What materials can be printed on metal? The honest list

Laser powder bed fusion (LPBF) can, in practice, produce almost any weldable alloy. And that's the rule that best predicts the outcome: LPBF is spot welding repeated millions of times, so a material that cracks when welded will also crack when printed. From there, the list divides into three very distinct groups: those that are mature, those that are being qualified, and those that won't make it.

The ripe ones

These are the ones with a known processing window, can be bought in powder form without any problem, and have been in actual production for years.

Of these, the ones that cause the fewest problems at the beginning are 316L and AlSi10Mg: they have the widest processing window and are more forgiving of parameterization errors. Titanium and copper are the most demanding, each for a different reason.

Why copper was difficult for so long

This deserves a paragraph because it explains the physics of the process well. Pure copper reflects most of the infrared light from a conventional fiber laser and also conducts heat exceptionally well. The two of these things together mean that the small amount of heat that enters is immediately dissipated.

This has been resolved in two ways: green wavelength lasers, which copper absorbs much better, and alloys like GRCop-42 or CuCrZr, which retain much of their conductivity and are considerably more processable than pure copper. The second approach is the one that has led to copper's actual production.

Those that are on their way

• Refractories: tungsten, molybdenum, niobium. They can be printed, but tend to crack due to their low-temperature brittleness. This is an area of ongoing research.
• High-strength aluminium alloys from the 6000 and 7000 series. Traditional aluminium alloys crack when hot during welding. Variants specifically designed for additive manufacturing are being developed.
• High-carbon steels. The carbon content makes them hard, but they are also prone to cracking during the rapid cooling process.
• Magnesium. Extremely lightweight and biodegradable, making it very interesting for temporary implants. However, it is extremely reactive in powder form, which greatly complicates installation.
• Metallic amorphs and high-entropy alloys. Very promising in the laboratory, but far from production.

Those that don't

• Alloys with elements that evaporate. Zinc boils well below the melting bath temperature, so brass decomposes when laser melted: the zinc evaporates, and what remains is not brass.
• Free-cutting materials with lead or sulfur. The additives that facilitate machining are precisely what ruin the weld.
• Almost any alloy designed for casting without adaptation. They are formulated to solidify slowly in a mold, not in milliseconds.

Four questions before choosing

1. At what temperature does the part operate? Above approximately 500 °C sustained, the choice is reduced to nickel.
2. Is weight or cost the deciding factor? Titanium if weight is a factor; aluminium if not.
3. Does it come into contact with the human body? CoCr and titanium are biocompatible.
4. Does it need to dissipate heat? Aluminium for most, copper when pressure and temperature are also involved.

Almost always, with those four answers, only one candidate remains. When two remain, the price of the powder decides.

A notice about property tables

You'll see data sheets with yield strength, elongation, and density to two decimal places. Read them carefully: in LPBF, these values depend on the manufacturing orientation, the sweep strategy, the layer thickness, and the subsequent heat treatment. The same alloy, on the same machine, will yield different results depending on how the part was positioned.

A number without the conditions under which it was measured means nothing. If a supplier gives you one without the other half, ask for it.

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The seven alloys we're working with today, along with their specific uses, are listed in the materials catalog. How this powder is manufactured and why it's expensive can be found in how-metal-powder-is-manufactured. If you need to test an alloy without committing to an entire batch, that's what SamyFlex is for. Why the laser's color determines which metals can be melted is explained in what-is-a-laser. And the three alloys that handle most projects are compared in 316L, Inconel 718, or Ti-6Al-4V.