Yuan Hua Lin

Correlation between hardness and pressure of CrB4

The correlation between hardness and pressure for two different structures of CrB4 is investigated by a first-principles approach. With increasing pressure, the hardness gradually decreases, in contrast to the bulk modulus, shear modulus, Youngs modulus and B/G ratio, which monotonically increase. Pressure gives rise to a hardness transition from a superhard to a hard material, which is in good agreement with the experimental data. Moreover, the pressure leads to a brittle-to-ductile transition at 200 GPa based on the analysis of the B/G ratio, which is consistent with the hardness trend. The analysis of the density of states and chemical bonding implies that pressure induces electronic compression and collapse in localized regions, and the variation in hardness originates from the bond reversal between the B–B (3) and B–B (2) covalent bonds, which are located at the applied load plane. Finally, we conclude that the hardness of CrB4 under pressure is related to the B/G ratio and bond characteristics.

Elastic properties and electronic structure of Mo2FeB2 alloyed with Cr, Ni and Mn by first-principles calculations

In this work, we have applied the first-principles calculations to investigate the structural stability, elastic properties and electronic structure of Mo2FeB2 with alloying elements Cr, Ni and Mn. The calculated cohesive energy shows that Cr, Ni and Mn prefer to occupy the Fe atom of Mo2FeB2. However, only when Mn is doped at the Mo atom of Mo2FeB2, it is converted from dynamic unstable state to stable state. The calculated elastic modulus shows that Mo2FeB2 will have better mechanical properties when alloying elements are at Fe site instead of Mo site. Moreover, Cr addition can improve the volume deformation resistance of Mo2FeB2, Mn addition can improve the shear deformation resistance for Mo2FeB2. The calculated B/G ratio shows that Ni addition can improve the brittleness of borides. Furthermore, the hardness of Mo2FeB2 can be enhanced by adding Cr and Mn element. The calculated electronic structure indicates that the increasing of elastic modulus is attributed to the formation of Cr–B and Mn–B covalent bonds.

Thermodynamic Study of Ag-Au-Gd, Tb Ternary Systems

The addition of the rare earth elements into the Ag-based filler alloy, which is typical and important, can control and eliminate the negative effect of impurity elements, and furthermore, it improves the spreading property of the Ag-based filler alloy. Phase diagram provides an important direction for materials design of the Ag-based filler alloy. Thus it is necessary to investigate the phase diagrams and construct the thermodynamic database. On the basis of this background, thermodynamic assessments of the Au-Gd, Tb binary systems were carried out by using the CALPHAD (Calculation of Phase Diagrams) method based on the experimental data including thermodynamic properties and phase equilibrium. The Gibbs free energies of the solution phases were described by sub-regular solution models with the Redlich-Kister equation, while all of the intermetallic compounds were described by sub-lattice models. A consistent set of thermodynamic parameters was derived from describing the Gibbs free energies of each solution phase and intermetallic compound. The calculated phase diagram achieved consistency with the available experiments. Then combined with the assessed relevant binary systems, the Ag-Au-Gd, Tb ternary systems have been predicted. The thermodynamic database of these ternary systems has been developed to present the significant information for the design of Ag-based filler alloys.

Thermodynamic Assessments of the Au-Nd and Au-Dy Systems

The thermodynamic assessments of the Au-Nd and Au-Dy binary systems have been carried out by the Calculation of Phase Diagram (CALPHAD) method based on the available experimental data. The Gibbs free energies of the solution phases including liquid, fcc, bcc, hcp and dhcp were described by the substitutional solution models with the Redlich-Kister equation, and those of the intermetallic compounds were described by the sublattice models. A set of self-consistent and reasonable thermodynamic parameters is obtained for the binary systems, which describes the Gibbs free energies of the solution phases and the intermetallic compounds phases.

Correlation between hardness and bond orientation of vanadium borides

The relationship between hardness and bond characteristic of vanadium borides was investigated by first-principles approach. The calculated lattice parameters of V–B system are in good agreement with previous experimental data. The convex hull indicates that the VB are most stable at ground state. The vanadium borides have higher bulk modulus, shear modulus and Youngs modulus, and lower B/G ratio. These vanadium borides are brittle. We predict that the V5B6 and VB2 are potential superhard materials. The nature of hardness is related not only to covalent bonding but also to bond orientation. The B–B and V–B covalent bonds parallel to the load plane are the origin of high levels of hardness.

Thermodynamic assessments of the Au–Th and As–U systems

The thermodynamic assessments of the Au-Nd and Au-Dy binary systems have been carried out by the Calculation of Phase Diagram (CALPHAD) method based on the available experimental data. The Gibbs free energies of the solution phases including liquid, fcc, bcc, hcp and dhcp were described by the substitutional solution models with the Redlich-Kister equation, and those of the intermetallic compounds were described by the sublattice models. A set of self-consistent and reasonable thermodynamic parameters is obtained for the binary systems, which describes the Gibbs free energies of the solution phases and the intermetallic compounds phases.

Thermodynamic Calculation of Bi-Au-Lu, Nd Ternary Systems

With available melting point and hardness, the Bi-based filler alloy is considered as one choice of high-temperature Pb-free solder. Phase diagram can play an important role in the design of new type of Pb-free solder.In the present work, the thermodynamic assessments of the Au-Nd and the Au-Lu binary systems have been carried out by the Calculation of Phase Diagram (CALPHAD) method based on the available experimental data. The Gibbs free energies of the solution phases were described by subregular solution models with the Redlich-Kister equation, and those of the intermetallic compounds were described by sublattice models. A set of self-consistent and reasonable thermodynamic parameters is obtained for the binary systems, which describes the Gibbs energies of the solution phases and the intermetallic compounds phases. Additionally, combined the reported Bi-Au, Bi-Lu and Bi-Nd binary systems, the thermodynamic database of the Bi-Au-Lu and the Bi-Au-Nd ternary systems have been developed, which will provide important thermodynamic information for the phase equilibria of the multicomponent Bi-based alloy systems.

Influence of Hot Extrusion on Microstructure and Hardness of SiC Particle Reinforced Al-Zn-Mg-Cu Alloy Matrix Composite

In this paper, the microstructure and mechanical property of the Al-Zn-Mg-Cu aluminum matrix composite reinforced by SiC particles with the contents of 2.5, 4.5, and 6.5wt% through vacuum casting are studied. The homogenization treatment was conducted at 465°C heat insulation for 24h. The purpose of this study is to analyze hot extrusion influence on the microstructure and hardness of the Al-Zn-Mg-Cu aluminum matrix composite. SiCp under pre-processing possesses good wetability with the analysis of Laser Particle Sizer and XRD. Metallurgical microscope, XRD, SEM and EDS is applied to analyze the microstructure of the Al-Zn-Mg-Cu aluminum matrix composite. It has proved that the hot extrusion can effectively improve the homogenization of SiCp and dissolve the second rough phases to reinforce the dispersal of CuAl2 and MgZn2 phase. The hardness of Al/SiCp composite rises as the increase of the SiCp content. It is shown that when the SiCp content is above 5%, its hardness obviously reinforced as well as that of the Al/SiCp composite.

Synthesis and Properties of the Poly(styrene-acrylic acid)

Due to the smalle hole of the shale formantion, particles with smaller size, such as nanoparticles was developed to be used as plugging materials during the drilling of shale formation. In this article, poly (styrene-acrylic acid) particles were synthesized by soap-free emulsion polymerization of styrene (St) and acrylic acid (AA). The as-prepared polymer particles were characterized by Fourier transform infrared spectroscope (FT-IR), dynamic light scattering (DLS). In addition, salt tolerance, temperature resistance and compatible properties with additives in drilling fluid of the polymer particles were also investigated.

Effect of Extrusion Texture on Mechanical and Electrochemical Properties of Aluminum Alloy Drill Pipe

Aiming at the special service environment of aluminum alloy drill pipe, in this paper, the influence of extrusion texture on the mechanical and electrochemical properties of aluminum alloy drill pipe was studied. And the macroscopic textures of longitudinal profile and cross section of aluminum alloy drill pipe were tested, and the tensile, compressive and impact mechanical properties were tested, followed by immersion and electrochemical testing. The results show that the texture which 2A12T4 aluminum alloy drill pipe contains is <001> and <111> along the extrusion direction and <223>, <101> in the transverse direction. The test results of mechanical properties show that the extruded texture will affects the mechanical properties of material. When the cross section and longitudinal profile samples of 2A12T4 were soaked in 3.5% NaCl solution at 25°C, 60°C and 90°C, their corrosion resistance are different. The pits of transverse specimens exhibit a dispersed distribution and that of longitudinal specimens are distributed along the extrusion direction.