Production of materials saturated with twin boundaries by compacting electrolytic microparticles

Abstract

The creation of new materials with unusual proper ties, which are determined by the "technology (tech nique) structure properties" chain, is one of the challenging problems in physics and engineering. In particular, compacting (pressing) small metallic particles is one of the methods for producing new functional and nanostructured materials [1]. The choice of the structure of small metallic particles for the subsequent production of a compound determines its structure and, hence, properties.From this standpoint, a twin boundary is of partic ular interest as a planar lattice defect and a structural element of a small particle, since it can impart unique properties to a micro object. For example, a high con centration of twin boundaries in electrodeposited metals increases their thermal stability and micro hardness and decreases their plasticity [2]. When a metal exhibiting a superconducting transition has a twin boundary, specific conditions for Cooper pairing, which are favorable near a twin boundary as compared to the volume, can appear near this boundary [3]. Cor respondingly, the superconducting transition temper ature in the twinning plane can be higher than this temperature in the crystal structure around the twin boundary [3].Therefore, the purpose of this work is to propose a technique for producing nanostructured materials sat urated by twin boundaries using the compacting of small electrolytic particles as an example.As the microparticles forming the basis of a future compound, we chose small metallic copper electrode posited particles. A technique for the formation of small metallic copper particles with a given structure has been developed and tested [4]. Experimental investigations demonstrate that small particles with pentagonal symmetry are the main carrier of twin boundaries. According to the classification in [5], they have the following three basic habits: small decahedral particles (Fig. 1a), needle like particles (Fig. 1b), and small icosahedral particles (Fig. 1c).Particles of the first two types have one fivefold symmetry axis and five twin boundaries. The third type of particles, namely, small icosahedral particles, have six fivefold symmetry axes and 30 twin boundaries per particle [5]. Small icosahedral particles consist of 20 weakly distorted single crystal tetrahedral regions, and each tetrahedron is a close packed element of the fcc structure. Tetrahedra connect with each other along {111} boundaries, which transform into twin boundaries inside a small particle [5]. Obviously, these small icosahedral particles are the best candidates for compacting followed by the formation of a material saturated by twin boundaries.The choice of the electrodeposition parameters that results in predominant formation of small icosa hedral particles was a challenging problem, and we solved this problem using the trial and error method. As was shown theoretically [6] and experimentally [7][8][9], the structure, the size, and the scenario of the development of crystalline aggregates depend on the heat and m...