Al2O3 and ZrO2 ceramics thin coating test was performed on the surface of high strength Ni based super alloy by ion plating technique to prevent fission product (FP) plate-out contamination from helium gas turbine, and these ceramics coated specimens were tested to examine its contamination protection behavior and cyclic heat shock resistance. The following conclusions were derived; (1) Less than 4 μm thickness of Al2O3 and ZrO2 ceramic coating layer were formed on the surface of super alloy by ion plating technique and highly densified and homogeneous Al2O3 ceramic coating layer were obtained with surface roughness under ±10 nm. (2) There was no breakaway and dropout in Al2O3 coating layers under 100 cyclic heat shock test between 1173-288 K. However, crack in Al2O3 ceramic coating layer was found over 100 cycles. (3) It was found that there was no plate-out of vaporized Ag onto the Al2O3 ceramic coated specimen on the same heat transfer fluid conditions of gas turbine system, whereas Ag plate-out was found in the cracked Al2O3 and ZrO2 coated specimens damaged by long cyclic heat shock test.
Nd2Fe14B molten alloy droplets were containerlessly solidified using a 25 m drop tube. The relationship between the sample diameter and the microstructure was investigated. The diameter of the resultant spherical samples was in the range from 150 to 2000 μm. When sample diameter was larger than 500 μm, the microstructure of the spherical sample consisted of the α-Fe phase embedded in the Nd2Fe14B matrix within entire sections. In the spherical sample with diameter of 400 μm, the microstructures consisted of two regions, one was Nd2Fe14B columnar grains and the other was α-Fe phase embedded in Nd2Fe14B matrix. The columnar Nd2Fe14B region expanded as the sample diameter decreased from 400 μm to 350 μm. When sample diameter reduced to 250 μm, the microstructure of the spherical samples consisted of the pure Nd2Fe14B dendrite without any α-Fe phase.
Titanium carbide (TiC) reinforced aluminum composites were fabricated by combining a combustion reaction and a vortex technique. First, the base composite, consisting of Al and fine TiC particles, was synthesized by combustion of a compacted Ti-C-Al powder blend. The TiC particles synthesized in situ were spherical, with diameters of 2-5 μm. Then the base composites were put in molten Al and stirred. The TiC particles in the base composite were easily incorporated and dispersed uniformly in the Al matrix by very brief stirring. In contrast, when commercial TiC powders were used, they were poorly incorporated and distributed by the same brief stirring. The 0.2% proof stress and ultimate tensile strength of the composites were significantly improved compared with the aluminum matrix, and increased with increasing TiC content. The mechanical properties of the aluminum composites fabricated using the base composite were roughly equal to those using commercial TiC powder.
Characterization at the ceramic top-coat/metallic bond-coat interfacial region was conducted for several kinds of the plasma sprayed thermal barrier coating (TBC) systems by means of a transmission electron microscope (TEM), an electron probe micro-analysis (EPMA) and so forth, in order to find out the optimum compositional and structural conditions of the coating components together with the optimum coating processing condition for designing the advanced TBC systems. Specimens with different coating features were prepared systematically by using different coating parameters such as the top-coat spraying conditions and reheat-treatment conditions. Especially, the reheat-treatment was applied to the TBC specimen with different temperature either in air or in inert argon (Ar) gas atmosphere. It was found that in the case of reheat-treatment in air the thermally grown oxide (TGO) was developed at the interface as multiple oxide layers; one is Al2O3 layer developed discontinuously at directly above the bond-coat and another is the mixed oxides layer consisting of the Al, Cr, Co, Ni oxide particles on the Al2O3 layer. Such a TGO layer was heterogeneous and imperfect layer with containing many kinds of defects. On the contrary, the TGO layer formed by the reheat-treatment in Ar was composed dominantly of the continuous and fairly purified Al2O3 layer with large grain size and homogeneous layer thickness. The growth mechanism and influencing factors for TGO were discussed in some detail on the basis of the nano-characterization and quantitative evaluation of TGO.
The rate of As elimination from molten copper by the use of Na2CO3 slag was measured at 1523 K. The results obtained under the present experimental conditions show that As in molten copper is eliminated in a penta-valent form and that its elimination rate increases with increasing initial oxygen concentration in molten copper. Based on the results obtained in the present study, the overall rate of As elimination is considered to be controlled by mass transfer in molten copper. The mass-transfer coefficient of As in molten copper at 1523 K was determined to be 1.3 (±0.4)×10-4 m · s-1 based on the mass balances of As and oxygen in the molten copper and slag phases and the equilibrium relation of the As elimination reaction at the slag-metal interface. In addition, the behavior of the simultaneous elimination of As and Sb which coexist as impurities in molten copper at 1523 K were also investigated from the kinetic viewpoints. The results obtained show that the elimination rate of As is much faster than that of Sb, and two types of elimination behaviors are observed, depending on the initial oxygen concentration in molten copper, i.e. at relatively low initial oxygen concentration, As being preferentially eliminated with stagnation of the Sb elimination, while both elements being simultaneously eliminated at relatively high initial oxygen concentration. These behaviors were examined from the viewpoint of the oxygen concentration at the slag-metal interface during the process.
Solubilities of Al3Ti at 1273-1623 K and TiB2 at 1373-1573 K in molten Al were measured, and the excess partial molar Gibbs energies of titanium and boron in molten Al of liquid standard state at infinite dilution were determined as follows. GeTxi*(l) = RT ln γ°Ti(l) = 95800(±790)+24.5(±0.70)T (J/mol) [943∼1623 K] GeBx*(l) = RT ln γ°B(l) = 18600(±1100) (J/mol) [1373∼1573 K] Also, solubility of AlB12 at 1273-1573 K in molten aluminum was measured, and the standard formation energy of AlB12 was evaluated as a following equation with the determined thermodynamic property of boron in molten aluminum. Al(l) + 12B(s) = AlB12(s) ΔG°fAlB12 = −379000(±23000) + 177(±15)T (J/mol) [1273∼1573 K]
We have investigated the electrical resistivity, magnetization and magnetoresistance for the Heusler-type (Fe1-xRux)2VAl alloys. While Fe2VAl (x=0) exhibits a semiconductor-like behavior with the resistivity reaching 30 μΩm at 2 K, a slight substitution of Ru for Fe causes a sharp decrease in the resistivity and the magnetization at low temperatures. This is taken as an evidence that the moment of magnetic defects decreases upon Ru substitution. Also the large magnetoresistance effect observed for Fe2VAl (x=0) decreased with increasing Ru concentration x. We believe the large magnetoresistance for x=0 to arise from spin fluctuations of magnetic defects caused by occupancies of Fe atoms on the nominally V sites in Fe2VAl. It is also found that a linear relation holds between the electrical resistivity ρ, say at 2 K, and the corresponding magnetoresistance Δρ/ρ in (Fe1-xRux)2VAl alloys.
Bare and anodically oxidized Ni(110) surfaces in 0.05 kmol m-3 Na2SO4 (pH=6.5) and 0.01 kmol m-3 NaOH (pH=12) aqueous solution have been investigated by in-situ electrochemical atomic force microscopy (EC-AFM) with atomic resolution. We have succeeded in in-situ observation of unreconstructed Ni(110)-(1×1) structures in both 0.05 kmol m-3 Na2SO4 and 0.01 kmol m-3 NaOH solution. Under passive region, we have observed well-ordered structures differing from those of the bare surfaces and we found that surface structure of anodically oxidized Ni(110) in 0.05 kmol m-3 Na2SO4 solution agrees with NiO(110), whereas that in 0.01 kmol m-3 NaOH solution agrees with β-Ni(OH)2(0001). These EC-AFM observations reveal the following orientation relationship of the surface structures on the anodic oxide layers and the substrates: NiO(110)//Ni(110) and NiO(110)//Ni(110) in neutral solution, and β-Ni(OH)2(0001)//Ni(110) and β-Ni(OH)2(0001)//Ni(110) in alkaline solution.
Bi2Te3 thin films were electrochemically deposited from ammonia-alkaline solution containing Bi(NO3)3, TeO2, nitrilotriacetic acid (NTA), in which Bi(III)- and Te(IV)-species were dissolving to form Bi(NTA)23- complex and TeO32-, respectively. This study revealed the relationship between [Bi]/[Te] ratio in the solution and the respective metal ratio in the deposited film. The [Bi]/[Te] ratio of the deposited film was successfully controlled by conducting electrodeposition under diffusion-limited conditions, i.e. the [Bi]/[Te] ratio in the solution was linearly related to that of the deposited film, where the partial current density originating from bismuth and tellurium ion was directly proportional to the concentration of respective ions. Dense and crystalline Bi2Te3 thin films with stoichiometric composition were electrodeposited at the potential ranging from −0.6 to −0.8 V from 5.0×10-3 kmol m-3 Bi(NO3)3 · 5H2O, 3.0×10-3 kmol m-3 TeO2 and 0.1 kmol m-3 NTA solution, with cathodic current efficiencies being above 85%.
Samples of Mg-3%Al-1%Zn(AZ31) alloy containing 0∼0.5 mass%Mn were prepared. They were then hot rolled and subsequently annealed. The effect of the amount of Mn content on their microstructures and deformation behavior during tensile tests was investigated. As Mn content increases, a large amount of Al-Mn compounds is crystallized in the alloys. The grain sizes of hot rolled specimens are significantly reduced but there is only a slight difference in the grain size of each alloy. After annealing for 1 h, significant grain growth occurs in 0%Mn alloy. On the other hand, the grain growth is sufficiently suppressed at 0.15%Mn content but it is hardly affected by further Mn addition. The tensile strength and 0.2% proof stress are improved by Mn addition of 0.05% or more, but those of the 0.1%∼0.5%Mn alloys are almost the same, because particles of Al-Mn compounds do not contribute to the strength of the alloys. In the annealed specimens, larger elongations are obtained in 0.15%Mn-containing alloy than in other alloys due to activation of non-basal slip and uniform elongation without deformation band.