Zhang Kunhua

First-principles Study on Structure and Hardness of the RuB2

Abstract The first-principles were employed investigate the structure properties, elastic constant and electronic structure of two phases of the RuB 2 (orthorhombic and hexagonal phase). The lattice parameter and volume of the two RuB 2 phases are in good agreement with experimental values. The calculated elastic constants indicate that the RuB 2 exhibits excellent mechanical properties. The electronic structure shows that hybridization occurs between Ru (d states) and B (p states) and form Ru-B covalent bonding forms. The results reveal that the hexagonal RuB 2 is a stable phase at ground state.

Micro-Superplastic Behavior of Copper Oxide in AgCuO Composites

Abstract In the investigation of AgCuO composites, we have found a type of copper oxide particles with a superplastic deformability behavior, which is similar to that of metals. To find the reason of the deformability of the copper oxide particles. SCM, STEM and TEM were used to analyze their crystal structures in AgCuO composites, The results show that the copper oxide particles with micro-superplasticity in the composites have cubic crystal structure, and their maximum elongation can be up to 300%, The copper oxide particles with no micro-superplasticity in the composites have monoclinic crystal structure. But the micro-superplastic behavior and mechanism of the copper oxides with the cubic crystal structure are not clear for the time being, the further investigation could be needed.

Investigation of Internal Oxidation on Pt-Ir-Zr High-Temperature Alloy

Abstract An internal oxidation method was applied to investigate the dispersion-strengthening of Pt-Ir-Zr alloy, and the thermodynamic condition was explored for this alloy. Scanning electron microscopy (SEM) was employed to analyze the internal oxidation morphologies. Combining with tensile strength, the optimal internal oxidation time was determined. The results show that oxidation of Ir and Zr will occur under the experimental condition, and the oxygen pressure of Zr is lower than that of Ir. The grain size of the alloy increases with the prolonging of time and remains stable when the oxidation time is up to 40 h. The tensile strength decreases exponentially with the increase of oxidation time. The time for optimal internal oxidation is 40 h at 1100 °C.

The High Temperature Creep Behavior of Dispersion Strengthened Pt5Rh Composite

Abstract Adopting a large plastic deformation process, the dispersion strengthened Pt5Rh composite was prepared. The microstructure of the composite was analyzed by SEM, and the high temperature creep tests were carried out by a self-made high temperature creep test facility. The experiment results show that at high temperature and under low load the stress exponent of the dispersion strengthened Pt5Rh alloy does not change obviously with increasing of the temperature, and its apparent activation energy is much higher than those of pure platinum and Pt10Rh alloy. The high temperature creep properties of the dispersion strengthened Pt5Rh are better than those of conventional alloys. The creep mechanism of the dispersion strengthened Pt5Rh belongs to the proliferation creep mechanism; the creep fracture at high temperatures presents the brittle fracture.

First Principle Study on the Interface of Ag-Ni Composites

Abstract The interface combinations between Ag(110), (211) and Ni(110), (211) were studied by the first-principle based on the density functional theory calculations. The interface bonding energy, charge population and electronic structure were investigated. It is found that among all the combinations the interface bonding energy and electron hybridization reach the maximum values at Ag(100)-Ni(211) interface, and this interface combination is the most stable.

Strain Strengthening of Ag-10Cu in situ Filamentary Composite Prepared by Heavy Deformation

Abstract Ag-10Cu in situ filamentary composite was prepared by hot extrusion and cold wire drawing. The as-cast and as-extruded Ag-10Cu alloys consist of Ag matrix, (Ag+Cu) eutectic and Cu precipitates which will become a structure of Ag matrix and Cu filaments after heavy deformation. The size of Cu filaments, transformed from coarse Cu precipitates, changes with drawing strain, and their relationship can be expressed as d = d o exp(−0.144 η ). Two-stage strengthening characteristics were obtained and the strengthening mechanism of this composite was discussed. A combination of ultimate tensile strength approaching 1 GPa and electrical conductivity exceeding 60% IACS can be achieved for this composite. The effect of intermediate heat treatment was also discussed.

Effect of Cumulative Severe Plastic Deformation on Microstructure and Properties of Ag-CeO2 Composites by RSP

Abstract In present study, Ag-CeO2 composites were prepared by reaction synthesis processing. The phases, the procedure of microstructure homogenization, and the microstructure and physical property evolution of the Ag-CeO2 composites via the severe plastic deformation were researched extensively. XRD, SEM and EDS analysis indicate that the Ag-CeO2 composites with tiny AgCeO2 clusters forming in the Ag matrix can be obtained by reactive synthesis processing, and the microstructure shows the tiny CeO2 clusters distribute in the Ag matrix which becomes homogenous and dispersed after cumulative severe plastic deformation. The tensile strength and electrical resistivity decrease with the increase of true strain, while the elongation changes contrarily.