Advanced Materials Research Vols. 146-147

Abstract: Based on the parabolic yield criterion reflected by pressure sensitive and the SD effect, the material constitutive equation is given by orthogonal flow rule. In the plane stress condition, a basic solution in elastic-plastic crack tip field is given. The different structures of solutions with different plastic mixity are analyzed. Different parameters in crack-tip stress field and the singularity in the strain field are discussed. These results provide a theoretical reference for engineering applications.

Abstract: A Cu55Zr40Al5 bulk metallic glass (BMG) was prepared by using copper-mold suction-casting and the structure and thermal stabilities of the amorphous alloy as well as the effect of isothermal annealing on its micro-hardness and friction property were studied. The results showed the glass transition temperature, onset temperature of exothermic reaction, and temperature interval of supercooled liquid region are 746.8 K, 793.5 K and 46.7 K, respectively. The BMG exhibits a micro-hardness value of 483.5 Hv and an average friction coefficient of 0.495. After isothermal annealing treatment, the micro-hardness has been enhanced and presents an upward trend with increasing the annealing temperatures. Meanwhile, the friction coefficients can be significantly decreased and the anti-wear property has been enhanced evidently.

Abstract: The high instability is one of the most important problems for cinnamon oil. The complexation of cinnamon oil by β-cyclodextrin (β-CD) and its controlled release characteristics were investigated in this paper. The composition of microencapsulated cinnamon oil was evaluated using Fourier transform infrared spectroscopy (FT-IR). The size distribution and surface morphology of the resultant microcapsules were also characterized using Beckman Coulter particle size analysis, scanning electron microscopy (SEM), respectively. And the size distribution is narrow and the mean diameter is 20.78 μm. Results demonstrated the rates of cinnamon oil released from microencapsulation were accelerated with the increase of RH.

Abstract: In this paper, a new phenomenological and empirically based constitutive model was proposed to change the temperature term in the original Johnson-Cook constitutive model. The new model can be used to describe or predict the stress-strain relation of the metals deformed over a wide range of temperatures even though the current temperatures are lower than the reference temperature. Based on the impact compression data obtained by split Hopkins pressure bar (SHPB) apparatus about one hot-extrudedMg-10Gd-2Y-0.5Zr alloy, the material constants in the new model can be experimentally determined using isothermal and adiabatic stress-strain curves at different strain rates and temperatures. Good agreement is obtained between the predicted and the experimental flowcurves for the hot-extrudedMg-10Gd-2Y-0.5Zr alloy at both quasi-static and dynamic loadings under a wide range of temperatures ever though the current temperatures are lower than the reference temperature.

Abstract: The influence of grain size on the lattice constant in some nanocrystallites was studied by computing the interactive cohesive energy of the nanocrystallites. The relationships of the lattice constant with the grain size in NaCl, CsCl structure ionic crystallites, FCC, BCC structure metal crystallites and FCC, BCC, SCC structure molecular crystallites was studied respectively. The results are in good agreement with the above experimental ones qualitatively.

Abstract: The aim of the determination is to study formation of precipitations by rapid tempering using thermal simulation tester and effects of precipitations on lower-temperature toughness property. A ultra low carbon microalloyed quenched steel containing alloying elements, such as 0.06wt%C-0.04wt%Nb-0.06wt%V-0.008wt%Ti, is tempered at 620°C for holding time 70min in conventional resistance furnace , and tempered rapidly at 620°C for 40s、80s and 120s, respectively. Both microstructures and impact properties were also investigated. It was observed that the nanoscale cementite particles were obtained by rapid tempering for 40s. Furthemore, the Charpy impcat energy of these specimens holding time 40s is higher than that of others. In comparison with conventionally processed, rapid tempering for low carbon alloyed steel can achieve good toughness due to the nanoscale cementite particles and offer the potential advantage for significant time and cost savings.

Abstract: The incorporation of nano-size TiO2 particles can significantly enhance the microstructure and mechanic properties of Al2O3 coating. Phase transformation from mainly stable α-Al2O3 and anatase-TiO2 in the powders to predominant metastable γ-Al2O3 and rutile-TiO2 in the coatings was observed. Reaction between Al2O3 and TiO2 phase also occurred producing new phase Al2TiO5 phase. Microstructural investigation showed that well separated TiO2 lamellas were homogeneously dispersed between Al2O3 lamellas. It was found that the plasma-sprayed composite coating possessed better wear resistance than that of monolithic Al2O3 coating. The addition of TiO2 was found to improve friction coefficient, wear resistance and fracture toughness.

Abstract: There are situations where baseline fatigue crack propagation (FCP) data are needed but the available material for its evaluation is far from enough to fabricate full sized standard specimens. Miniature specimen testing techniques have been proposed but published data seems to be slightly but consistently slower under the same stress intensity than that from standard specimen results. In this work, an aluminum alloy and a steel, which have vastly different mechanical behaviors, are used to generate different stress states and premature crack closure to allow the validity of miniature specimen FCP data to be critically examined.

Abstract: This paper presents a downhole increase in the pumping process used in the rack device processing technology and processing methods. Discussed the process in the processing rack process assurance measures and control of machining accuracy rack approach.

Abstract: The electrochemical behavior of copper in various concentrations of NaHSO3 solution was investigated with linear polarization and cyclic voltametry technique at room temperature. The results showed that the concentration of bisulfite ions has noticeable effects on the behavior of copper. With HSO3 -concentration increasing, the passivity region, ascribed to the formation of absorption layer Cu (HSO3) ads - or Cu (SO4) ads 2-, appearing at the lower potential range in the polarization curve inclined to transform into an active region; whereas another passivity region, due to the appearance of CuO or Cu2O layer on the surface, took place at a higher potential region. The formation and the reduction of CuO or Cu2O were irreversible.