Laser Cladding vs. Thermal Spray
How to Know Which Hardfacing Method is Best for You?
We live in the information age; you can find the answer to almost any question in minutes. Doing a simple internet search for “machine part repair” or “remanufacture” will result in thousands of ways and processes to rebuild your parts and get them working again. The hard part is figuring out which advice to take and who to trust. The even harder part comes when there are multiple kinds of repair processes that seem, at first glance, to do the same job. If you have ever wondered what the difference is between laser cladding and thermal spray and which one is right for you, then you’ve landed in the right spot.
Same But Different
In the broad scheme of things, laser cladding and thermal spray accomplish the same goal. They can be used to add a hardened, new surface to previously damaged or worn industrial components. They can perform remanufacture and even prevent future wear.
Most people look to laser cladding due to its metallurgical bond but there are thermal spray processes that can achieve this as well. So, which one should you choose? Let’s break it down and look at each one individually.
Laser cladding is a hardfacing process that uses laser energy to melt and weld powder material to a surface. The result is similar to hardface welding but operates at a much lower temperature; around 1000°F as opposed to 11,000°F for TIG welding. It forms a metallurgical bond with the substrate material and produces a hard, wear resistant coating.
Laser Cladding Advantages
The biggest advantage to laser cladding is the metallurgical bond achieved at relatively low temperatures. Since laser cladding uses metallurgical bonding, there is little to no porosity in the coatings, resulting in fantastic long-term corrosion resistance.
One-Step Build Up Process
Laser cladding also allows for thicker build up on a single pass compared to other processes. Overlapping passes meld together to produce a quality surface. This combined with low metal dilution, means there is minimal post-process machining.
Laser Cladding Disadvantages
Laser cladding is a mostly robotically controlled process. While this creates greater precision, it also less versatile. Not only is the system not portable, it can create complication for larger parts.
Laser cladding typically only applies a few materials. Nickel and cobalt-based alloys such as Inconel®, Hastelloy® and Stellite®. Some stainless steels, such as 300 and 400 series, and carbides, such as tungsten carbide. These are great for wear and corrosion resistance but can fall short if you require other coating properties.
Coating Thickness Issues
Like most advantages, thick build up, also has its downside. Since laser cladding lays down so much in one pass, it can struggle when thin coatings are required. High build rate can also lead to cracking.
Thermal Spray encompasses a wide variety of processes. Most use a gas or electricity to create a flame in order to melt the wire or powder materials and apply them to a substrate. Some, such as spray and fuse, produce metallurgical bonding; while most others use mechanical bonding.
Thermal Spray Advantages
Wide Variety of Materials
Thermal spray can be used to apply a variety of materials, including the materials used in laser cladding. Additional material options can be used to supplement the coating properties. In addition to wear and corrosion resistance, thermal spray coatings can be used to create dielectric, thermal barrier and electrically conductive coatings. One thermal spray process, Arc Spray, can feed two different materials to produce an engineered alloy coating.
Thin Coating Capabilities
Thermal spray processes can lay down coatings as thin as 0.002”, thinner in some cases. The ability to spray in thin layers can also aid in producing coatings in situations when precise coating thicknesses are required. Thermal spray can also build up thicker coatings by doing multiple, robotically controlled passes.
Due to its versatility, thermal spray can also be sprayed in the field. Unlike laser cladding, thermal spray guns can be operated independently of robotics and can produce quality coatings with skilled operators. The typical robotically controlled thermal spray set up can also handle intricate geometries without thick build up in corners and on edges.
Thermal Spray Disadvantages
Requires Multi-Step Process and Skilled Technicians
Thermal spray can require more masking to protect against overspray compared to the focused spray area of laser cladding. Since most thermal spray processes use mechanical bonding, machining and grit blasting are usually required before coating application which can lengthen the process.
Higher Operating Temperature
Spray and fuse thermal spray can accomplish metallurgical bond but at a higher heat than laser cladding, around 1,900°F to 2,050°F. High Velocity Air Fuel, or HVAF Spray, is lowest in temperature at around 3,500°F and is mechanically bonded.
Presence of Porosity and Oxides
Depending on the process you use, there is low to high porosity for thermal spray coatings. This can be a long-term issue with certain coating materials in highly corrosive environments if not sprayed correctly. Porosity helps minimize coating stress and reduces cracking but also interferes with surface finish, strength and microhardness. Oxides are introduced during the thermal spray process, which can increase hardness and wear resistance, but can also cause corrosion, strength and machinability issues.
Different Needs, Different Processes
Both thermal spray and laser cladding can produce wear and corrosion resistant coatings. There are advantages and disadvantages to both. The best way to choose is to decide what exactly it is you’re looking for in a surface repair or coating. If you need a metallurgical bond and temperature is an issue, then laser cladding is the way to go. If you need a thin coating of material, then you should look to thermal spray. If you need your coating to do something other than just wear and corrosion resistance, you should look at the different coating materials possible with thermal spray. Depending on your situation, either one may work, and you might be better off getting a quote for each process and seeing how they compare in cost for your specific part.