Additive manufacturing of copper-tungsten pseudoalloys
Liquid phase sintering for spark erosion electrodes and semiconductor heat sinks.
1. Introduction: The Fire and the Ice
Some industries require properties that no single element in the periodic table can provide. In high-voltage electrics, spark erosion electrodes (EDM) or heat shields in plasma technology, you need a material that conducts electricity and heat perfectly (like copper), but at the same time does not melt away at 3,000 °C and is extremely abrasion-resistant (like tungsten).
But copper and tungsten cannot be alloyed. Tungsten melts at 3,422 °C, copper at 1,085 °C (and evaporates at 2,562 °C). If you try to mix them as liquids, the copper will have long since dissolved into gas before the tungsten even becomes viscous. The solution is pseudo-alloys (Metal Matrix Composites - MMC) such as copper-tungsten (CuW), which are now being brought into completely new geometries through 3D printing.
What is a pseudo-alloy?
CuW is not a true chemical alloy (the atoms do not mix). It is a composite material. Under the microscope it looks like a sponge made of hard tungsten whose pores are completely filled with soft copper. Both metals retain their individual properties perfectly.
2. Conventional manufacturing vs. 3D printing
Traditionally, tungsten powder is pressed into a porous block, sintered in an oven and then soaked (infiltration) in a bath of liquid copper. The result is a primitive block that is extremely difficult to mill into complex heat sinks due to the tungsten.
Additive manufacturing (especially PBF-LB and Laser Metal Deposition LMD) now makes it possible to print this pseudoalloy directly into the final, highly complex final contour - including internal cooling channels for semiconductors (heat sinks).
3. PBF-LB: Melting without evaporation
Direct laser printing (PBF) of a CuW powder mixture is pure black magic.
- The laser must melt the tungsten powder (above 3,400 °C). In the millisecond in which this happens, the copper powder literally evaporates and creates enormous plumes and defects.
- The solution: You don't melt the tungsten at all! Modern processes use lasers that are precisely parameterized so that they only melt the copper (liquid phase sintering). The liquid copper flows like glue around the unmelted, solid tungsten particles, surrounds them and solidifies. The tungsten is not melted, but bound by the liquid copper.
4. Gradient materials: LMD-p
Even more fascinating is the use of laser powder deposition welding (LMD-p) for rocket nozzles.
A rocket nozzle needs 100% tungsten inside (where the hellfire of combustion burns). On the outside (where the cooling pipes run) it needs 100% copper. With an LMD system that has two powder conveyors, the component is printed continuously: You start with pure tungsten, add more copper powder layer by layer and end with pure copper. The result is a seamless rocket nozzle without weld seams - a so-called Functionally Graded Material (FGM).
5. Conclusion: Semiconductors and Hyper-Velocity
Copper-tungsten is an expensive niche material. But wherever arcs occur in high-voltage switches, where semiconductor chips (IGBTs) have to dissipate massive heat or where military railguns are fired, there is no alternative to CuW. The possibility of providing this actually "unmachinable" composite material with internal flow channels via 3D printing goes beyond the previous limits of thermal management.