or close to zero combustion product entrapment with the cold spray process.
Using cold spray technology is also an extremely cost-effective alternative to replacing the whole part.
As an illustration, a 40″ x 40″ panel on a B1 bomber can cost approximately $200k to replace with an 18-month lead time. Depending on the extent of the panel’s damage, you can repair this same panel using cold spray technology in days (as opposed to months) and for a fraction of the replacement’s price.
Portable cold spray equipment also makes cold spray the optimal solution for parts where removal is not an option.
What Is Thermal Spray?
Thermal spray is another coating deposition process. However, this process’s material is in the form of molten, or semi-molten, droplets sprayed onto a surface. The materials used are heated by either electrical or chemical means.
Typical thermal spray materials include metals, ceramics, and polymers but can consist of any material that melts or “becomes plastic” during heating. Typically, thermal spraying can apply coatings of .1 to 1mm in thickness. Sometimes thicker layers can be accomplished, but only in limited cases.
A thermal spray bond is mechanical, not metallurgical or fused. The substrate’s surface condition is critical. It must be thoroughly cleaned and roughened before thermal spraying.
There are several types of thermal spraying:
Arc spraying is a process that uses electricity to heat the coating material. An electrical arc initiates between the two coating materials, causing them to melt. Compressed air atomizes the metal coating and propels the droplets toward the substrate.
Flame spraying uses chemical heating. In this process, a fuel gas, such as propane or hydrogen and oxygen, mix to heat the coating material. The coating material is originally in either wire or powder form. Inert gas propels the coating to the substrate.
HVOF (High-velocity oxy-fuel) spraying is another chemically heat-produced process. The heat and pressure generated from combusting a liquid or gas fuel, combined with oxygen. The HVOF spray particles heat and expand in a chamber forcing the exhaust gases out at supersonic speeds towards the substrate.
Plasma spraying uses electrical means to heat the metal coating material. An electric arc forms a high-temperature plasma jet. The coating material feeds into the jet and inert gas, which expands rapidly to create a high-velocity spray of particles.
How Is Thermal Spray Used?
Like cold spray, thermal spray produces coatings on substrate materials, enhancing the original materials’ characteristics, modifying their appearance, or creating dimensional repairs.
The thermal spray helps manufacture and repair oil field equipment, diesel engines, gas turbines, and coating medical implants.
Why Is Thermal Spray Used?
One of the main thermal spray advantages is that thermal spray coatings can be applied at high deposition rates, but they generally lose strength and toughness at thicknesses greater than 1mm.
Thermal spray processes can be an alternative to:
- nickel plating,
- chrome plating,
- nitride treat processes,
- weld overlay,
- heat treat processes, or
Thermal spray can also sometimes repair parts at a fraction of the cost. Still, it depends significantly on the types of materials involved and the heat sensitivity of the component.
Thermal spray can also be utilized for wear-resistant coatings to extend a component’s life, but it comes with certain limits. The current limitations of these higher-temperature processes can be resolved with cold spray.
Cost-Effective Aerospace Maintenance & Repairs
Mid-America Aerotech is a certified FAA repair station located in West Fargo, North Dakota.
Our team proudly serves the military, aerospace, commercial industries, helicopters, and privately-owned airplanes. We offer cold spray repairs, production, and material testing. Contact us today for your aerospace maintenance and repairs.