3D printed Damascus steel

2020/09/10 — Damascus steel is hard yet tough because it consists of layers of different iron alloys. In ancient times, this was the material of choice, especially for sword blades. A team from the Max-Planck-Institut für Eisenforschung in Düsseldorf and the Fraunhofer Institute for Laser Technology in Aachen has developed a process that allows this type of steel to be produced layer by layer in a 3D printer. The hardness of each individual layer can be specifically adjusted. Such composites could be of interest for aerospace components or tools produced with 3D printers as the Max-Planck-Institut reports.

Celtic smiths combined various iron alloys (perhaps initially only to recycle the valuable iron) and thus obtained the material that later became known as Damascus steel or damask. It owes its name to the trading centre through which the composite material of oriental origin entered Europe.

Although there are currently ferrous alloys that are both hard and tough, they are often not specifically made for the 3D printing process. The scientists have developed a steel that consists of only a single starting material but is made up of alternating hard and ductile layers – a kind of Damascus steel, through 3D printing.

micro-structures harden the material

They developed an alloy consisting of iron, nickel, and titanium. At first, this alloy is relatively soft. »Under certain conditions, small nickel–titanium micro-structures form. These, so-called precipitates, harden the material«, explains Philipp Kürnsteiner, post-doctoral researcher at the MPIE.

In order to be able to create the nickel–titanium structures, the researchers interrupt the printing process for a certain time after each newly deposited layer. The metal cools down to below 195°C. »Below this temperature, a transformation of the crystal structure occurs in the steel«, explains Eric Jägle, head of the »Alloys for Additive Manufacturing« group at the Max-Planck-Institut für Eisenforschung and, since January 2020, professor at the University of the Bundeswehr Munich.

In their experiments, the researchers produced cube-shaped or cuboid steel pieces with side lengths of a few centimeters as models for objects with more complex geometries. They also emphasize that the Damascus-like steel with its periodically changing layers is only one example of locally influencing the micro-structure of an alloy during the manufacturing process. For example, it is equally possible to create tool components with a continuous soft core surrounded by a hard, abrasion-resistant outer layer.