The Effect of NiAl Coatings on Oxidation Behavior of AISI 403 Stainless Steel

STAINLESS STEEL TYPE AISI403possess a highdegree of resistance to atmospheric corrosion becauseof its ability to form a dense adherent oxide film,whichprotects the material from further attack[1].Thiscomposition was developed to meet the requirementsfor some gas turbine components.The alloy is notparticularly recommended for use in hot corrosion andoxidation environments.Therefore,a protective coatinglayer is essential for such applications as hot sectioncomponents in gas turbine[2].A…     

Formation and Microstructural Characterization of Silicon-modified Aluminide Coating on Nickel-based Superalloy IN738LC

ALUMINIDE COATINGS are used extensively forprotecting gas turbine hot section components due totheir high oxidation resistance and low capital cost.However,for some application,their properties must bemodified by adding elements such as Cr,Si and Pt tomeet high performance gas turbines requirements[l,2].Although silicon is less efficient as a protective scaleformer than chromium and aluminum,silicon-modifiedaluminide coatings,have shown better hot corrosionresistance(specially to type …     

Effects of ARB and ageing processes on mechanical properties and microstructure of 6061 aluminum alloy

Accumulative roll bonding (ARB) has been used as a severe plastic deformation process for the production of high-strength materials. Ageing treatment has been found to enhance the strength of alloys by precipitation of a second phase. In the present work, ARB followed by the ageing process was used for the fabrication of the high-strength 6061 aluminum alloy. Samples of the alloy thus made were subjected under annealed and ARBed conditions to ageing treatment at different temperatures for different times and their mechanical properties were evaluated. It was found that the microhardness and tensile strength of the specimens increased with the number of ARB cycles but their elongation values decreased. After the ageing treatment, the mechanical properties of the ARBed specimens improved in terms of both strength and ductility. Based on TEM observations, it may be concluded that the improved mechanical properties after the duplex ARB-ageing process can be attributed to the precipitation of very fine particles with a slight decrease in dislocation density and limited structure coarsening. SEM observation of fracture surfaces of aged specimens indicated that the fracture was predominantly caused by microvoid coalescence at constituent particles.     

Investigating microstructural evolution during homogenization of the equiatomic NiTi shape memory alloy produced by vacuum arc remelting

The vacuum arc remelting process is widely used for the commercial production of NiTi shape memory alloys. Due to the absence of electromagnetic forces in this method, several remelting and long-time homogenizing are required. In this work, a Ti-50 at.% Ni alloy was prepared using the non-consumable vacuum arc melting technique in a water-cooled copper crucible. After four times of remelting process, specimens were subjected to homogenization at 1000 °C. Micro/macrostructural changes during homogenization were investigated by optical microscope and SEM equipped with EDS analyzer. The results showed that the as-cast specimen consisted of mostly Ni₃Ti, Ti₂Ni and monoclinic (B1^9′) phases with high segregation. By increasing the holding time during the homogenization process at 1000 °C, the amount of austenite (B₂) phase was increased, while segregation and unfavorable phases, and accordingly, hardness were decreased. After 4 h of homogenization, austenite (B₂) was the only phase maintained in the microstructure of Ti-50 at.% Ni. In addition, macrostructure of the alloy was turned into polygonal structure after such a homogenization treatment.     

A comparative study of corrosion performance of sealed anodized layers of conventionally colored and interference-colored aluminium

The nanostructure of aluminium anodized layer was modified in phosphoric acid to induce light-interference colors through electrocoloring using nickel pigments. After a mixed sealing procedure, the corrosion performance of the interference-colored anodized layer was evaluated using Tafel polarization and electrochemical impedance spectroscopy. The results were compared with those obtained for conventionally colored anodized layer. The modification made the mixed sealing of subsequent colored layer less effective. The steam-sealing was found to be more effective for sealing the interference-colored anodized layer. For effectively sealed layers, the porous layer plays an additional role besides the barrier layer in determining the corrosion performance.     

Effect of Catalyst on the Formation of Silica Coating on Nickel Substrate by Sol -Gel Processing

The sol-gel process lends itself very successfully tothe production of thin glass films either by a dipcoating or a spin coating procedure[1,6].Recentdevelopments in this area include the production ofcoatings such as ferrites coatings[13],piezoelectriccoatings[11],superconductor coatings[11],dielectriccoatings[10,11],protective coatings[17],anti-reflection coatings[11,12],biomedical coatings[17]and coatings for optical sensor application[3].Sol-gel-derived nano-porous silica films have manyun…     

Effect of Water Content of Synthetic Hydrogel on Dehydration Performance of Nanoporous LTA Zeolite Membranes

Nanoporous LTA‐type zeolite membranes were synthesized on α‐Al₂O₃ disk as substrate using secondary growth method. A gel formula of 1 Al₂O₃: 2 SiO₂: 3.4 Na₂O: W H₂O in molar basis was chosen while its water content (W) was varied. Four levels of water contents of 140, 155, 175, and 200 were selected for membrane synthesis. The results showed that the best membrane was synthesized with water content of 155. The most efficient zeolite membrane showed a permeation flux of 0.5 kg/m²/h and a separation factor of 3800 in dehydration of a 5/95 (wt%) water/isopropanol mixture at 298 K.     

Mass Transfer Simulation of Gold Extraction in Membrane Extractors

The extraction of gold in membrane extractors was theoretically investigated. Extraction of gold in the form of $ {\rm Au(CN)}_2^- $ in a solution of n‐heptane and synergistic extractants of LIX79+TOPO was studied. The membrane extractor consists of three sections: the tube side, the membrane, and the shell side. Conservation equations were derived for $ {\rm Au(CN)}_2^- $ in the membrane module and were numerically solved based on finite element method. Simulations were conducted through solving the momentum and mass transfer equations simultaneously. It was indicated that as the feed flows within the tube side, it moves into the membrane due to the concentration difference, and then gets swept by the moving extractants within the shell side. The distribution of solute concentration in the membrane contactor was obtained. Simulation results showed increasing the feed flow rate reduces the extraction efficiency, while doing the same for the organic phase flow rate does not change the extraction efficiency.