Lasers used in laser cladding mainly include CO2 lasers and solid-state lasers.
It mainly includes disc lasers, fiber lasers and diode lasers.
Old-fashioned lamp-pumped lasers have gradually faded out of the market due to low photoelectric conversion efficiency and cumbersome maintenance.
For continuous CO2 laser cladding, domestic and foreign scholars have done a lot of research.
The development of high-power solid-state lasers is rapid, mainly used for surface modification of non-ferrous alloys.
According to reports in the literature, the laser cladding of aluminum alloy is carried out by CO2 laser, and the aluminum alloy matrix is easily deformed or even collapsed under the condition of CO2 laser irradiation.
Solid-state lasers, especially disc lasers, have an output wavelength of 1.06 μm, which is one order of magnitude smaller than the CO2 laser wavelength, making them more suitable for laser cladding of such metals.
Laser cladding can be divided into two categories according to the different powder feeding process:
- Powder preset method
- Synchronous powder feeding
The two methods work similarly.
The synchronous powder feeding method has easy automatic control, high laser energy absorption rate and no internal pores.
In particular, cladding the cermet can significantly improve the crack resistance of the cladding layer and make the hard ceramic phase evenly distributed in the cladding layer.
Laser cladding has the following characteristics
(1) The cooling rate is fast (up to 106K/s), which belongs to the rapid solidification process.
It is easy to obtain a fine crystal structure or a new phase which cannot be obtained by an equilibrium state, such as an unstable phase or an amorphous state.
(2) The coating dilution rate is low (generally less than 5%).
It is a solid metallurgical bond or interface diffusion with the substrate.
By adjusting the laser process parameters, a good coating with low dilution rate can be obtained, and the coating composition and dilution can be controlled.
(3) The heat input and distortion are small.
Especially when using high power density rapid cladding, the deformation can be reduced to the assembly tolerance of the part.
(4) There is almost no limit to the choice of powder.
In particular, a high melting point alloy is deposited on the surface of a low melting point metal.
(5) The thickness of the cladding layer is large.
The thickness of one-time powder feeding is 0.2~2.0mm.
(6) It is possible to carry out the selection welding.
Low material consumption and excellent performance-price ratio.
(7) Beam aiming can weld hard-to-reach areas.
(8) The process is easy to automate.
It is very suitable for the 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 fast-reading fusion process produced by a high-energy density laser beam.
An alloy coating having completely different compositions and properties formed on the surface of the substrate and fused to each other.
The process is similar, but there are essential differences.
The main differences are as follows:
(1) The coating material in the laser cladding process is completely melted, and the matrix melting layer is extremely thin, so that the composition of the cladding layer is minimally affected.
Laser alloying involves the addition of alloying elements to the surface of the substrate, in order to form a new alloy layer based on the substrate.
(2) The laser cladding does not substantially melt the metal powder of the surface layer of the substrate as a solvent, but melts the alloy powder separately disposed to form a subject alloy of the cladding layer.
At the same time, the base alloy also has a thin layer of melting, forming a metallurgical bond with it.
The preparation of new materials by laser cladding technology is an important basis for the repair and remanufacture of failed parts under extreme conditions and the direct manufacture of metal parts.
It is highly valued by the scientific community and enterprises all over the world.