Effect of Zr on behavior of compressive creep in as cast ZA27 alloy

The effect of Zr on the behavior of compressive creep in as cast ZA27 alloy was investigated in the temperature range of 20160 ℃ and under different compressive stresses in the range of 50137.5 MPa with special apparatus. The results show that the primary compressive creep strains and steady creep rates of ZA27 Zr alloy and ZA27 alloy increase with increasing temperature and stress. However, the primary compressive creep strain and steady creep rate of the ZA27 Zr alloy are lower than that of the ZA27 alloy below 100 ℃, but higher at 160 ℃. The compressive creep behaviors in both ZA27 Zr alloy and ZA27 alloy obey an empirical equation ln t=C-n ln σ+ Q/RT , and the exponent stress n is 3.63 for ZA27 Zr alloy and 3.46 for ZA27 alloy, respectively, the activation energy Q is 87.32 kJ/mol for ZA27 Zr alloy and 81.09 kJ/mol for ZA27 alloy. Different material structural constants are associated with different compressive creep behaviors in the alloy. The compressive creep rate in the alloy is controlled by the lattice diffusion of zinc and dislocation limb.

Evaluating Acceleration Ability of Electrons of SiO_2 and ZnS in ZnS∶Er Electroluminescence

In layered optimization scheme and solid state cathodoluminescence, silicon oxide plays a very important role in obtaining high energy hot electrons to excite luminescent centers or organic luminescent ma terials. The acceleration ability of electrons of SiO2 and ZnS was compared through the variation of emission intensity based on ZnS：Er phosphor during the reverse of polarity of sinusoidal voltage. The ratio of maximum emission intensity under positive and negative half period is 2.18. This result not only demonstrates that parts of primary electron comes from electrode, but electrons in conduction band of SiO2 can be heated to higher energy than that of ZnS.

Evolution of Sm2Fel7 Alloys during Hydrogenation-Disproportion Process

The evolution of phase compositions, phase change and microstructure in Sm2Fe17 alloys during hydrogenationdisproportion process were systematically studied with XRD, SEM, EDX methods. Research indicates that HD process of Sm2Fe17 alloys is as follows： Sm2Fe17 alloy absorbs hydrogen first in the atmosphere of hydrogenation with a pressure of 0.1 MPa. Disproportionation begins at T ≥ 500 ℃, then the alloys tuna into lots of SmHx and α-Fe phases which are partly in microcrystal or amorphous structures. Along with the increase of temperature, the microcrystal and amorphous structures transformed into crystal structure and this transformation thoroughly completed at 750 ℃. The size of obtained crystal grain is about 20 - 100 nm. Based on the experimental data, a microstructural transformation model of Sm2Fe17 alloys during hydrogenation-disproportion process was made.

THE ROLE OF RARE EARTH CHLORIDES IN THE PACK-TiC COATING AGENT

If 1% rare earth chloride is added to the coating agent containing 5% AlCl_3,the coating efficiency of TiC will be increased greatly.A protective crust consisting of Al_2(SiO_3)_3 and SiO_2 will form on top of the coating agent in the temperature range of 850～1000℃ when SiO_2 powder of a thickness of 5～10 mm is spread on top of it.The protective crust can offer a good air-proof property and increase the denseness of the coating structure.

Negative creep during compressive creep of as-cast ZA27 alloy

The negative creep during compressive creep deformation of as cast ZA27 alloy was investigated at the temperature range of 20160 ℃ and at compressive stress levels from 50137.5 MPa with special apparatus. Results show that the negative creep in the alloy occurred respectively at 20 ℃ (50 MPa, 87.5 MPa and 100 MPa), 60 ℃(50 MPa and 87.5 MPa) and 100 ℃(50 MPa). According to the phase transformation and theoretical analysis, the negative creep resulted from volume expansion caused by four phase transformation α+ε→T′+η in the alloy. The theoretical analysis is consistent with the experiment results. And the values of negative creep depended on the difference between the compressive creep deformation and the volume expansion.

Evaluation of Students'Performance in Specialized Courses in Yanbian Agriculture College by Variance

The performance of college students'professional courses is an index to evaluate their academic status,so the performance of professional courses has a certain significance.In the process of assigning homework to teachers and taking exams in universities,the performance of specialized courses is regarded as the standard for students to study well.Because students'understanding and follow-up are often assessed on the basis of their usual seriousness and attendance in class,homework and exams,it is necessary to analyze their final grades to assess their actual situation.Test scores were evaluated using variances and covariances.This paper discusses how to evaluate the final achievement from the distribution of achievement.

Zn-doped nickel iron(oxy)hydroxide nanocubes passivated by polyanions with high catalytic activity and corrosion resistance for seawater oxidation

Electrochemical water splitting to produce hydrogen fuel is a promising renewable energy-conversion technique.Large-scale electrolysis of freshwater may deplete water resources and cause water scarcity worldwide.Thus,seawater electrolysis is a potential solution to the future energy and water crisis.In seawater electrolysis,it is critical to develop cost-effective electrocatalysts to split seawater without chloride corrosion.Herein,we present zinc-doped nickel iron(oxy)hydroxide nanocubes passivated by negatively charged polyanions(NFZ-PBA-S)that exhibits outstanding catalytic activity,stability,and selectivity for seawater oxidation.Zn dopants and polyanion-rich passivated surface layers in NFZ-PBA-S could effectively repel chlorine ions and enhance corrosion resistance,enabling its excellent catalytic activity and stability for seawater oxidation.

DEFORMATION LOCALIZATION AND SHEAR BAND FRACTURE IN STRONG ANISOTROPY SHEET TENSION

The tensile deformation localization and the shear band fracture behaviors of sheet metals with strong anisotropy are numerically simulated by using Updating Lagrange finite element method, Quasi-how plastic constitutive theory([1]) and B-L planar anisotropy yield criterion([2]). Simulated results are compared with experimental ones. Very good consistence is obtained between numerical and experimental results. The relationship between the anisotropy coefficient R and the shear band angle theta is found.

Crystallographic mechanism of inverse twinning in ordered β′-CuZn alloy

The basic process of mechanical twinning in β’-CuZn phase, as an example of B2 structured metals, has been analyzed under the rolling stresses. The behavior of inverse twinning in B2 structured metals is discussed in terms of mechanics and crystallographic stability. It is shown that the inverse twinning could remain the B2 structure, and the resulting strains will have the lowest resistance during the rolling deformation of the polycrystalline.

Thermal residual strain in silicon carbide whisker reinforced aluminium-matrix composite

When metal matrix composites are cooled down to room temperature from the fabrication or quench temperature, residual stresses are introduced in them. The residual stresses will affect deformation, fracture and dimensional stability of the composites.