Influence Of Flow Velocity On Erosion-Corrosion Performance Of 90º Carbon Steel Elbows In Potash Brine

In this study, the effects of flow velocity and solid concentration on erosion-corrosion behavior of AISI 1018 long-radius steel elbows (Schedule 40) in saturated potash brine were investigated. Potash brine containing 10 and 30 wt% of silica sands flowing at 2.5, 3.0, 3.5 and 4.0 m/s through a continuous loop with pipe internal diameter of 2.54 cm was used as the slurry. All experiments were conducted at 30 ºC. The surface damage on elbows was evaluated using scanning electron microscopy (SEM). It was found that material loss per unit area was greater at high slurry velocity and solid concentration. Corrosion pits were visible on the elbow surfaces at low slurry velocities, but pits were not formed at higher velocities. Mechanical damage was concluded to b

Characterization of aluminum alloy 2618 and its composites containing alumina particles

Metal matrix composites (MMCs) combine a stiff but brittle phase, typically a ceramic, with a more ductile metal matrix. The correct fractional combination of materials can result in a material with improved stiffness, creep resistance, yield stress, and wear resistance relative to the monolithic matrix. The use of MMCs in recent years has become more widespread due to a growing understanding of the dependence of composite properties on a number of factors (e.g., interface properties, metallurgy of the matrix, and stress partitioning between the constituent phases) and appreciation of the problems that can occur in their usage. The purpose of this work was to investigate microstructural evolution in ingot metallurgy AA2618 due to the addition of 10 and 15 vol. % angular alumina (Al2O3) particles. The primary investigative techniques employed were microhardness measurements, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). In addition, other metallographic and data analysis techniques were used. The results of this study showed that the addition of Al2O 3 particles did not alter the aging sequence of AA2618, but it altered certain aspects of the precipitation reaction. It caused the suppression of Guinier-Preston-Bagaryatskii (GPB) zone nucleation, acceleration of the artificial aging response, lowering of peak hardness value, and nonuniform distribution of precipitate and dispersoid phases. However, it did not affect the growth mechanisms for S' and [theta]' formation. The growth parameters obtained for the unreinforced alloy and its composites were not significantly different. Magnesium accumulation around the reinforcing Al2O3 particles was very pronounced. Mg-rich intermetallic particles (suggested to be MgAl2O4 spinel) were observed existing in isolation and embedded in Al2O3 particles. The presence of these particles was considered to be responsible for the low peak hardness obtained for the composites. Also, other intermetallic particles (such as aluminosilicates and Fe-rich particles) were observed. Aluminide (AlxFeNi) particles, which usually occur in AA2618, were determined to possess a variety of chemical formulae. Also, the Al xFeNi phase was determined to be more consistently indexed on the basis a C-centered monoclinic crystal structure with 'a' = 0.867 nm; 'b' = 0.900 nm; 'c' = 0.859 nm; and â = 83.50° rather than the primitive monoclinic structure reported in the literature

An investigation of the corrosion behaviour of a FeNiCoAlTa shape memory alloy in 3.5 wt-% NaCl solution

In this study, the corrosion behaviour of an FeNiCoAlTa (NCAT) shape memory alloy in 3.5% (w w−1) NaCl solution was evaluated. Linear polarisation resistance and potentiodynamic polarisation tests were conducted at 25°C. An open circuit potential (OCP) of −381 mV (vs. saturated calomel reference electrode) and a corrosion rate (CR) of 0.0174 mm y−1 were obtained. The NCAT alloy did not show any passivation in the 3.5% (w w−1) NaCl solution. Its corrosion behaviour was very similar to that of G10180 (AISI 1018) carbon steel with the NCAT showing a lower CR and a less active OCP. Its corrosion in the solution was a combination of general dissolution and localised attack (pitting). Aging heat treatment caused β-Ni3Al phase, and tantalum to precipitate on the grain boundaries, resulting in chemical species segregation between the grain boundaries and the grains. The chemical segregation caused intergranular corrosion of the alloy

Dal cognitivismo all'apprendimento significativo

Polished surfaces of a fine-grained aluminum, silicon carbide metal matrix composite (MMC) were imaged using the ion-induced secondary electron emission in a FIB ion microscope. In these images a dispersion of particles with a distinct bright contrast are seen to be mainly located at the matrix aluminum grain/subgrain boundaries, and at the matrix/reinforcement interface. The particles range in size from 20 to 200 nm. FIB-SIMS was used to identify the composition of these particles as magnesium and oxygen-rich, and so, to corroborate SEM/EDS analyses. Analysis of the FIB images of the polished section showed that the areal density of the particles with distinct bright contrast was consistent with a composition of MgAl2O4