Additive manufacturing of metallic glasses (amorphous metals)
Highly elastic, extremely hard and corrosion-resistant: Bulk Metallic Glasses (BMGs).
1. Introduction: When metals solidify like glass
Normal metals have a crystalline lattice structure that forms when the melt cools. However, if special alloys (e.g. based on zirconium or titanium) are cooled extremely quickly (up to 1,000,000 °C per second), the chaotic, liquid arrangement of atoms "freezes" before crystals can form. The result is a "metallic glass" (Amorphous Metal or Bulk Metallic Glass - BMG).
Because 3D printing offers exactly these extreme cooling rates in the micro range, it is considered the key technology for processing these miracle materials.
The properties of amorphous metals
Due to the lack of grain boundaries and lattice defects (dislocations), amorphous metals are extremely hard (often twice as strong as high-strength titanium), highly elastic (they spring back with almost no loss of energy) and extremely corrosion-resistant. Mechanically they behave like plastic, but are as strong as the best steel.
2. The Challenge of the Critical Cooling Rate
Conventionally, amorphous metals can only be cast as extremely thin strips or very small components (a few millimeters thick). If the material in the core cools too slowly, it crystallizes and loses its unique properties (it becomes extremely brittle).
In powder bed 3D printing (PBF), however, only a tiny amount of powder (a 30 µm thin layer) is melted by the laser and immediately "quenched" (quenching) by the solid cold building plate or the underlying layers. This means that macroscopic, large components can be produced from amorphous metals for the first time.
3. Laser Powder Bed Fusion (PBF-LB) from BMGs
Printing metallic glasses is a science in itself:
- Heat affected zone: Each new melted layer reheats the amorphous layers already underneath. If the "glass transition temperature" is exceeded for too long, the material subsequently crystallizes (re-crystallization). The laser parameters must be kept extremely tight.
- Porosity vs. Crystallization: Too little laser energy leads to pores (poor fusion). Too much energy leads to heat build-up and crystallization. The process window is minimal.
4. Revolutionary fields of application
Where extreme wear resistance, elasticity and biocompatibility come together, amorphous metals from the 3D printer shine.
- Medical technology: Scalpels that never become dull, or highly elastic implants and stents that adapt perfectly to body movements and do not tire.
- Robotics and gears: Gears made of amorphous metals (e.g. in space travel or in exoskeletons) no longer require lubricant because they have an extremely low coefficient of friction and do not wear out (solid-state lubrication).
- Lifestyle and sensor technology: Housings for smartphones, sensors or luxury watches that are extremely scratch-resistant and do not dent in the event of a fall, but rather absorb the energy elastically.
5. Conclusion: A new age of materials science
The combination of additive manufacturing and amorphous metals eliminates the limitations of both technologies. While powder production (mostly expensive zirconium-copper-aluminum alloys) still has to become cheaper, the door to a completely new class of high-performance mechanical components through 3D printing is already wide open.