Surface alloying by Laser Metal Deposition (LMD)
Laser hardening and mixing customized gradient materials (graded materials).
1. Introduction: Custom-made metal skin
The design of machines is often subject to a dilemma: the core component (e.g. a huge roller in the paper industry or a drill bit in oil mining) must be tough, break-resistant and, above all, cheap. However, the surface must be extremely hard, corrosion-resistant or abrasion-resistant.
The solution is called Laser Metal Deposition (LMD) for surface alloying. In contrast to pure coating (cladding), in which a hard metal layer is applied, laser alloying aims to permanently change the chemical composition of the surface by melting completely new elements.
Surface alloying vs. coating (cladding)
Cladding creates a new, separate layer (track) on the component. During laser alloying, the LMD head blows powder (e.g. carbon, chromium or boron) into a melt pool on the component surface, where the base material is melted deeply (1 to 3 mm). The supplied elements mix (dilution) with the liquid base steel. After solidification, the outer layer has chemically transformed into a completely new, ultra-hard alloy.
2. The magic of the powder mixture
LMD-p (powder-based LMD) often has several powder conveyors that work independently of each other.
An engineer can change the mixture during the welding process (Graded Materials). It starts with 100% mild steel (perfect bond to the core), then gradually adds chromium and molybdenum, and finishes the top millimeters with an extremely hard, cobalt-based hard alloy. This creates smooth, crack-free transitions (gradient materials) from soft to ultra-hard, which is not possible with any other manufacturing method in the world.
3. Laser hardening and surface layer finishing
Even without the addition of powder, the LMD laser head is a powerful tool for surface refinement.
- Laser remelting: The defocused laser moves over cast iron and melts the top layer. Due to the rapid cooling (self-quenching), the material solidifies extremely fine-grained and hard (e.g. ledeburitic). Microcracks and pores in the casting are eliminated.
- Local hardening: The laser moves exactly along the heavily stressed edges of a punching tool, heats the steel precisely (below the melting point) and thus selectively hardens only the cutting edge, while the rest of the tool remains ductile.
4. Applications in industry
Surface alloying using LMD is indispensable in wear-intensive industries:
- Mining & Oil Drilling: Drill heads (drill bits) are armored with tungsten carbide (WC) particles (matrix bits). The tungsten carbide grains are embedded by the laser in a tough steel or nickel matrix.
- Forming tools: Large pressing tools in the automotive industry have a locally alloyed, wear-resistant armor layer on the bending edges.
5. Conclusion: Alchemy with light
Laser Metal Deposition is more than just 3D printing. It is a metallurgical alchemy kit. The ability to change the chemistry of a component precisely and locally using laser energy extends the service life of heavy industrial systems enormously, saves gigantic amounts of expensive special alloys (which would otherwise have to be used for the solid material) and massively reduces the environmental impact.
