Life Sciences

Image title: Designing 3D bicontinuous metal–intermetallic composites via dealloying-alloying process

Image caption: Researchers developed a new two-step technique for the fabrication of metal–intermetallic composites with 3D interconnected structures by first producing a porous Ti matrix via liquid metal dealloying followed by immersion in Mg–3Al metal melt. The obtained three-phase composite exhibited excellent hardness and strength.

Image credit: The authors

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Metal alloys are a gift to mankind. They enable us to create strong, lightweight airplanes and shiny metal knives that resist rust even after regular exposure to water. Certainly, at times, targeted dealloying of certain alloys is necessary to achieve particular objectives. A commonly used method for dealloying, or selective leaching, involves using chemicals to remove specific components of a precursor alloy. This chemical dealloying process typically uses an acidic solution in which the less noble metal dissolves, leaving behind the more noble metal and a 3D interconnected porous material. However, this process is typically applicable only to noble metals like gold, silver, and platinum, and cannot be extended to other metals.

For alloys made up of non-noble metals, the liquid metal dealloying or LMD process appears to be a suitable option. This process uses a metallic melt instead of an aqueous solution for selective leaching of components. The 3D interconnected non-noble metal-metal composites obtained via this procedure have shown great physical properties. Despite the promising applications of LMD not much is known about the complex reactions that occur between the metallic melt and the elements of the precursor alloy. Also, most non-noble metal-metal composites experience separation due to weak bonding between the different metal matrices, significantly reducing their strength and making practical application difficult. 

A recent breakthrough by a research team from South Korea, led by Professor Sung Hyuk Park from Kyungpook National University, offers a solution to these challenges. They introduced an innovative two-step process for fabricating metal–intermetallic composites with a 3D bicontinuous structure, utilizing LMD followed by subsequent alloying. The research was published in the Journal of Magnesium and Alloys on November 02, 2023.

"In a single-step LMD process, the atoms can quickly react with the metal being alloyed or added to the composite system, significantly hindering dealloying. This interference can reduce the dealloying rate and result in an inhomogeneous microstructure. Conversely, by dividing the process into two steps, first, dealloying, followed by alloying we can enhance both the dealloying rate and efficiency," stated Prof. Park highlighting the reason behind their selected fabrication approach. 

To create the 3D bicontinuous structure, the team first made porous Ti structures using LMD, then soaked them in molten Mg–3Al (wt%) metal. They found that as immersion time increased, so did the concentration of Al in the Ti matrix. This unusual increase in the Ti matrix area fraction with immersion time is likely due to Al's better mixing with Ti than with Mg. This led to a sequential phase transition in the Ti matrix: α-Ti → Ti3Al → TiAl, significantly impacting the material's hardness and strength. The resulting three-phase composite, Mg–Ti3 Al–TiAl, showed higher compressive strength and hardness than conventional Mg–Ti composite. Despite containing brittle phases, it also exhibited great fracture resistance.

This new technique for obtaining 3D bicontinuous structures can act as a guideline for additional alloying in the case of 3D interconnected structures that underwent LMD or 3D printed materials.  The findings from this process can be used to design tough intermetallic composites for use in the automotive industry, sports equipment and medical device manufacturing, aerospace industry and beyond. "Development and application of 3D bicontinuous structure metal–intermetallic composites through LMD processes are poised to have the potential to drive significant technological, environmental, and economic advancements. By improving the performance and sustainability of various applications our work can positively impact people's lives in numerous ways over the next decade," concluded Prof. Park.

Reference

About the Institute

Kyungpook National University (KNU) is a national university located in Daegu, South Korea.

Founded in 1946, it is committed to becoming a leading global university based on its proud and lasting tradition of truth, pride, and service. As a comprehensive national university representing the regions of Daegu and Gyeongbuk Province, KNU has been striving to lead Korea’s national and international development by fostering talented graduates who can serve as global community leaders.

Website: https://en.knu.ac.kr/main/main.htm

About the author

Sung Hyuk Park is a Professor in the Department of Materials Science and Metallurgical Engineering at Kyungpook National University, a position he has held since 2016. He earned his Ph.D. under the supervision of Professor Chong-Soo Lee at POSTECH. Prior to joining Kyungpook National University, Prof. Park served as a Senior Researcher at the Korea Institute of Materials Science from 2011 to 2016. His research interests encompass various areas including lightweight magnesium alloys, metal-metal hybrid materials, plastic deformation, twinning behavior, and fatigue properties of metallic materials such as magnesium, aluminum, titanium, nickel alloys, and steels. Prof. Park is actively involved in editorial boards, serving on journals like the Journal of Magnesium and Alloys, Korean Journal of Metals and Materials, Metals, and Materials International.

Website: https://www.shparklab.com/professor