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First-principles Pd-Ru-Zr alloy system with the structure and stability of Calculation

Author: HuJieQiong
Tutor: XieMing
School: Kunming Institute of Precious Metals
Course: Materials Science
Keywords: First-principle Pd-Ru-Zr alloy Solid solutions Elastic properties Electronic structure
CLC: TG131
Type: Master's thesis
Year: 2012
Downloads: 152
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Abstract


Precious metals alloy are the important materials for aviation industry, aerospaceindustry, shipbuilding industry, electronic industry, chemical industry and military industry.The further research on the structures and phase properties will be beneficial to improve thebasic research system of precious metals alloy and provide theoretical support to theirapplication. With the progress in computer technology and numerical methods,first-principles calculations based on density functional theory have become a powerful toolfor the investigation of material property. The first-principles calculation of the phasestability and mechanical property of materials has matured considerably. In this dissertation,the phase stability and mechanical property of representative precious alloy system of Pd-Rudoped Zr are investigated theoretically by first-principles method. The concerned propertiesinclude site occupancy, phase stability, elastic property and ideal strength. The aboveresearches give an important theoretical basis for the optimum design of Pd-Ru-Zr rare andprecious metals alloy materials.In this dissertation, the cohesive energy, charge population and electronic structure ofPd-Zr and Ru-Zr binary alloys are studied by first-principles calculations. The results showthat the enthalpy of formation and cohesive energy of Pd-Zr alloys are lower than Ru-Zralloys, which indicated that Zr could react with Pd to form the stable compound when dopeda little Zr into Pd-Ru solid solutions, and the phase stability of Ru-Zr alloys is better thanPd-Zr alloys. According to the analysis of charge population, the number of electronictransfer between Pd and Zr is more than Ru and Zr, which indicated that Zr could easilyreact with Pd to form the stable compound.The cohesive energy, bond length, charge population and electronic structure ofRu1-xPdxZr、Pd1-xRuxZr1/2and Pd1-xRuxZr1/3solid solutions are studied by first-principlescalculations. The results show that the total energies of cubic Ru1-xPdxZr solid solutionsincrease monotonously with increasing the contents of Pd element, while the cohesiveenergies of Ru1-xPdxZr decrease monotonously with an increase of Pd content. According tothe analysis of demixing energy of Ru1-xPdxZr, Ru2Pd6Zr8is stable than another phases, sothe bond length, electron charge density distributions and electronic structure of two structure of Ru2Pd6Zr8are studied. The results show that Ortho-Ru2Pd6Zr8is more stablethan Cubic-Ru2Pd6Zr8. The total energies of tetragonal Pd1-xRuxZr1/2solid solutions increasemonotonously with increasing the contents of Ru element, and the cohesive energies ofPd1-xRuxZr1/2also increase monotonously with an increase of Ru content. According to theanalysis of demixing energy of Pd1-xRuxZr1/2, Pd3RuZr2、Pd2Ru2Zr2、PdRu3Zr2are unstable,so the bond length, charge population and electronic structure of these phases are studied.The results show that Pd3RuZr2is more stable than another two phases. The total energies ofhexagonal Pd1-xRuxZr1/3solid solutions increase monotonously with increasing the contentsof Ru element, and the cohesive energies of Pd1-xRuxZr1/3also increase monotonously withan increase of Ru content. According to the analysis of demixing energy of Pd1-xRuxZr1/3,Pd11RuZr4、Pd8Ru4Zr4、Pd5Ru7Zr4、Pd2Ru10Zr4are stable than another phases, so the bondlength, charge population and electronic structure of these phases are studied. The resultsshow that Pd11RuZr4is more stable than other phases.The cohesive energy, charge population, bond length and elastic properties of orderedand disordered Pd-Ru-Zr solid solutions are studied by first-principles calculations. InPd-Ru-Zr ordered solid solutions, two solid sulitions which Ru and Zr occupy the top angleare more stable than the solid solution which Pd occupy the top angle of the lattice. InPd-Ru-Zr disordered supercell solid solutions, the phase stability of Pd-Ru-Zr disorderedsystem can be enhanced by adding Ru and Zr into this system, where Pd-5Ru-5Zr is morestable than other solid solutions in Pd-5Ru system, Pd-10Ru-5Zr is more stable than othersolid solutions in Pd-10Ru system, and Pd-10Ru is more stable than Pd-5Ru. In Pd-Ru-Zrvirtual crystal approximation models, the elastic constant calculations can determine thestability of phases and some mechanical properties of materials. According to the analysis ofelastic stability criteria, Pd-5Ru-5Zr is more stable in Pd-5Ru system, and the phase stabilityof Pd-10Ru system decreased by adding Zr into the system, so Pd-10Ru is more stable inPd-10Ru system. To prove the accuracy of theoretical calculation, in this dissertationexperiment tested the elastic modulus and mechanical properties of different percentage ofPd-Ru-Zr system. Experimental results show that the materials plastic measuring is accordwith theoretical calculation and the test data of elastic modulus are agree well with theresults by theoretical calculation, but the test data of elastic modulus deviate unavoidablyfrom the theoretical calculation results on the change trend of elastic modulus.

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