Amorphous metals’ disordered atomic structure leads to better 3D-printed parts

Amorphous alloys and additive manufacturing yield strong, hard, flexible parts

Sennheiser opted to 3D-print the housing of its new IE 600 headphones from Heraeus AMLOY Technologies’ AMLOY-ZR01 amorphous metal. The zirconium alloy offers triple the hardness and flexural strength of high-performance steel. Sennheiser

Two German industry heavyweights have teamed up to help ensure the success of a novel material for 3D-printing applications. Heraeus AMLOY Technologies GmbH and the additive manufacturing division of the TRUMPF Group are working to optimize the process of printing parts from Heraeus’ zirconium-based alloys on TRUMPF TruPrint printers.

The Heraeus materials, AMLOY-ZR1 and AMLOY-ZR2, fall into the category of amorphous alloys, also known as amorphous metals or metallic glasses.

Amorphous alloys are formed by shock-freezing a metallic melt, Heraeus explains. Because of supercooling, the atoms solidify in a disordered—amorphous—manner and have no opportunity to form a crystalline lattice. Defects in the lattice structure of conventional metals influence their mechanical and electromagnetic properties, causing them to corrode, become brittle, or crack. Amorphous metals don’t exhibit these flaws.

Defects in the lattice structure of conventional metals influence their mechanical and electromagnetic properties, causing them to corrode, become brittle, or crack. Amorphous metals don’t exhibit these flaws.

A key mechanical characteristic of amorphous alloys is that they are isotropic, meaning components made from them exhibit the same mechanical properties in all directions. Isotropic behavior simplifies product design and specifications and facilitates the creation of large components and complex geometries.

Another distinguishing feature of amorphous alloys is that they offer material properties that normally exclude each another—specifically, high hardness and strength along with elasticity.

AMLOY-Zr02 has a hardness of 540 HV (Vickers hardness), which is more than twice that of 316L stainless steel, and Zr01 has a hardness of 480 HV. Products made from these materials are highly scratch-resistant.

That appeals to Swedish watch manufacturer Oskar Pascal. It produced the world’s first watch-case made from AMLOY-Zr01.

“If you have scratches on your watch case, that’s not cool,” noted TRUMPF material expert Christian Schauer.

Amorphous metals are formed by shock-freezing a metallic melt. This prevents lattice crystallization of atoms. The resulting disordered, or amorphous, structure resists corrosion, brittleness, and crack formation. Heraeus AMLOY

Amorphous alloys also provide yield strength exceeding 1,300 MPa, which is more than three times that of 316L. High strength makes it easier to produce smaller, thinner, and lighter components in industries such as automotive and aerospace.

To help ensure successful 3D printing of the metals, Zr01 and Zr02 are designed to cool at the proper rate for the SLM process, and TRUMPF optimized its printers for the materials.

Additionally, amorphous alloys have elasticity modulus values less than half that of 316L (87 GPa for AMLOY-Zr01 and 89 GPa for AMLOY-Zr02). Their elastic elongation of almost 2% is beneficial in the production of sensors, flexure joints, and implants. The latter is just one of many possible medical applications for the biocompatible materials.

Other useful properties of amorphous alloys include good ductility, which allows them to be hammered thin or stretched into wire without breaking, and corrosion resistance, which extends product life.

To help ensure successful 3D printing of the metals, Zr01 and Zr02 are designed to cool at the proper rate for the SLM (selective laser melting) process, and TRUMPF optimized its TruPrint 1000 and 2000 3D printers for the materials.

For one thing, “amorphous structures need a very high cooling rate from the melt to the solid state,” Schauer explained. Featuring a beam diameter of just 55 µm, the TruPrint 1000 and 2000 produce small melt volumes in which a cooling rate of 200 K/sec. can be maintained to prevent the amorphous metals from crystallizing.

In addition, the small beam diameter is key to the creation of high-quality surfaces that simplify, or even eliminate, the need for refinishing processes.

The TruPrint 2000’s two 300-W lasers scan the entire build volume in parallel so amorphous components can be manufactured in series. During the printing process, problems are detected early on, thanks to monitoring of the machine condition, powder bed, and melt pool, according to TRUMPF.

Recently, AMLOY-Zr01 was chosen for the 3D-printed housing of the new IE 600 earbuds from Sennheiser. The material’s high hardness provides good scratch-resistance, Schauer noted. In addition, its low thermal conductivity is an asset, particularly in cold weather.

“If the earbuds were made of aluminum (which has very high thermal conductivity) and the temperature were -10 degrees C, then the material would also be -10 degrees,” Schauer said. “So I don’t think you could wear them in your ears.”