What are the principles and advantages of supersonic spraying? How to choose materials for supersonic spraying?

What are the principles and advantages of supersonic spraying? How to choose materials for supersonic spraying?

Here is a detailed introduction to the principle, advantages, and material selection methods of supersonic spraying:

Principle of supersonic spraying

Supersonic spraying is a thermal spraying technology based on gas dynamics and the process of material heating and melting. Specifically:

Accelerating gas generation: By using a specially designed spray gun, high-pressure gases (such as compressed air, nitrogen, argon, etc.) are introduced into the interior of the spray gun. These gases are accelerated by the Laval nozzle structure of the spray gun, forming a supersonic airflow that can reach several times the speed of sound.

Powder conveying and heating: At the same time, the sprayed material is conveyed in powder form to the spray gun through a powder feeder. The powder is mixed with high-speed airflow inside the spray gun and sent into the high-temperature area. Generally, high temperatures are generated through combustion or plasma to rapidly heat powder particles to a molten or semi molten state.

High speed spray deposition: Powder particles in a molten or semi molten state are propelled by supersonic airflow and sprayed at extremely high speeds onto the surface of the workpiece to be sprayed. After these high-speed particles collide with the surface of the workpiece, they quickly spread, solidify, and accumulate layer by layer, forming a uniform and dense coating.

Advantages of supersonic spraying

High coating quality

High bonding strength: Due to the high-speed impact of powder particles on the surface of the workpiece, they have high kinetic energy and can form a good mechanical bite and physical chemical bond with the workpiece surface, greatly improving the bonding strength between the coating and the substrate, generally reaching over 50MPa.

Good coating density: particles flying at high speeds can stack more tightly together, and the porosity of the coating can usually be as low as 1% or less, effectively improving the coating's corrosion resistance, wear resistance, and other properties.

Wide adaptability of materials

Metal materials: can be sprayed with various metals and alloys, such as stainless steel, nickel based alloys, copper alloys, etc., to improve the corrosion resistance, wear resistance, and conductivity of workpieces.

Ceramic materials: Ceramic materials such as alumina and zirconia can also form high-performance coatings through supersonic spraying, which are used for high temperature resistance, insulation, and other applications.

Composite materials: Different materials such as metals and ceramics can be mixed and sprayed to prepare composite material coatings with comprehensive properties.

High spraying efficiency

Fast speed: The spraying speed of supersonic spraying is much higher than traditional spraying methods, which can complete large-area coating preparation in a shorter time and improve production efficiency. For example, in the spraying operation of some large workpieces, the spraying time can be significantly shortened.

Uniform thickness: Due to the high-speed and uniform spraying of sprayed particles, a coating with uniform thickness can be formed on the surface of the workpiece, reducing subsequent processing steps and lowering production costs.

Small impact on the substrate

Low thermal impact: Compared with some traditional surface treatment methods, the substrate heating temperature during supersonic spraying is relatively low, generally below 200 ℃, thereby reducing the impact on the properties of the substrate material and avoiding deformation and structural changes of the substrate.

Low stress: The internal stress generated during the formation process of the coating is relatively small, which is not easy to cause cracking or peeling of the coating, and improves the stability and service life of the coating.

Method for selecting materials for supersonic spraying

Choose according to the usage environment

High temperature environment: If the workpiece is used in a high temperature environment, such as the combustion chamber components of an aircraft engine, ceramic materials or high-temperature resistant alloy powders can be selected, such as yttria stabilized zirconia, nickel chromium aluminum yttrium alloy, etc. These materials have good high-temperature resistance and thermal stability.

Corrosive environment: Workpieces working in corrosive media, such as chemical equipment, marine facilities, etc., should use metal or alloy powders with corrosion resistance, such as stainless steel, nickel based corrosion-resistant alloys, or ceramic materials such as silicon carbide, to resist chemical corrosion.

Wear environment: For workpieces that are subject to wear, such as mechanical parts, molds, etc., materials can be selected according to the type of wear. For abrasive wear, hard alloy powders such as tungsten carbide and chromium carbide can be used; For adhesive wear, composite powders of materials such as molybdenum disulfide and boron nitride with self-lubricating properties mixed with metals can be selected.

Select based on coating performance requirements

Hardness requirement: If a coating with high hardness is required to improve wear resistance and scratch resistance, ceramic materials or high hardness metal ceramic powders such as alumina, titanium nitride, etc. can be selected.

Conductivity requirements: For applications that require coatings with good conductivity, such as electrode coatings for electronic components, metal powders such as copper, silver, gold, etc. should be selected.

Insulation requirements: In cases where insulation is required, such as insulation coatings for electrical equipment, ceramic materials such as silicon oxide and aluminum nitride can be selected.

Select based on the characteristics of the spraying process

Particle size matching: Different spray guns and spraying processes have certain requirements for powder particle size. Generally speaking, supersonic spraying should use powders with a particle size of 15-53 μ m to ensure the transportation and heating effect of the powder in the spray gun, as well as the deposition quality on the surface of the workpiece.

Liquidity: The fluidity of powder directly affects the stability and uniformity of powder feeding. Good flowability powders should be selected, usually by adding appropriate lubricants or surface treatment to improve their flowability.