Korea Maritime and Ocean University scholars find key to reducing defects in multimaterials

Materials used in the fields of aerospace, automobiles, medical equipment, defense need to withstand extremely harsh environments. Small flaws in the materials, i.e. cracks, can lead to catastrophic consequences and massive economic loss. However, most materials cannot handle such high temperatures and pressures. Multimaterials, like functionally graded materials (FGMs), which combine different materials to produce improved performance, are ideal in this situation.

Multimaterials are normally made by additive manufacturing (AM), where layers of different materials are deposited one over the other. However, cracks and pores are common at the boundary layers due to the different properties of the materials. FGMs seek to reduce these cracks by creating a ‘gradient’ to the composition change across the volume of the material. Now, researchers from Korea Maritime and Ocean University have developed a way to synthesize a high-performance FGM made of Inconel 718 and stainless steel (STS) 316L and minimize its defects. According to Professor Do-Sik Shim, who led the study, “Inconel 718 has excellent properties, but it is expensive. By mixing it with STS 316L to create a high-performance FGM, we have not only improved its technical and commercial advantages, but its economic feasibility as well.” Their findings are published in Journal of Materials Research and Technology.

For their work, the research team deposited STS 316L onto Inconel 718 using a 3D-printing technique called ‘directed energy deposition.’ They created three types of FGMs, non-graded (NG), which involved a layer of STS deposited directly on Inconel, graded (10), and graded (25), which had mixing gradients of 10% and 25% respectively. They found that interfacial cracks were common in the NG type, whereas Graded (10) and Graded (25) had cracks only in specific regions due to ‘columnar-to-equitaxial transition’ (a transition in the microstructure of the FGM), precipitation, or the inclusion of titanium, aluminium or chromium impurities. They moreover saw that the Graded (25) type showed the highest tensile strength and elongation.

These findings indicate that the microstructure and mechanical properties of FGM are highly dependent upon the gradient ratio of the components, thereby creating the potential to achieve minimal or even no defects in FGMs. “These findings will lead to improvements in the field, such as reduced costs, extended component lifespans in equipment, and enhanced functionality,” says Professor Shim. The research team’s future plans include using the new FGM to manufacture complex shaped parts using AM technologies.

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Reference

DOI: https://doi.org/10.1016/j.jmrt.2022.01.029

Authors:

Seung Weon Yang ^a,b, Jongcheon Yoon b, Hyub Lee ^b,**, Do Sik Shim ^c,*

Affiliations:

^a Department of Materials Science & Engineering, Yonsei University, Republic of Korea

^b Advanced Joining and Additive Manufacturing R&D Department, Korea Institute of Industrial Technology, Republic of Korea

^c Department of Ocean Advanced Materials Convergence Engineering, Korea Maritime and Ocean University, Republic of Korea

About National Korea Maritime & Ocean University 

South Korea’s most prestigious university for maritime studies, transportation science and engineering, the National Korea Maritime & Ocean University is located on an island in Busan. The university was established in 1945 and since then has merged with other universities to currently being the only post-secondary institution that specializes in maritime sciences and engineering. It has four colleges that offer both undergraduate and graduate courses.  

Website: http://www.kmou.ac.kr/english/main.do

About the author

Dr. Do-Sik Shim received a Ph.D. in Mechanical Engineering from KAIST, Korea, in 2010. He has been an associate professor at the Korea Maritime and Ocean University since 2017. His research interests include additive manufacturing (AM), sheet metal forming, finite element simulations, as well as optimal design. Over the last few years, his group has been actively researching metal AM techniques, such as directed energy deposition and powder bed fusion, in terms of process design, mechanical and metallurgical characteristics, and industrial applications.