Skoltech prints alloy ideal for jet engines

Researchers from Skolkovo Institute of Science and Technology, or Skoltech, in Moscow, Russia, have leveraged 3D printing to forge an unlikely union between one of Man's oldest known alloys, bronze, and one of its relatively newer discoveries, steel, that could be used to manufacture combustion chambers for aircraft and rocket engines.

This 3D-printed Skoltech alloy, simply named bronze-steel, simultaneously benefits from steel's ability to withstand extreme temperatures and bronze's capacity to conduct heat away from the chamber to prevent engines from overheating.

"3D printing is promising for manufacturing composite parts, endowed with the properties of the two distinct materials that make up the composite," said Igor Shishkovsky, associate professor of Skoltech Materials. "Consider, for example, that steel is resistant to the high temperatures created by fuel combustion in an operating engine. This is great, but compared with bronze, steel is a modest thermal conductor, so the engine coolant cannot siphon heat away from it as effectively to prevent overheating and damage."

As the principal investigator on the study, Shishkovsky reported that the first-ever synthesis of a bronze-steel alloy was done using direct laser deposition, one of the most widely used techniques in the 3D printing space.

The Skoltech team combined bronze and steel in two different ways, achieving so-called quasi-homogeneous alloys and sandwich structures. The former; two materials are more or less evenly intermixed throughout the sample, while sandwich structures consist of a series of alternating 0.25-millimeter-thick layers of bronze and steel.

"With 3D printing, you can actually get the best of both worlds by manufacturing a combustion chamber that seamlessly goes from being bronze on the inside for better temperature management to being steel on the outside for holding the structure together," said Shiskovsky.

The researchers used one type of steel but varied its content in the alloy from 25% to 50% and experimented with three different common varieties of bronze.

Ultimately, the study confirmed that the two materials fused well, without defects.

To do this, the team grew vertical bars from the bottom up and examined their shape, chemical composition, and microstructure.

"When something goes wrong, the sample's shape might get visibly distorted or it might fracture into layers during 3D printing," explained Shiskovsky. "This usually means that either the materials used are not suitable or the conditions haven't been set right."

Upon finding the ideal materials and settings, the researchers proceeded to cut out tiny pieces from different parts of the samples and investigated their internal structure with optical and scanning electron microscopy. The main mechanical characteristics were then obtained through a wide range of stress tests, which the researchers reported for the first time.

"Now that we have confirmed that steel and bronze can be combined in an alloy and are compatible with 3D printing via direct laser deposition, and we know the mechanical characteristics of the new material, we can explore its possible applications," said Konstantin Makarenko, first author on the study and a fourth-year Ph.D. student at Skoltech. "Looking forward, I would like to manufacture and test a steel-bronze combustion chamber at Skoltech, but beyond that, other items are possible and other metal combinations could be used."

The team believes the next step would be to create turbine blades made of a strengthened superalloy with cooling channels made of bronze.

"It's all about combining the benefits of two distinct materials in one seamless product without any welding or other junctures," finished Makarenko.