Evolution of a bicontinuous structure in peritectic melting: The simplest form of dealloying

Abstract

Materials with two interpenetrating phases often exhibit excellent mechanical and physical properties, and can be used as precursors for the production of porous materials that have many practical applications. Such bicontinuous structures can be generated by liquid metal dealloying, followed by quenching. However, this procedure is neither efficient nor cost-effective, because it requires a sizeable liquid-metal corrosion reservoir and long-range mass transport that restricts sample size and synthesis rate. In this paper, we propose a mechanism that generates bicontinuous structures by simple thermal treatments. By heating a TiAg intermetallic compound to above its peritectic temperature, we demonstrate that it decomposes into solid Ti and liquid Ag that interpenetrate at the micrometer scale. The resulting structure can be quenched to room temperature. In this case, peritectic melting proceeds by cooperative growth of solid Ti and liquid Ag into a solid TiAg compound. The behavior of structural evolution resembles the process of dealloying, particularly liquid metal dealloying, except that corrosion media and long-range diffusion are no longer required. Our findings suggest that the directional transition from a solid to another solid and a fluid phase, instead of ``selective etching,'' might be responsible for the evolution of a bicontinuous structure in all dealloying processes. This study also provides a versatile metallurgical route to generate bicontinuous solid/solid or solid/liquid structures and hierarchical nanoporous structures in many materials for mechanical and functional applications.