Distribution Of Main Elements Research Articles

Formation of the Transition Zone "Matrix Alloy - Reinforcing Granules" in the Process of Solid-Liquid Synthesis of Composite Material

Casted composite materials have found certain application in mechanical engineering. Their advantages are lower cost due to the use of casting technology (solid-liquid synthesis), absence of any restriction on the shape and weight of parts. It is known that the transition zone between the matrix alloy and reinforcing phase plays an important role on the level of mechanical properties of cast composites. So, the aim of the study is investigations of transition zone formation during the infiltration of matrix alloy into the frame formed by the reinforcing phase. Copper based alloy was used as a matrix alloy and cast-iron granules were used as a reinforcing phase. Cast composite materials have been exposed for different time during the synthesis. Specimens were studied using electron microscopy. Results on the concentration distribution of main elements (Si, Fe, Cu) in a transition zone are presented. It is shown that the formation of transition zone starts during the infiltration process with further its growth during the exposition at the synthesis temperature. It is established that the formation of the transition zone takes place not only due to elements diffusion but as well due to the dissolution of granules of reinforcing phase. Experiments carried out allow establishing some peculiarities of the transition zone formation. To achieve required level of mechanical properties it is necessary to control the melt temperature and duration of the synthesis of cast composite materials.

The fracture resistance and crack propagation path of L415/N08825 bimetallic composite pipe welded joint

The microstructure, fracture resistance and crack propagation path in the L415/N08825 bimetallic composite pipe welded joint has been carried out using the single-edge notched bend (SENB) specimens. The microstructure in the welded seam is dendritic austenite. There are high-density dislocations in the weld, and ellipsoidal NbC and TiC precipitates are distributed on the dendritic austenite matrix. There is element diffusion between the weld and base metals of the interface, and the concentration distribution of main elements at the interface presents a steep concentration gradient. The J-resistance (J-R) curves of the heat-affected zone (HAZ) and welded seam of the experimental welded joint were obtained, reflecting the HAZ of the L415/N08825 bimetallic composite pipe welded joint has a better fracture resistance than the welded seam. The crack propagation path is approximately straight in all specimens, and both regions extend along grain boundaries. The fracture mode in the HAZ is a ductile fracture. The crack is close to deflect to the interface and is greatly affected by the strength and toughness mismatch of the weld metal (WM) and L415. While, the main crack growth direction and the weld grain orientation have always led to the low fracture resistance of the WM.

Formation of the transition zone “matrix alloy – reinforcing granules” in the process of solid‑liquid synthesis of composite material

The paper is devoted to the formation of transition zone between matrix alloy and reinforcing phase (cast iron granules) during the synthesis of composite casted materials. Results on concentration distribution of main elements (Si, Fe, Cu) are presented. It is shown that the formation of transition zone starts during the infiltration process with further its growth during the exposition at synthesis temperature. As the result dissolution and distraction of granules take place.

Effects of torrefaction and water-washing on the mineral transformation behavior during co-combustion of straw and coal: A CCSEM analysis

Biomass can be torrefied to improve the fuel quality prior to its utilization. In addition, a large number of soluble alkali metals can be removed by water washing, to solve slagging and other ash-related problems. In this study, computer-controlled scanning electron microscopy (CCSEM) was used to analyze the mineral composition and elemental distribution of straw, torrefied straw char, and torrefied-water washed straw char. The mineral transformation behavior and the distribution of main elements, when these biomass species were individually co-combusted with coal, were also studied in detail. The comparison of the mineral composition of bulk ash obtained from torrefied straw combustion and straw combustion revealed that the quartz phase decreased and the aluminosilicates of K-, Na-, and Ca–Fe–K increased in the former compared to that in the latter. After the torrefied straw was washed with water, the quartz and Si-Rich phases increased. K aluminosilicate decreased and the quartz phase increased when the torrefied sample was co-combusted with coal at both mixing ratios of 1:1 and 1:4 compared to straw/coal co-combustion. When the torrefied-water washing sample and coal were co-combusted at a 1:1 ratio, the quartz phase decreased, and the Si-Rich and mullite phases increased. When the straw/torrefied char/torrefied-washed char was co-fired with coal at the 1:4 ratio, the amount of K aluminosilicate was less compared to that observed at the 1:1 ratio. It can be concluded that both torrefaction and torrefaction-washing can reduce the content of low-melting-point aluminosilicates in the mineral composition of the studied biomass after co-combustion, which can be beneficial to alleviate the ash slagging problem.

An in-situ study on the dissolution of intermetallic compounds in the Al–Zn–Mg–Cu alloy

The in-situ SEM observations and Line-scanning methods were used to observe the atomic concentration distribution and evolution of main elements in intermetallic phase at different solid solution temperatures. The results indicated that the atomic distribution of main elements in η (MgZn2), S (Al2CuMg), Fe-containing (Al7Cu2Fe) intermetallic phases are parabolic through these phases, while the non-main elements uniformly distribute in matrix. The results of Differential Scanning Calorimetry (DSC) and Energy Dispersive Spectra (EDS) indicated that the Zn atoms dissolved into the matrix between 245 and 430 °C, under which the process of η phase transits to S phase occurred. The Cu element of S (Al2CuMg) phase has an obviously diffusion rate at 450 °C, while the Mg element has an obviously diffusion rate when the temperature is higher than 460 °C. Afterwards the atomic concentration dissolution was modelled by diffusion law, and the model results is corresponding to the linear rule, which agrees with the experiment results.

Structure and phase composition of material based on vanadium alloy V-4.9Ti-4.8Cr and ferrite steel 17Cr-12Ni-Fe

Three-layer materials consisting of the V-4.9Ti-4.8Cr/ferrite steel 17Cr-12Ni-Fe /V-4.9Ti-4.8Cr were obtained in the paper. Phase composition and microstructure of the transition zone of the three-layer material of vanadium alloy V-4.9Ti-4.8Cr and ferrite steel 17Cr-12Ni-Fe were considered. The use of the method of direct laser growing allowed obtaining a three-layer material with qualitative interconnection of layers, as well as decreasing a multistage nature of deformation and thermal operations used when obtaining a three-layer material in earlier works. Additional thermal treatment of a three-layer alloy led to growth of matrix grains up to 100 μm of the vanadium alloy. A uniform distribution of main elements V, Ti, Cr was observed in the transition zone both before and after annealing. A zone of interdiffusion of the metals amounted to 250-350 μm.

MICRO-CHARACTERIZATION OF DISSIMILAR METAL WELD JOINT FOR CONNECTING PIPE- NOZZLE TO SAFE-END IN GENERATION III NUCLEAR POWER PLANT

The dissimilar metal weld joint(DMWJ) in primary water system of pressurized water reactors(PWRs) has been proven to be a vulnerable component owing to its proneness to different type of flaws. Thus,maintaining integrity of such joint in case of defect presence is of great importance to the design and safe management of nuclear power plants(NPPs). For a reliable integrity analysis of DMWJ, it is essential to understand the microscopic characteristics in all regions of the joint. In this work, OM, TEM, SEM, durometer, AFM, MFM and SKPFM were utilized to investigate the microstructure, micro- hardness and the distribution of main elements, grain boundary characteristic and residual strain in the A508/52M/316 L DMWJ that used for connecting the pipe safeend and the nozzle of reactor pressure vessel in PWRs, and a comparative analysis about the microstructure and property along the radical direction of the DMWJ was obtained. The results showed that there was no region that differed from the other part of the weldment in terms of the microstructure and micro-hardness dramatically. A layer of fine grain resulting from unmelted filler metal was found in the backing weld part of the joint. The residual strain in the heat affected zone(HAZ) of 316 L was higher than that in other regions. Meanwhile, drastic variations in the microstructure, chemical composition distribution and grain boundary character distribution(GBCD) in both the 316L/52 Mw and the 52Mb/A508 interface regions were observed. The analyses using TEM and MFM test showed that a large number of chromium and molybdenum- rich precipitates particles distributed both along the grain boundaries and inside grains in the 316 L base metal, which were identified to be precipitates with complex elementary composition rather than the normal string delta ferrite in 316 L austenitic stainless steel. The SKPFM test result indicated that these precipitates were more prone to be corroded than the base metal. Therefore, further investigation about the cause of deformation and the impacts to the corrosion resistance, particularly the stress corrosion cracking(SCC) sensitivity of the precipitates needs to be carried out.

Microstructural evolution of Al–Zn–Mg–Zr alloy with trace amount of Sc during homogenization treatment

The microstructural evolution of Al–Zn–Mg–Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and differential scanning calorimetry (DSC). The results show that serious dendritic segregation exists in studied alloy ingot. There are many eutectic phases with low melting-point at grain boundary and the distribution of main elements along interdendritic region varies periodically. Elements Zn, Mg and Cu distribute unevenly from grain boundary to the inside of alloy. With increasing the homogenization temperature or prolonging the holding time, the residual phases are dissolved into matrix α(Al) gradually during homogenization treatment, all elements become more homogenized. The overburnt temperature of studied alloy is 476.7 °C. When homogenization temperature increases to 480 °C, some spherical phases and redissolved triangular constituents at grain boundaries can be easily observed. Combined with microstructural evolution and differential scanning calorimeter, the optimum homogenization parameter is at 470 °C for 24 h.

The behavior of noble-metal admixtures during fractional crystallization of As- and Co-containing Cu–Fe–Ni sulfide melts

To study the behavior of macrocomponents and admixtures during the fractional crystallization of sulfide melts and the influence of As on noble metals in this process, we performed a quasi-equilibrium directional crystallization of melt of composition (at.%): Fe—35.5, Ni—4.9, Cu—10.4, and S—48.3, with admixtures of Pt, Pd, Rh, Ru, Ir, Au, Ag, As, and Co (each 0.1 at.%), which imitates the average (by Cu contents) compositions of massive ores at the Noril'sk Cu-Ni deposits. The following sequence of phase formation from melt has been established: mss (zone I) / mss + iss (zone II) / iss (zone III) (mss is (FezNi1–z)S1+δ, iss is (FexCuyNi1–x–y)zS1–z); it corresponds to the distribution of main elements along the sample (primary zoning). Distribution curves for macrocomponents in zones I and II of the sample were constructed, as well as the dependencies of their partition coefficients (k) between solid solutions and sulfide melt on the fraction of crystallized melt. The secondary (mineral) zoning resulted from subsolidus phase transformations has been revealed. Five subzones have been recognized: mss + cp (Ia) / mss + cp + pn (Ib) / mss + pc + pn (IIa) / mss + pc + pn + bn (IIb) / pc + bn + pn + unidentified microphases (III). Admixture species in the sample were studied: (1) admixtures dissolved in primary solid solutions and in main minerals resulted from solid-phase transformations and (2) admixtures forming their own mineral phases. The partition coefficients of Co, Rh, and Ru (mss/L), Ru, Ir, and Rh (mss/cp), and Co, Rh, and Pd (mss/pn) were determined. Minerals of noble metals have been recognized: Pt3Fe, PtFe, Au, (Ag,Pd), (Au,Pt), Ag, Ag3Cu, Au3(Cu,Ag,Pd,Pt), etc., and the regularities of their distribution in the sample have been established. It is shown that some noble-metal admixtures are prone to interact with As. Mineral arsenides and sulfoarsenides of noble metals produced during fractional crystallization have been recognized: PtAs2, Pd3As, (RhAsS), (IrAsS), and (Ir,Rh)AsS. The discovered drop-like inclusions of noble-metal arsenides suggest the separation of the initial sulfide-arsenide melt into two immiscible liquids. By indirect features, the micromineral inclusions are divided into primary, crystallized from melt, and secondary, produced in solid-phase reactions. The results of study are compared with literature experimental data obtained by the isothermal-annealing method and with the behavior of noble metals and As during the formation of zonal massive orebodies at the Noril'sk- and Sudbury-type deposits.

Electrical properties of Cr- and Nb-doped TiO 2 thin films

The series of thin films of solid solutions of TiO 2+ xCr 2 O 3 (0 < x < 0.013) and TiO 2+ yNb 2 O 5 (0 < y < 0.05) were deposited on fused silica by means of reactive RF co-sputtering. The obtained films remain in the amorphous state up to 673 K. Annealing at 1173 K produces a well-developed rutile structure while formation of the anatase structure has not been observed. The high temperature electrical properties such as electrical conductivity, thermopower and work function were investigated within the wide range of oxygen activity (10 -10–10 5 Pa). The effect of both Cr and Nb concentrations and film thickness on the measured parameters was studied. A mechanism for the incorporation of dopants (Cr and Nb) and defect model has been proposed. The influence of both intrinsic and extrinsic defects on the electrical properties has been discussed. The distribution of main elements (Ti, Si, O) as well as impurities were determined by the SIMS method.