Effect of solute atom adsorption on heterogeneous nucleation by in-situ MgO particles:Experimental and theoretical studies

The introduction of oxide inclusions during the smelting process has a clear promising heterogeneous nucleation potency on Mg-based alloys, but the mechanism has not been explored clearly yet. In the present work, the grain refinement mechanism of MgO in pure Mg,Mg-3Al and AZ31(Mg-2.9Al-0.9Zn-0.3Mn) alloys is investigated by combing first-principles calculations and experiments. The theoretical results show that solute atoms adsorption will affect the nucleation and the subsequent growth process, which is an important factor affecting the refinement efficiency. A contradiction between the experimental results and the grain growth restriction factor(GRF) theory is observed,that is the refinement ratio of AZ31 is worse than Mg-3Al alloy. This is explained by an adsorption model which reveals that Al promotes the adsorption of Mg on MgO surface so as to stimulate more particles available as nucleating sites. Meanwhile, Fe and Mn also have favorable effects on the adsorption of Mg, Zn may play the opposite role compared to Al. The theoretical analyzes provide a strong support to the experiments that Al benefits the initial nucleation of α-Mg on MgO to promote the grain refining effect of Mg-3Al prior to AZ31 alloy.

Grain refinement of Mg-Al alloys inoculated by MgAl_(2)O_(4)powder

As a potent nucleating substrate forα-Mg grain,MgAl_(2)O_(4) powder was used to inoculate the Mg-Al melt in this study.The effects of MgAl_(2)O_(4)amount,holding time and Al content on the grain size and grain refining ratio of the inoculated Mg-Al alloys are systematically investigated.The results show that the minimum grain size of Mg-3Al alloy is achieved by adding 2wt.%MgAl_(2)O_(4)powder and this alloy exhibits higher grain refining ratio than Mg-5Al and Mg-8Al alloys.The crystallographic misfit calculation indicates the wellmatching and possible orientation relationships(ORs)betweenα-Mg and MgAl_(2)O_(4).Among these predicted ORs,[10–10]α−Mg//[110]MgAl2O4 in(0002)α−Mg//(1–13)MgAl2O4 possesses the smallest misfit,i.e.,2.34%(fr).Both results of the experiment and crystallographic calculation demonstrate that the grain refinement of Mg-Al alloys is attributed to the MgAl_(2)O_(4)particles acting as the heterogeneous nucleation substrates forα-Mg grains.

Effects of Strip Casting and Annealing on Electrochemical Properties of LPCNi_(3.55)Co_(0.75)Mn_(0.4)Al_(0.3) Hydrogen Storage Alloys

The effect of thickness (1 similar to 10 mm) of the ingots on the electrochemical properties of as-cast and annealed strip cast LPCNi3.55Co0.75Mn0.4Al0.3 hydrogen storage alloys was investigated. It is found that the 0.2 C discharge capacity of as-cast LPCNi3.55Co0.75Mn0.4Al0.3 alloy increases with the increase of the thickness of the ingots. As-east alloy with the thickness of 10 mm shows better activation property, higher 1C discharge capacity and better cyclic stability than others. It is mainly contributed to its larger unit cell volume and less internal stress. Annealed LPCNi3.55Co0.75Mn0.4Al0.3 alloy with the thickness of 3 mm shows much better comprehensive electrochemical properties than as-east one; The cyclic. stability of the alloy with the thickness of 6 mm and the activation properties of the alloys with the thickness of 3 similar to 6 mm are improved after annealing. It is mainly owing to the great release of internal stress and the decrease of the segregation of Mn in the alloys.

Synergistic refining mechanism of Mg-3%Al alloy refining by carbon inoculation combining with Ca addition

Mg-3%Al alloy was refined by carbon inoculation combining with 0.2%Ca addition.High grain refining efficiency was obtained and the synergistic refining mechanism was deeply discussed in the present study.Al-C-O particles,actually Al4C3 particles,were formed in the carbon-inoculated Mg-3%A1 alloy acting as nuclei forα-Mg grains.Ca addition had no obvious effect on size distribution of the nucleating particles.Ca segregation was proved on Al4C3 particles,which should reduce the interfacial energy of nuclei/Mg.The constitutional undercooling in front of nucleus/liquid was increased from 0.12℃to 0.15℃induced by 0.2%Ca addition.The synergistic grain refining efficiency can be attributed to the higher constitutional undercooling and lower the interface energy of nucleus/Mg induced by Ca addition.More nucleating particles with small size could be activated acting as potent nuclei ofα-Mg grains.Consequently,Mg-3%Al alloy could be effectively refined due to the synergistic effect induced by carbon inoculation combining with Ca.

Influence of annealing temperature on electrochemical properties of rapidly quenched LPC(NiAlMn)_(4.25)Co_(0.75) hydrogen storage alloy electrodes

The influence of annealing temperature on the electrochemical properties and structure of the rapidly quenched LPC（NiAlMn）4.25Co0.75 hydrogen storage alloys was investigated, in which LPC represents the abbreviation of Nd-free La-Ce-Pr mischmetal after the extraction of most of Ce and Nd. After the annealing treatment between 700900 ℃ for rapidly quenched alloys, their discharge capacity becomes larger and the P-C-T plateau tends to be flatter and lower. The alloy annealed at 700 ℃ has the highest discharge capacity and flattest plateau. The analyses by X-ray diffraction （XRD）, different thermal analysis（DTA）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） indicate that the microstructure reversion and recrystallization occur during the heating, and their feature temperatures are 477 ℃ and 696 ℃ respectively. The annealing treatments make cell volume increase, dislocations and strain decrease, and the distribution of alloy composition become homogeneous.

Prediction Model of Antibacterial Activities for Inorganic Antibacterial Agents Based on Artificial Neural Networks

Quantitatively evaluation of antibacterial activities of inorganic antibacterial agents is an urgent problem to be solved. Using experimental data by an orthogonal design, a prediction model of the relation between conditions of preparing inorganic antibacterial agents and their antibacterial activities has been developed. This is accomplished by introducing BP artificial neural networks in the study of inorganic antibacterial agents. It provides a theoretical support for the development and research on inorganic antibacterial agents. Key words inorganic antibacterial agent - antibacterial activity - neural networks - nanometer material

Spectral Properties of Ce-Loaded TiO_2

Using nano-anatase TiO_2 powder and Ce(NO_3)_3 as raw materials Ce-loaded nano-TiO_2 was prepared by impregnating method, and characterized by XRD, TEM and UV-Vis spectrophotometer. The UV-Vis reflective spectra of nano-TiO_2 and Ce-loaded nano-TiO_2 were compared. The result shows that Ce-loaded nano-TiO_2 is still of anatase structure with Ce distributing uniformly on nano-TiO_2 surface. A red shift is observed in the UV-Vis adsorption spectrum with its mechanism being discussed.

Investigation on the 773 K isothermal section of La-Fe-Sn ternary systems by X-ray powder diffraction

The 773 K isothermal section of the La-Fe-Sn ternary system was investigated and constructed by X-ray powder diffraction（XRD）.The existence of two reported ternary intermetallic compounds,La6Fe13Sn and La3FeSn6,is confirmed in this work.Compared with other R-Fe-Sn phase diagrams（R = Pr and Sm）,the binary alloys Fe3Sn and Fe5Sn3 are not present.The compound Fe3Sn2 was observed from the XRD pattern of Fe3Sn2 samples,but it is not an equilibrium phase at 773 K and decomposes into Fe and FeSn phases completely for a longer heat treated time.Up to now,the crystal structure data of La2Sn3 has not been reported,so the X-ray pattern of La2Sn3 was only estimated.The phase relationship for this compound was drawn by a dotted line.

Effects of hydrogen on fatigue life of Ti-4Al-2V titanium alloy

Four hydrogen contents were employed to investigate the effects of hydrogen on fatigue life of Ti 4Al 2V titanium alloy by means of section varied samples. Results reveal that the fatigue life of the materials with (116～280)×10 -6 hydrogen is higher than that of natural hydrogen material provided that the fatigue load Δ σ is over 550 MPa. At higher Δ σ , the content of hydrogen has small effects on fatigue life within (116280)×10 -6 hydrogen. For material containing 280×10 -6 hydrogen, fatigue cracks tend to initiate at sample edges at higher load, in contrast, to initiate at sites of hydrides at lower load. The interstitial hydrogen atoms softening the persistent slip bands(PSB) and hydrides separating from the body become the cause of decrease in fatigue life. Hydrides resolved into the body is observed at lower Δ σ for material with 280×10 -6 hydrogen, which is the result of concentration of hydrogen atoms at crack tips and stress induced re precipitation of hydrides.

Coupled Thermo-Mechanical Modeling of Long Cone-Shaped Forging Based on Rigid Visco-Plastic FEM

Based on synthetically considering the coupled thermo mechanical relations between temperature and deforming, a numerical simulation of the forging process for the special long cone shaped workpiece of Al 5.44Mg 2.15Li 0.12Zr alloy at high temperature was conducted by using the rigid visco plastic finite element method. The relations between the total load and the displacement during the forging, and the distributions of stress, strain, temperature and strain rate, which can provide useful information for the process design, are obtained.

Identifying Optimal Cutting Parameters in Drilling of Titanium Aluminum Vanadium Using Finite Element Analysis

Titanium alloys are widely used in the aerospace industries because of their excellent strength-to-weight ratio, high resistance to corrosion, high chemical reactivity and low thermal conductivity and ability to withstand high temperatures. However, these properties make titanium alloys difficult to machine. Drilling of titanium alloy may generate high temperature and high cutting forces. This paper is aimed at determining the suitable cutting parameters in the drilling of titanium alloys to minimize the cutting temperature and cutting forces. A finite element 3D model of the drilling process is simulated in this research. A combination of drilling speeds and feed rates are simulated to obtain the resulting responses of cutting force and temperature. The central composite design (CCD) is used to generate different combinations of cutting parameters to reduce the number of experiments and optimize the temperature and cutting force responses. Results show at the drilling speed of 5000 rpm with a feed rate of 0.1 mm/rev, temperature and cutting force significantly reduced.

Researches on Mischmetal Preventing Lead Segregation in High Lead Bronze

The effect of mischmetal addition on lead segregation in high lead bronze(grade ZQPb25-5)is studied in this paper.The testing results confirm that 0.5 to 1.0% misehmetal addition can effectively prevent lead from gravity and inverse segregation.The results of preventing lead from segregation respectively by mischmetal and nickel are also compared in the paper.The mischmetal addition in high lead bronze is distributed in the copper matrix mainly in the form of a compound which promotes early precipitation and refinement of α-dendrites, thus restraining the Pb-rich melt from either sinking to the bottom or escaping to the surface layer of the casting.As a result,the tendency of lead segregation is significantly decreased.Proper addition of mischmetal can also improve the mechanical properties,especially the ductility of high lead bronze.In addition,the contents of tin in high lead bronze can partially be substituted by mischmetal addition.

THE FORMULA OF MEASURING m VALUE IN SUPERPLASTIC BULGING BY MEANS OF JUMP PRESSURE

Ⅰ. INTRODUCTIONThe index m value of strain rate sensitivity is an important mechanical factor for evaluating superplasticity. The authors have established the analytically mechanical theories of m value on the basis of many formulae for measuring rn value by means of tension and have given out a unified measuring methodt. m value is affected by stress status because

SILICON EFFECTS ON THE NODULIZING OF CARBIDES IN AS-CAST MEDIUM MANGANESE STEELS

Water toughening is generally required for the widely used manganese-system wear-resistant cast steels (0.9-1.4 % C, 5.5-14.0% Mn). The purpose of the treatment is to get rid of the needle-like carbides and carbide networks in the as-cast state,