New crack-resistant 'superalloys' compatible with AM
US scientists have developed a new class of ‘superalloy’ that overcomes the cracking issues currently faced when using high-strength alloys in additive manufacturing (AM).
In Nature Communications, the researchers say that these superalloys hold tremendous promise for advancing the use of AM to produce complex one-off components for high-stress, high-performance environments, such as aircraft engines.
Currently, many advanced metallic alloys used in extreme heat-intensive and chemically corrosive environments in the energy, space and nuclear sectors are not compatible with AM.
‘Most very-high-strength alloys that function in extreme environments cannot be printed, because they crack,’ explained Tresa Pollock, a professor of materials at the College of Engineering at UC Santa Barbara and an author on the paper. ‘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 issue has prevented alloys currently used in extreme environments from being printed into new designs that could dramatically increase performance and energy efficiency.
In collaboration with Carpenter Technologies and Oak Ridge National Laboratory, Pollock and her colleagues have therefore developed a new class of superalloy that overcomes this cracking problem.
In the Nature Communications paper, the researchers demonstrate that the superalloys are high-strength, defect-resistant and most importantly, 3D-printable. They are typically defined as nickel-based alloys that maintain material integrity at temperatures up to 90 per cent of their melting point. This is significant, as most alloys tend to fall apart at 50 per cent of their melting point.
The superalloys contain approximately equal parts cobalt and nickel, plus smaller amounts of other elements. The materials are amenable to crack-free 3D printing via laser powder bed fusion and electron beam melting, making them compatible with many printers currently on the market.
‘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,’ commented Pollock.
Because of their excellent mechanical properties at elevated temperatures, the researchers emphasise that their nickel-based superalloys could be the material of choice for structural components such as single-crystal turbine blades and vanes used in the hot sections of aircraft engines.