Liquid Metal Dealloying

Guest Speaker： Professor Hidemi Kato, Vice president of the Japan Institute of Metals and Materials (JIMM), Tohoku University, Japan

Inviter: Prof. Guangyin Yuan

Date&Time: Wednesday, 4.Dec., 10:00-11:00

Venue: Meeting Room 308, Xu Zuyao Building

Biography:

Dr. Hidemi Kato is a professor at the Institute for Materials Research (IMR), Tohoku University and currently the vice president of the Japan Institute of Metals and Materials (JIMM). Kato is a metallurgist and has many achievements in the development and basic research on non-equilibrium metallic materials such as amorphous alloys and bulk metallic glasses (BMGs), as well as in high-entropy alloys (HEAs). In 2010, His research group invented Liquid Metal Dealloying (LMD) during researching BMG composites, a metallurgical dealloying method using metallic liquids as a medium, which has successfully attracted much attention for its wide range of research fields, including functional porous materials, bi-continuous composites with immiscible elements and its application to dissimilar materials joining.

Abstract:

Nanoporous metals have drawn considerable attention for their highly functional properties due to its unique 3D open cell structures. They are usually produced by selective dissolution of elements from a multicomponent alloy (known as the dealloying method in aqueous solutions). Thus, the corrosion or etching is the mechanism of the dealloying technique. This method is based on differences in the electrode potential of each element present in the alloy, therefore, porous structure can be mainly obtained for noble metals of which potential is higher than the standard hydrogen electrode.

In this paper, Liquid Metal Dealloying (LMD), an alternative dealloying technique for developing porous structure even in the base and half metals having low electrode potential is newly introduced. The molten metal is employed in place of the acid/alkali aqueous solutions for the dealloying process. The chemical interaction among the elements indicated by the mixing enthalpy is the dominant factor as the same as the standard electrode potential of the metals in the aqueous solution. For example, strong attractive interaction between Mg and Cu, and strong repulsive interaction between Mg and Ti at elevated temperature enable us to perform dissolving Cu from Ti-Cu solid alloy in the Mg melt, which resulted in the formation of a hcp-Ti/hcp-Mg bi-continuous nano/micro composite. This immiscible composite is a new type of composite material, which shows excellent tensile strength and ductility despite the hcp nature of both elements, as well as a low apparent Young’s modulus maybe due to the weak interfacial bonding force between Ti and Mg. Forming this composite at the interface between bulk Ti and Mg, the strong dissimilar joining of immiscible Ti and Mg has been also succeeded. In many acid solutions, pure Ti is passive, while Mg is highly active. This great difference in corrosion behavior enables selective removal of hcp-Mg from the hcp-Ti/hcp-Mg composite, resulting in the open nano/micrometer porous Ti metal (If etching Ti parts by a HF aq. solution, nanoporous Mg can be obtained). Using LMD, porous metals of Zr, V, Nb, Ta, Cr, Mo, W, Fe, C(graphite), Si and alloys, β-Ti, Fe-Cr, Ni-Cr etc. have been successfully prepared. Porous structure in various base metals can be applied for active materials and catalysts for energy devices.