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Using 3D printing to combine parts made of two different alloys could make metal turbine blades stronger.

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When two are stronger than one

10 Jun 2021

New research shows that titanium alloys joined by 3D-printed curved interlayers are stronger and less likely to crack.

Whether you are flying 15,349 kilometers between Singapore and New York or just taking a short hop over to Kuala Lumpur, the journey of a thousand miles begins with a single turbine blade. Hidden in the jet engines tucked under the wing of every passenger plane, turbine blades are a marvel of modern engineering, designed to withstand the extreme heat and stress that enables flight. Leading industry players such as GE and Siemens have been exploring the use of 3D printing to make metal turbine blades better, but finding the right alloy for the job can be challenging.

Strong, lightweight and heat resistant, gamma titanium alloys like Ti–48Al–2Cr–2Nb are ideal for constructing high-temperature alloy components for aerospace applications—in theory. In practice, it is brittle and difficult to machine at room temperature due to its high aluminum content. On the other hand, a low aluminum content alloy called Ti–6Al–4V can be easily fabricated into any shape, but doesn’t have all the desirable qualities of Ti–48Al–2Cr–2Nb.

“We wanted to combine the advantages of the two alloys for the best of both worlds,” said Pan Wang, a Scientist at A*STAR’s Singapore Institute of Manufacturing Technology (SIMTech). To achieve this, the team started with a Ti–6Al–4V base, using a 3D-printing method called electron beam melting (EBM) to create a prototype turbine blade made of Ti–48Al–2Cr–2Nb on top. “We creatively produced a 3D-specific interlayer surface to enhance the bonding in an in situ way,” he said.

By using different printing strategies, the team was able to create two different interfaces between Ti–48Al–2Cr–2Nb and Ti–6Al–4V, one straight and one curved in shape. To test the strength of the resulting bimetal components, the researchers pulled the joined pieces apart, recording the force needed and studying the resulting cracks. As predicted, the EBM-formed curved bimetal component was stronger than alloys joined using other methods, achieving a tensile strength of 389 MPa.

Studying the fracture patterns within the interlayer—an intermediate region between the two different materials—further revealed that curved interlayers were thicker, had a larger surface area and contained higher levels of titanium solid solution, all of which enhanced strength. “The secret behind this strength is the design of 3D-specific interlayer,” Wang said.

Interestingly, the researchers found that the curved interlayer blocked the propagation of primary cracks because they encountered the stronger Ti–6Al–4V. This either changes the crack direction or prevents it from propagating. “Consequently, extra tensile loading was needed to form the new cracks and thus the strength was increased,” Wang explained.

The researchers are testing the mechanical performance of their novel bimetal component under high temperatures to qualify it for use in aerospace applications. To further improve the methodology, Wang said that future work could focus on accelerating the design of the interface by machine learning and suppressing the formation of a detrimental phase by calculated phase diagrams.

The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology (SIMTech).

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References

Zhai, W.G., Wang, P., Ng, F.L., Zhou, W., Nai, S.M.L., et al. Hybrid manufacturing of γ-TiAl and Ti–6Al–4V bimetal component with enhanced strength using electron beam melting. Composites Part B: Engineering 207, 108587 (2021) | article

About the Researcher

Pan Wang is a Scientist II in the Metal & Ceramic Forming Group at A*STAR’s Singapore Institute of Manufacturing Technology (SIMTech). He leads the development of electron beam melting (EBM) process from fundamental research to industrial applications. His research covers the development of high-performance metallic powders for additive manufacturing; design and optimization of new structures for additive manufacturing; promotion of additive manufacturing technology to the industry by overcoming the shortcomings of current technology; and phase transformation and deformation behavior of metastable alloys.

This article was made for A*STAR Research by Wildtype Media Group