Preparation, Mechanical Properties And Electronic Structure Of Ductile Rare-earth Intermetallic Compounds

Stoichiometric intermetallic compounds have always been touted for their excellentchemical, physical, electrical, magnetic properties than normal metals; in additionintermetallic compounds have strong bonding between atoms, high melting point, whichare still able to keeping high strength at high temperature, while having excellent creepresistance and oxidation resistance, they are new structure materials at high temperaturewith enormous potential, but few practical uses have materialized because they are brittleat room temperature. This dissertation we studied up on a family of fully ordered,stoichiometric binary rare-earth intermetallic compounds (RM) with high ductility at roomtemperature. Although conventional wisdom calls for special conditions, such asnon-stoichiometry, metastable disorder or doping to achieve some ductility in intermetalliccompounds at room temperature, none of these is required in these unique B2 rare-earthcompounds. On account of RM exhibit high ductilities at ambient temperature under noneimproving measure was taken, so RM not only have tremendous application foreground,but also offer new insights into studying the origin of brittleness at room temperature ofother intermetallic compounds.The preparation, mechanical properties and electronic structure of binary ductilerare-earth intermetallic compounds were studied in this dissertation. Firstly, thestoichiometric binary ductile rare-earth intermetallic compounds were preparedsuccessfully by cold crucible levitation melting (CCLM), and they were characterized byX-ray. Secondly, the prepared specimens were tested in compression and in tension, thefracture surfaces were analyzed by SEM, the results of tests and analysis indicated that RMhad obvious ductility at room temperature, the tensile elongation of polycrystalline DyCuwas larger than polycrystalline YCu at the same tensile strain rate, and the tensileproperties of polycrystalline YCu at room temperature were sensitive to the tensile strainrate with abnormal behavior. For a better understanding of the unusual ductility of RM atthe room temperature, the electronic structure of YCu, DyCu and YAg which are on behalfof RM were studied by full-potential linearized augmented plane wave method (FP_LAPW)on the basis of the density functional theory (DFT). The calculations of YCu and YAg weretreated using the generalized gradient approximation (GGA), while DyCu was treatedusing LDA+U. Firstly, the YCu with B27 structure is more stable than B2 structure at lowtemperature, which was analyzed from the total energy, the energy of formation, density of states and electronic band structure. Secondly, the calculations of DyCu using LDA+Uwere detailed discussed. The last, the electronic structures and elastic constants of YCu,DyCu and YAg were compared. The mechanism of RM with high ductility at roomtemperature was innovatively detailed analyzed from the electronic structure aspec, andproviding the reliable evidence for the unusual ductility at room temperature.