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Laser surface alloying is an advanced material processing technology that utilizes the high power of density from a focused laser source to produce an extremely dense and crack-free structure by heating and melting a surface while injecting alloy elements or compound powder on to the surface.
The technique uses a laser beam as a source of energy; a coating material is deposited onto the base material, and the coating and base material is targeted by a laser which fuses or alloys the materials together. The laser bonding results in new components with highly resistant surfaces against wear at both high and low temperatures.
Overview of Material Processing Technology
The material surface properties can be influenced by the addition of alloying powders, which form intermetallic compounds via a chemical reaction between the powder and the material. These compounds are a solid phase consisting of two or more metallic elements in precise proportions, generally characterized as hard materials.
The melting occurs very quickly and only at the surface so the majority of the material remains cool and acts as a heat sink. There is a large temperature gradient across the boundary between the melted surface region and the underlying solid substrate, which results in rapid self-quenching and re-solidification.
The process is attractive because a wide variety of chemical and microstructural states that can be retained because of the rapid quench from the liquid phase. This will include chemical profiles where the alloyed element is highly concentrated near the atomic surface and decreases in concentration over shallow depths. It also includes uniform profiles where the concentration is the same throughout the entire melted region.
To achieve the desired enhanced surface properties, it is necessary to control the laser power, beam diameter, laser scanning speed, and powder feed rate. The process parameters play an important role in both surface quality and microstructure.
Laser Surface Alloying
Laser surface alloying offers clear and significant advantages over standard welding, cladding or hard facing. It is a better technique for coating various shapes and can increase the lifetime of parts by six to seven years. It can also minimize the amount of base material diluted during the process, which allows the coating materials to retain many of its original properties.
By implementing the proper laser beam parameters, the heat input can be drastically reduced compared to other alloying, surfacing or cladding methods. This can lower the size of the heat-affected zone, and this enables the base material to hold much of its unique assets. This also means shorter cooler times leading to coatings with high hardness and excellent wear resistance.
The coating can be applied in a variety of ways, but as a film of around 100 microns is most common; this thickness doesn’t require too much energy to melt. It could also be applied as a powder that is continuously fed to the base material in front of the laser beam.
Aluminum and its Alloys
Aluminum is the second most used metal after steel; it has excellent electric conductivity, high strength to weight ratio and high corrosion resistance. Aluminum and its alloys are widely used in aerospace, automotive and transportation industries. Modifying its surface is of crucial importance to the surface properties of the metal and its alloys since the high coefficient of friction, wear characteristics and low hardness have limited long term performance.
The metal is commonly alloyed with copper, zinc, magnesium, silicon, manganese, and lithium, and sometimes small amounts of chromium, lead, bismuth, nickel, titanium and zirconium.
Applications of Laser Surface Alloying
Applications of laser surface alloying include items that need increased wear resistance such as certain areas of tooling. It can also help increase the corrosion resistance of base materials. Using corrosion-resistant materials on the surface of susceptible base materials can greatly enhance resistance to oxidation, so long as the materials are compatible with one another.
Sources and Further Reading
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