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Crack-Resistant Superalloys Hold Promise for AM of High-Stress Components

Thursday, December 10, 2020
 

Researchers have identified a new class of superalloys that reportedly hold promise for advancing the use of additive manufacturing (AM) to produce complex one-off components for use in high-stress, high-performance environments, reports Physics.org. Previously, many alloys for such applications could not be printed due to cracking issues.

“A suite of highly compatible alloys could transform the production of metallic materials having high economic value—i.e., materials that are expensive because their constituents are relatively rare within the earth's crust—by enabling the manufacture of geometrically complex designs with minimal material waste,” explains Tresa Pollock, Alcoa Distinguished Professor of Materials and associate dean of the College of Engineering at UC Santa Barbara, to Physics.org. "Most very-high-strength alloys that function in extreme environments cannot be printed, because they crack. They can crack in their liquid state, when an object is still being printed, or in the solid state, after the material is taken out and given some thermal treatments. This has prevented people from employing alloys that we use currently in applications such as aircraft engines to print new designs that could, for example, drastically increase performance or energy efficiency."

Now, in an article in the journal Nature Communications, Pollock, in collaboration with Carpenter Technologies, Oak Ridge National Laboratory, UCSB staff scientists Chris Torbet and Gareth Seward, and UCSB Ph.D. students Sean Murray, Kira Pusch and Andrew Polonsky, describes a new class of superalloys that overcome this cracking problem.

The research was supported by a $3 million Vannevar Bush Faculty Fellowship (VBFF) awarded to Pollock from the U.S. Department of Defense in 2017. The VBFF supports basic research that could have a transformative impact.

In the Nature Communications article, the authors describe a new class of high-strength, defect-resistant, 3D-printable superalloys, defined as typically nickel-based alloys that maintain their material integrity at temperatures to 90 percent of their melting points, whereas most alloys fall apart at the 50-percent level. The new superalloys contain approximately equal parts cobalt and nickel, plus smaller amounts of other elements. They are amenable to crack-free AM via electron beam melting as well as the more challenging laser-powder-bed approaches, making them broadly useful for printing machines on the market.

Due to excellent mechanical properties at elevated temperatures, nickel-based superalloys are the material of choice for structural components such as single-crystal turbine blades and vanes used in the hot sections of aircraft engines. In one variation of a superalloy that the team developed, "the high percentage of cobalt allowed us to design features into the liquid and solid states of the alloy that make it compatible with a wide range of printing conditions," Pollock says.

The development of the new alloy was facilitated by previous work done as part of National Science Foundation (NSF)-funded projects aligned with the national Materials Genome Initiative, which has the underlying goal of supporting research to address grand challenges confronting society by developing advanced materials ‘twice as fast at half the cost.’

Pollock's NSF work in this area was conducted in collaboration with fellow UCSB materials professors Carlos G. Levi and Anton Van der Ven. Their efforts involved developing and integrating a suite of computational and high-throughput alloy design tools needed to explore the large multicomponent composition space required to discover new alloys. 

 

See also: Carpenter Technology


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