Research group has made a defect-resistant superalloy that can be 3-D-printed

Additive manufacturing of superalloy based on cobalt-Nickel (CoNi) by electron beam melting (EBM) and selective laser melting (SLM). Shown (from left to right): micrographs obtained by scanning electron microscopy (SEM), SB – CoNi-10 alloy metal powder used for a) EBM and b) SLM testing-printing simple geometric shapes (c, d) printed for uniaxial tensile testing; and complex geometric shapes such as turbine prototype blades with e) internal cooling channels or f) thin overhanging platforms. Credit: College of Engineering

In recent years, it has become possible to use laser beams and electron beams to "print" complex engineering objects that cannot be achieved with conventional manufacturing. The additive manufacturing (AM) process, or three - dimensional printing of metallic materials, involves melting and fusing small powder particles - each about 10 times smaller than a sand grain from a beach-in submillimeter "puddles" created by focusing a laser or electron beam on the material.

"Focused beams provide precise control, allowing you to "tune" properties in critical locations of a printed object, " said Tresa Pollock, Professor of materials and associate Dean of the College of engineering at the University of California, Santa Barbara. "Unfortunately, many modern metal alloys used in extremely heat-intensive and chemically aggressive environments found in energy, space, and nuclear engineering are incompatible with the AM process."

The challenge of discovering new AM-compatible materials was overwhelming for Pollock, a world-renowned scientist who conducts research on modern metal materials and coatings. "This was interesting," she said , "because a set of well-compatible alloys can transform the production of metal materials that have high economic value, i.e. materials that are expensive because their constituents are relatively rare in the earth's crust," allowing the production of geometrically complex structures with minimal material waste.

"Most high - strength alloys that work under extreme conditions can't be printed because they crack," continued Pollock, Alcoa distinguished Professor of materials science. "They may crack in the liquid state while the object is still being printed, or in the solid state after the material has been extracted and subjected to some heat treatment. This prevents people from using alloys that we currently use in applications such as aircraft engines to print new developments that can, for example, significantly increase productivity or energy efficiency."

Now, in an article in the journal Nature Communications, Pollock collaborated with Carpenter Technologies, Oak Ridge National Laboratory, UCSB staff scientists Chris Torbet and Gareth Seward, and a UCSB Ph. D. students Sean Murray, Kira push, and Andrew Polonsky describe a new class of superalloys that overcome this cracking problem and therefore have huge prospects for advancing the use of AM to produce complex single-use components for use in high-load and high-load environments. execution environment.

The research was supported by a $ 3 million Vannevar Bush faculty fellowship (VBFF) that Pollock received from the U.S. Department of defense in 2017. The VBFF is the Department of defense's most prestigious award for individual researchers, supporting basic research that can have a transformative impact.

In this paper, the authors describe a new class of high-strength, defect-resistant, 3D-printable superalloys, defined as typically Nickel-based alloys that maintain material integrity at temperatures up to 90% of their melting point. Most alloys break down at a melting point of 50%. These new superalloys contain approximately equal parts of cobalt (Co) and Nickel (Ni), as well as fewer other elements. These materials are suitable for three-dimensional crack-free printing using electron beam melting (EBM), as well as for more complex laser powder printing methods, which makes them widely useful for the many printing machines that are entering the market.

Because of their excellent mechanical properties at elevated temperatures, Nickel-based superalloys are the preferred material for structural elements such as single-crystal (SX) turbine blades and blades used in hot parts of aircraft engines. In one of the superalloy variants that the team developed, Pollock said: "The high percentage of cobalt allowed us to develop elements in the liquid and solid States of the alloy, making it compatible with a wide range of printing conditions."

The development of the new alloy was facilitated by previous work done through NSF-funded projects aligned with the national materials genome initiative, whose main goal is to support research to address the serious challenges facing society by developing advanced materials "at twice the speed, half the cost ".

Pollock's NSF work in this area was conducted in collaboration with fellow UCSB materials professors Carlos G. levy and Anton van der Ven. Their efforts included the development and integration of a Suite of computational and high-performance alloy design tools needed to investigate the large volume of multicomponent composition needed to discover new alloys . In discussing the new paper, Pollock also acknowledged the important role of the collaborative research environment in the College of Engineering that made this work possible.

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