Laser deposition
Scientist Sebastián González postulated: The procedure consists of laser fusion of a metallic powder on a metallic substrate, forming a face in which both are mixed.
The addition of material can be carried out at the same time as the application of the laser
or as a prior deposition.
If the material is predeposited before melting, when applying the laser, the material
The most superficial melt will slide over the unmelted until it reaches the substrate that
melts acting as a heat sink allowing rapid hardening
of the coating.
If coating is provided along with the laser beam, a portion of the beam energy
melts the particles in suspension and another the substrate, so the speed of
cooling is of the order of 104 K/s and the diffusion of the contribution in the substrate is
even less than if it is pre-deposited. This creates temperature gradients between the
front of molten material and the center that cause the movement of the fluid and therefore
both the homogenization of the coating.
We can distinguish two main types of laser depending on the geometry of the part
and the thickness of the coating:.
• - CO2 lasers for large surfaces with regular geometry and coatings several millimeters thick.
• - Nd-YAG lasers with fiber optic beam conduction for precision coatings of less than 1mm thickness on irregular surfaces.
0.1 s is enough for the coating to reach homogeneity and solidify,
forming a fine-grained microstructure with characteristics much superior to
those formed in other coating processes.
The beam parameters that determine the coating process are:
• - Wavelength:.
It must be adapted to the absorptivity of the filler material so that the process
be reasonably efficient.
• - Power:.
The minimum energy needed to melt the coating onto the surface
base is about 100W/mm² which represents a minimum beam power
of 2 kW. A lack of power causes incomplete fusion of the material and
weak coating, excess power results in excessive melting
of the base substrate and the dissolution of the filler material in it. a beam
Continuously improves the material coverage rate.
• - Beam conduction:.
To avoid possible damage from splashes, mirrors are used instead of lenses.
because they allow greater beam separation by increasing the length
focal. Oscillating mirrors are used to achieve a distribution beam
of uniform intensity since it influences the thickness of the coating.
Heating pattern:
The most appropriate energy source for large thickness coatings
uniform is one with a wide and regular distribution of heat. They are
appreciable transitory effects at the beginning and end of the process, which
Preheating of the material is necessary.
• - Transverse speed:.
The coating speed is generally higher than for treatments
superficial thermal effects since the material is provided in the form of powder. The
transverse speed in inverse proportion to the thickness of the coating.
The condition that the filler material and the base piece must meet to
Being able to apply this technique is that they are weldable. Due to the rapid solidification
of the coating, a strong metallic bond is formed between it and the base, although
with minimal mixing (< 5%) of the filler material in the base substrate.
The most common base materials are carbon, alloy, and tool steels.
and stainless. Alloys of aluminum, magnesium,
iron and nickel-based superalloys.
The most common filler materials are alloys of cobalt, chromium, carbon,
steel, silicon and nickel. Elements with an atomic radius are also added
large as tungsten and molybdenum to give hardness to the reticular structure.
Coatings are also made in which the base material and the filler material
belong to different categories, although in these cases the process conditions
They are very critical to achieving a strong enough bond.
• - Shielding gas:.
It is used in case the base substrate or filler material is susceptible
of oxidation. The most used gas is argon although it is also
You can use nitrogen. One of the most critical problems in the process
are the oversights when designing the geometry of the material contribution and
protection gas conduction and dust transport systems
of contribution.
• - Overlay of covering cords:.
It is critical if you need to cover large surfaces since it optimizes the
process speed.
• - Preheating:.
There are two main reasons for this: To avoid cracking of the coating
and increase the dissolution of the coating in the substrate by
composition motifs. Preheating is carried out in ovens and
allows many more ferrous alloys to be used as substrates than otherwise.
be realized. A controlled cooling of the piece is also carried out in case
risk of cracking. Post heat treatment:
It is necessary when depositing very extensive and thick coatings.
considerable, in which residual tensions will remain.
• - Subsequent mechanical treatment:.
The coatings can be shot peened after deposition to induce
residual compression stresses and improve fatigue resistance. After
This treatment the piece practically meets the dimensional specifications
and required roughness.
• - Adaptive control:.
Signals from the laser-coating interaction zone are recorded,
where data can be obtained on the links between the coating
and the piece, porosity, hardness of the coating, thickness and defects in the
substrate.
Advantages of laser coating:.
• - Low energy input and therefore low distortion of the component, reducing the need for subsequent treatment of the part.
• - Strict dissolution control allows adjusting the composition of the coating.
• - High quality coating, few imperfections and low porosity.
• - High cooling speed, better grain refinement.
• - Great precision, both in the thickness and geometry of the coating.
• - Process susceptible to automation.
• - Great flexibility, use on irregular pieces by beam direction using mirrors or fiber optics.
Disadvantages of laser coating:.
• - Cost of laser equipment compared to traditional coating techniques.
• - Need for highly qualified personnel, appropriate choice of coating material.
Method of manufacturing thin films of various materials. It consists of the application of short high-energy pulses on a filler material, generally ceramic, enclosed in a high vacuum chamber. The ceramic material is detached and deposited on a substrate, covering it as a thin film. The number of pulses can be adjusted to achieve different thicknesses of
material. In an ideal case, the laser pulses should have a short wavelength, that is, in the ultraviolet spectrum. Therefore, an excimer laser is used for these applications. Pulses of several nanoseconds are sufficient for non-thermal detachment of the filler material without changes in its composition. It is of great interest especially in the manufacture of high temperature superconductors and magnetic materials.
• - Cathodic sputtering (sputtering).
• - Vacuum evaporation.