In laser cladding, two types of lasers are commonly used: CO2 lasers and solid-state lasers.
The main types of lasers used in laser cladding are disc lasers, fiber lasers, and diode lasers. Older lamp-pumped lasers are becoming obsolete due to their low photoelectric conversion efficiency and maintenance difficulties.
There has been extensive research on continuous CO2 laser cladding, both domestically and internationally. The development of high-power solid-state lasers, particularly disc lasers, has been rapid and they are mainly used for surface modification of non-ferrous alloys.
According to literature, CO2 lasers are typically used for laser cladding of aluminum alloys, but the aluminum alloy matrix can easily become deformed or even collapse under CO2 laser irradiation. Solid-state lasers, especially disc lasers, have a shorter output wavelength of 1.06 μm compared to the CO2 laser wavelength, making them a more suitable choice for laser cladding of metals.
Laser cladding can be divided into two categories based on the method of powder feeding:
- Powder preset method
- Synchronous powder feeding
The two methods operate similarly.
The synchronous powder feeding method has the advantage of easy automatic control, high laser energy absorption rate, and a lack of internal pores.
Additionally, cladding cermet can greatly improve the crack resistance of the cladding layer and result in an even distribution of the hard ceramic phase throughout the cladding layer.
Laser cladding has the following characteristics:
(1) Fast cooling rate (up to 106K/s), which is a rapid solidification process. This makes it possible to obtain a fine crystal structure or a new phase that cannot be obtained through an equilibrium state, such as an unstable phase or an amorphous state.
(2) Low coating dilution rate (generally less than 5%). The coating is formed through a solid metallurgical bond or interface diffusion with the substrate. By adjusting laser process parameters, a coating with low dilution rate can be achieved, and the composition and dilution of the coating can be controlled.
(3) Minimal heat input and distortion. High power density rapid cladding can reduce deformation to the assembly tolerance of the part.
(4) Nearly unlimited powder options. High melting point alloys can be deposited on the surface of low melting point metals.
(5) Large cladding layer thickness. One-time powder feeding can produce a cladding layer with a thickness of 0.2 to 2.0mm.
(6) Selective welding is possible. This results in low material consumption and an excellent performance-price ratio.
(7) Beam aiming allows for welding in hard-to-reach areas.
(8) The process is easily automated and is well-suited for wear repair of common consumable parts in oil fields.
Similarities and differences between laser cladding and laser alloying
Both laser cladding and laser alloying use a rapid fusion process created by a high-density laser beam.
The result is an alloy coating with distinct compositions and properties that are formed on the substrate and bonded to each other.
Although the processes are similar, there are some key differences.
(1) The material used in laser cladding is fully melted, with a thin matrix melting layer. This minimizes the effect on the composition of the cladding layer.
In contrast, laser alloying adds alloying elements to the substrate surface to form a new alloy layer.
(2) In laser cladding, the metal powder on the substrate surface is not significantly melted, but the separate alloy powder is melted to form the cladding layer.
This creates a metallurgical bond with the thin melting layer of the base alloy.
The development of new materials through laser cladding technology is crucial for repairing and remanufacturing failed parts under extreme conditions, as well as for direct metal part manufacturing.
This technology is highly regarded by the scientific community and enterprises globally.