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[en] Our oil explorations both onshore and offshore have thrown open bright prospects of cogeneration by using natural gas in gas turbine power plants with heat recovery units. Both for co-gen and combined cycle systems, supplementary firing of GT exhaust gas is normally required. Hence, duct burners have significant role for effective contribution towards of efficacy of heat recovery system for gas turbine exhaust gas. This article details on various aspects of duct burners in heat recovery systems. (author)
[en] In the present study, laser bending of AISI 304 stainless steel sheet has been attempted with a high power (2 kW) continuous wave CO2 laser. Bending angle was measured as a function of laser/processing parameters including power density, scan speed, number of passes and sheet thickness. Following laser bending, microstructural evolution (using a scanning electron microscope) and phase analysis (by X-ray diffraction technique) were systematically carried out to study the effect of laser irradiation and thermal stress on the microstructure and phase transformation behavior of the sheet. Microhardness of the bent sheet at different position was carefully measured using a Vickers microhardness tester. Bending angle was found to vary from 0.5 degree sign to 70 degree sign under different processing conditions. The microhardness of the bend zone was found to increase (from 1.5 to 2 times) as compared to the as-received sample. The improved microhardness is attributed to grain refinement associated with rapid quenching during laser bending. Finally, the optimum processing zone for laser bending of stainless steel was derived
[en] Among the light metals, Mg and its alloys occupy a prominent position due to its low density, excellent machinability, and high specific strength. However, a relatively poor resistance to corrosion and wear are serious impediments against wider application of Mg alloys. In the present study, an attempt was made to enhance pitting corrosion resistance and microhardness of a commercial Mg alloy, MEZ (Zn 0.5%, Mn 0.1%, Zr 0.1%, rare earth elements 2%, Mg remaining percentage) by laser surface melting. The study included a detailed characterization of laser surface melted zone in terms of microstructure, phase analysis and its correlation with process parameters to optimize the laser processing routine. Mechanical properties like microhardness, wear, and electrochemical properties like pitting corrosion resistance of the surface melted layer were studied in detail. Microhardness of the laser surface melted layer was improved to 85-100 VHN as compared to 35 VHN of the as-received MEZ. Pitting corrosion resistance of the laser surface melted MEZ, significantly improved in a 3.56 wt.% NaCl solution because of grain refinement and redistribution of the intermetallic phases following rapid quenching associated with the process. The wear resistance of laser surface melted layer was also improved as compared to as-received MEZ
[en] Thorium(IV) is extracted by reversed phase extraction chromatography with high molecular weight carboxylic acid, versatic 10 as stationary phase on a column of silica gel with acetate buffer of pH 4.0 as the mobile phase. Several separations of th orium(IV) from binary, and multicomponent mixtures have been achieved by exploiting the differences in pH at which they formed the acetato complex and by using selectiv e elution. Thorium has been separated from cobalt, nickel, copper, cerium, zirconium, uranium and some rare earth elements. The method was applied to several synthetic mixtures. Break through capacity of the exchanger has been determined. (author)
[en] Zirconium (Zr) alloys are the backbone materials for thermal reactors because of their low neutron absorption cross section and in addition have suitable properties like high temperature mechanical and corrosion properties. For various structural applications, different Zirconium based alloys are used. Zircaloy-4 (Zr-4) is most commonly used as channel boxes in boiling water reactors (BWRs), intermediate grid applications in pressurized water reactors (PWRs) and in fuel cladding. Zircaloy cladding acts as a barrier between the radioactive fuel and exterior coolants. Therefore, the structural integrity of the cladding tube is extremely important in the safe operation of reactors. Efforts are being made to produce Zircaloy-4 products with better mechanical properties. Different routes of processing are involved like forging, pilgering and extrusion are developed over years in fabricating components to improve in-reactor performance. In this study, microstructure and hardness properties of electron beam welded Zr-4 was evaluated
[en] Friction Stir Processing (FSP) is a mode of surface enhancement used to improve the properties and the surface quality of the fabricated samples. The main focus of this research was to make a comparative performance assessment using economical and eco-friendly carbonaceous agro-wastes nanoparticle as reinforcement in AA7075-T651 during FSP and to determine the surface roughness and the tensile strength of the produced samples. Nanoparticles of Wood fly ash (WFA), coconut shell ash (CSA), coal fly ash (CFA), palm kernel shell ash (PKSA) and cow bone ash (CBA) were developed. The processing parameters used on the FSP machine were rotational speed of 1500 rpm, 20 mm min−1 processing speed, 3° tilt angle, and 0.3 mm plunge depth. The physical and the mechanical properties of the fabricated samples were studied. Results revealed that metal matrix composites (MMC) reinforced with WFA-NPs has the best surface integrity with the least Ra of 1.60 μm, followed by AA7075-T651/CBA-NPs with Ra value of 2.81 μm while unreinforced but processed base metal (UBM)- AA7075-T651 was the roughest with Ra value of 11.61 μm. It was further observed that UBM produced the highest ultimate tensile strength (UTS), Rm with a value of 620.9 MPa, and this also produced the highest yield strength at 0.1%, 0.2% and 0.5% off strain given the following values 599.1, 572.9 and 588.5 MPa respectively. Amongst the fabricated MMC, the one reinforced with carbonaceous CSA-NPs produced the highest UTS, Rm with 379.9 MPa while there was tie values in UTS, Rm for WFA-NPs and CFA-NPs which was 367.8 MPa and AA7075-T61/CBA-NPs gave the least value of UTS, Rm with a value 298.1 MPa. Most of the fractured surface areas of the nanocomposites are dominated by the dimples-induced transgranular agreeing with the remarkable interfacial bonding with the aluminium matrix composites. (paper)
[en] The present study concerns a detailed investigation of the microstructure, phase identity, composition, residual stress, wear and corrosion behavior of Ti, Zn and Zn + Ti coatings developed on IF steel by sputter deposition technique. A significant improvement in average microhardness (350-700 VHN) is noticed following sputter deposition compared to that of as-received IF steel (190 VHN). The highest microhardness recorded is 500 VHN for Ti, 350 VHN for Zn and 700 VHN for Ti + Zn bilayer, respectively. Improvement in surface hardness is accompanied by a marked improvement in wear resistance of the sputter-deposited surface against hardened steel ball. The corrosion rate of coated sample in 3.56 wt.% NaCl solution is marginally decreased (2.95 × 10−2 to 3.25 × 10−2 mm/year) as compared to that of as-received IF steel (3.55 × 10−2 mm/year). Ti-deposited IF steel registers the minimum corrosion rate (2.95 × 10−2 mm/year) among all the coated samples.
[en] Highlights: ► Optimization of process parameters for development of WC dispersed composite with Ni + NiCr as binder. ► Development of fine grained γ-stainless steel with the dispersion of very fine carbides (WC, W2C, M6C and M23C6). ► A significantly improved microhardness of the top surface (to 700–1350 VHN) as compared to as-received matrix (220 VHN) and its correlation with microstructures. ► Detailed microstructural evolution of the alloyed zone and its correlation with process parameters. ► Graded hardness distribution is achieved when lased with a low scan speed. - Abstract: The present study concerns a detailed investigation of the characteristics and properties of the alloyed zone formed in laser surface alloyed AISI 304 stainless steel with WC + Ni + NiCr (in the ratio of 70:15:15). Laser surface alloying has been carried out using a 5 kW continuous wave (CW) Nd:YAG laser (at a beam diameter of 4 mm), with the output power ranging from 1 to 3 kW and scan speed from 0.005 m/s to 0.1 m/s by simultaneous feeding of precursor powder (at a flow rate of 20 mg/s) and using Ar shroud at a gas flow rate of 5 l/min. The effect of laser power and scan speed on the characteristics of the surface alloyed layer (microstructures, phases and composition) and property (microhardness) have been investigated in details. Laser surface alloying leads to development of fine grained γ-stainless steel with the dispersion of WC, W2C, M6C and M23C6. The microhardness of the alloyed zone is significantly improved to a maximum value of 1350 VHN as compared to 220 VHN of as-received γ-stainless steel. The optimum parameters for laser processing were derived.
[en] In the quest to achieving a low cost of production and a cleaner environment has engendered researchers into using agricultural waste that will serve as a potential and promising alternative to metallic powders as reinforcement in metal matrix composites (MMC). On awareness of this search, palm kernel shell ash (PKSA) has been developed in this study as reinforcement particles in friction stir processing (FSP) of high strength, armour grade, AA7075-T651 aluminium matrix composites (AMC). Surface and structural integrity, friction and wear study, corrosion behaviours, tensile properties, and its fractography were investigated. Tribometer, surface roughness tester (SRT), potentiostat/galvanostat, scanning electron microscopy (SEM), Energy dispersive x-ray (EDX), x-ray Fluorescence (XRF), and x-ray Diffraction (XRD) were employed in the analysis. Corrosion behaviour was tested in 3.5% NaCl, two different loads of 20 N and 50 N were applied during wear test. Reinforcing with PKSA has greatly improved and enhanced the friction and wear properties, corrosion behavious, surface and structural integrity in the fabricated AA7075-T651/PKSA except in tensile properties in which base metal, AA7075-T651 has higher tensile strength. The details of XRD structural analysis, the morphology of worn surfaces, corroded surfaces and fractured surfaces are presented in this paper. (paper)
[en] The present study concerns development of a hard SiC dispersed composite layer on an Al substrate to improve its wear resistance property. A thin layer of SiC (dispersed in alcohol) is pre-deposited (thickness of 100 μm) on an Al substrate and laser irradiated using a high power continuous wave (CW) CO2 laser. Irradiation of the pre-deposited Al substrate leads to melting of the substrate with a part of the pre-deposited SiC layer, intermixing and rapid solidification to form the composite layer on the surface. Following laser irradiation, a detailed characterization of the composite layer is undertaken in terms of microstructure, composition and phases. Mechanical properties like microhardness and wear resistance are evaluated in detail. The microstructure of the composite layer consists of a dispersion of partially melted SiC particles in a grain refined Al matrix. SiC particles are partly dissociated into silicon and carbon leading to formation of a low volume fraction of Al4C3 phase and free Si redistributed in the Al matrix. The volume fraction of SiC is maximum at the surface and decreases with depth. The microhardness of the surface is improved by two to three times as compared to that of the as-received Al. A significant improvement in wear resistance in the composite surfaced Al is observed as compared to the as-received Al. The pitting corrosion property (in a 3.56 wt.% NaCl solution) is marginally deteriorated by laser composite surfacing