Search

High-temperature corrosion of coal-fired boiler parts such as water walls and superheated tubes poses a serious threat to the efficiency of the thermal power plant. To overcome this, numbers of cor...

The present study investigates the high-temperature corrosion behavior of plasma-coated boiler steel for 1000 h in a 110-MW water tube boiler, which had encountered severe corrosion and the tube failure. The coating was carried out by alumina and MWCNTs (multiwalled carbon nanotubes)-reinforced alumina composite powders. The uncoated and coated steel substrates were hung at a platen superheater at 900 °C. After the exposure, thermogravimetric analysis was carried out to evaluate the kinetics of corrosion. XRD, SEM, TEM and EDS analysis was carried out to evaluate the corrosion products at the end of the cyclic high-temperature corrosion. The present research work concludes that CNT-reinforced alumina coatings (4.0 wt.% CNT + Al2O3 coating) have decreased the corrosion rate to 30.72 mpy, which was 113.53 mpy for conventional alumina coatings and 376.96 mpy for bare T11 boiler steel in the boiler environment. This manuscript submits the failure of tube at the platen superheater, exposure conditions and the analysis of the coated and uncoated samples of the steel tubes.

The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel (HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y (80wt%; microsized)-silicon carbide (SiC) (20wt%; nano (N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900°C for 50 cycles in Na2SO4-60wt%V2O5 molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction, field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than 2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y-20wt%SiC (N) composite coating was more effective than the Ni-22Cr-10Al-1Y coating against corrosion in the high-temperature fluxing process.

In the present research, the high temperature oxidation behaviour of Wire Arc sprayed Ni-5Al coating on T-11 and Gr-A1 boiler steels was studied at 9000C for 50 cycles. Each cycle consisted of 1 hour heating at 9000C followed by 20 min of cooling in air at room temperature. The kinematics of oxidation was established using weight change measurements for the bare and coated boiler steels. The oxidized samples were characterized using XRD, SEM/EDS, X-Ray mapping analyses. The coating was found to offer excellent oxidation resistance to the base steels. This may be attributed to the formation of strong protective chromium aluminium oxide phases.

In this investigation the basic in-vitro assessment of substrate (Ti-6Al-4V), as-deposited and heat treated reinforced HA coatings has been performed to evaluate the biocompatible conduct of these bio-ceramic coatings. Briefly adherent fibroblast cell lines NIN3T3 and non-adherent human peripheral blood monocyte cells (hPBMCs) were utilized to survey the surface biocompatibility utilizing standard MTT, trypan blue tests while their reactive oxygen species profiling was done to comprehend the potential pressure that may hamper the human cell working. The outcomes demonstrated that the as-deposited and heat treated coatings displayed incredible cell reasonability for hPBMCs and NIN3T3 cells in contrast with bare substrates. Comparative results were observed for trypan blue dye exclusion assay. Besides, oxygen free radical levels demonstrated that there is no change in reactive oxygen species (ROS) levels in cells cultured on heat treated coatings. This suggests the materials utilized in coatings are not cytotoxic in nature and the phenomenon was true both for cell lines just as human primary cells. By and large natural assessment showed that coatings are protected to human cells in essential conditions.

In present study, the high temperature oxidation behavior of HVOF sprayed NiCrAlY alloy coating and NiCrAlY–20SiC composite coating on T-91 boiler tube steel has been investigated at elevated temperature of 900°C for 50 cycles. The kinetics of oxidation has been established with weight change measurements. Both coatings and uncoated material obeyed the parabolic law during oxidation studies. XRD, FE-SEM along with EDS, X-ray Mapping characterization tools were utilized to check phase formation, elemental distribution and microstructure. The study resulted that both coatings performed better in oxidizing environment due to the formation of protective oxides in coated surface, however in case of uncoated steel unprotective Fe2O3 oxide was formed which led to extensive spallation. Moreover the composite NiCrAlY–20SiC coating provided more resistance to high temperature oxidation than NiCrAlY alloy coating.

Solid particle erosion studies were conducted in simulated coal-fired boiler environment in order to compare the erosion behavior of three different types of detonation gun (D-Gun)-thermally-sprayed coating powders, i.e., WC-12%Co, Cr3C2-25%NiCr and Al2O3-13%TiO2 on ASTM A36 steel and bare ASTM A36 steel. Erosion studies were conducted by using an air jet erosion test rig at impact angles of 45°, 60° and 90°. During the erosion studies, weight loss and erosion rates in terms of volume loss (mm3/g) were determined by using an optical profilometer. WC-12%Co-coated specimens exhibited the behavior closer to the behavior of ductile materials, whereas Cr3C2-25%NiCr- and Al2O3-13%TiO2-coated specimens exhibited the typical behavior of brittle materials. All the three different types of D-Gun-sprayed coating powders had successfully protected the ASTM A36 steel from solid particle erosion at an impact angle of 45°. Out of the three different types of coatings, two coatings, i.e., WC-12%Co and Cr3C2-25%NiCr, had successfully protected the ASTM A36 steel from solid particle erosion at impact angles of 60° and 90°. This paper evaluates the solid particle erosion behavior of bare and coated ASTM A36 steel which will be helpful in choosing the suitable coating for induced draft fan applications.

PurposeThis paper aims to perform the solid particle erosion studies in simulated coal-fired boiler conditions with a view to compare the erosion behavior of two different types of detonation gun (D-Gun) sprayed cermet coating powders, that is, WC-12%Co and Cr3C2-25%NiCr on ASTM A36 steel and bare (uncoated) ASTM A36 steel.Design/methodology/approachErosion studies were performed using an air jet erosion test rig at impingement angles of 45°, 60° and 90°. During the erosion studies weight loss, erosion rates in terms of volume loss (mm3/g) and measurement of erosion profiles were determined using optical profilometer.FindingsBoth cermet coatings had successfully protected the ASTM A36 steel from erosion at impingement angles of 45°, 60° and 90°. In the case of bare ASTM A36 steel, the erosion rates were maximal at an impingement angle of 45° and minimal at an impingement angle of 90°, thus depicting the peculiar erosion behavior of ductile materials. WC-12%Co coated specimens exhibited erosion behavior that is closer to the behavior of ductile materials. Cr3C2-25%NiCr coated specimens exhibited the maximum erosion rate at an impingement angle of 90° and minimum at an impingement angle of 45°, hence depicting the typical behavior of brittle materials.Practical implicationsIt is expected that these results will contribute to the improvement of erosion resistance of induced draft fans, by the application of D-Gun sprayed WC-12%Co and Cr3C2-25%NiCr cermet coatings.Originality/valueThis paper evaluates the solid particle erosion behavior of bare and cermet-coated ASTM A36 steel which will be helpful in choosing the suitable cermet coating for induced draft fan applications.

In the current study, friction welding of two different steels, namely low alloy steel and austenitic stainless steel was done. For conducting welding, an in-house experimental set-up was designed and fabricated. The steels were friction welded by using various axial pressures at a uniform circular speed. Influence of axial pressure on the joint strength of the friction welded specimens such as tension, impact toughness, torsion strength and microhardness were evaluated. Moreover, the weldments were also tested for high temperature corrosion resistance. The corrosion testing of the welded joints was carried out in a molten salt environment of Na2SO4 + V2O5 60% at 650°C. Weight change data were used to establish the kinetics of corrosion. Based upon this data, the weldments showing best corrosion resistance was identified. Subsequently to understand the composition of oxide scale, the specimen was evaluated using SEM/EDS and X-ray diffraction techniques.

Hardfacing is one of the adaptable methods that can build up the hard and wear resistant surface layer of different materials on the surface of substrate material. It helps them withstand wear, as well as prevent corrosion and high temperature oxidation. In the present investigation three different types of Fe–C–Cr based hardfacing electrodes with varying chemical compositions were deposited on ASTM A36 steel substrate by using manual metal arc welding (MMAW) process. ASTM A36 steel was selected as a base material after consulting with Pressure and Process Boilers, Saharanpur (India), which is a leading manufacturer of boilers. ASTM A36 steel is mostly used by this company for the production of induced draft fans. MMAW process with direct current constant current type power source was used to deposit the hardfaced layers of uniform quality. Straight polarity was used for MMAW process so that more of the arc heat should be concentrated on the electrode. The hardfaced samples were characterized using various characterization techniques and the results of the same were also outlined in the present investigation.

Purpose This paper aims to discuss that a conventional Al2O3, 1.5 Wt.% carbon nanotubes (CNTs)-Al2O3, 2 Wt.% CNTs-Al2O3 and 4 Wt.% CNTs-Al2O3 composite coatings were deposited with the help of Plasma spray process. Design/methodology/approach To better understand the effect of CNT reinforcement on oxidation resistance, high-temperature oxidation behaviour of conventional Al2O3, 1.5 Wt.% CNTs-Al2O3, 2 Wt.% CNTs-Al2O3 and 4 Wt.% CNTs-Al2O3 composite coatings at 900°C was compared with the performance of the uncoated ASME-SA213-T11 boiler tube steel substrate. Findings The results showed that the CNT-reinforced alumina coatings exhibited better oxidation resistance and thermal stability than uncoated ASME-SA213-T11 boiler tube steel. The coated steel substrates had a lower mass gain rate than the substrate after different oxidation times. Originality/value Limited literature is available where the CNT have been reinforced into the composite alloy powders and has been thermally spray-deposited for various surface engineering applications. This research showed that with the increase in the percentage of CNTs into the alloy powder mixture, there is a significant reduction in weight gain and hence higher resistance to oxidation.

The biocompatible CaP-based coatings are deposited on the bio-materials to improve the metallurgical, mechanical and biological behaviour of medical implants in body fluid environment. Besides, these biocompatible coatings are capable to prevent the leaching of toxic ions from metal to the surrounding body environment and further their porous structure provides good osseointegration. However, in spite of these benefits, it always remains a challenge for the researchers to optimise the various properties of CaP-based coatings which finally affect their clinical performance. To achieve this, several post coating techniques have been developed. Post coating heat treatment is one of the posts coating technique which has been widely investigated by the researchers since last three decades. This review explores the impact of post coating heat treatment on the microstructural, mechanical, electro-chemical corrosion and in-vitro behavior of hydroxyapatite coatings.

The present investigation discusses the hot corrosion behavior of AlCrN and TiAlN nano-coatings on T91 boiler steel by PAPVD process subjected to molten salt of Na2SO4-60%V2O5 at 900 °C for 50 cycles. Surface and cross-sectional studies were performed by AFM, SEM/EDS and XRD techniques to understand the corrosion kinetics and mechanism. T91 bare boiler steel as well as TiAlN-coated specimen has shown higher internal oxidation as well as weight gain. The better corrosion resistance of AlCrN-coated specimen has been observed by virtue of higher availability of Cr and Al in the oxide scale as well as adherent and dense coating. The betterment of AlCrN coating can be attributed to low internal oxidation as well as movement of Cr and Al toward oxide scale to form protective corrosion barriers.

The aim of this present work was to deposit reinforced hydroxyapatite coatings with a bond coat of zirconia on Ti-6Al-4V substrate using the vacuum plasma spray technique in order to improve the surface properties. To achieve that, HA + 10 wt% Al2O3 and HA + 10 wt% ZrO2 coatings with an intermediate layer of zirconia were deposited on Ti-6Al-4V implant substrate. Further, these coatings were subjected to post-coating heat treatment at 700 °C for 1 h. The morphology and phase analysis of bio-ceramic powders, as-sprayed and heat-treated coatings, have been characterized using a scanning electron microscope and an X-ray diffractrometer. Crystallinity, surface roughness, porosity, hardness and shear strength were also investigated. The wear behaviour of the coatings was evaluated using a Taber abrasion tester as per ASTM F1978 standard. The results indicate that heat-treated coatings exhibit lower wear resistance than as-sprayed coatings and show lower porosity and higher crystallinity and hardness after heat treatment. Slight improvement in shear strength was observed after heat treatment.

In this research work, carbon nanotube (CNT)-reinforced Al2O3 coatings were prepared and successfully deposited on ASME-SA213-T11 boiler tube steel. Coatings were deposited by the plasma spray process. Ni-Cr was also used as a bond coat before applying CNTs-Al2O3 coatings. The coatings were subjected to metallography, XRD, SEM/EDAX, and X-ray mapping analysis. The porosity of CNT-Al2O3 mixed coatings was decreasing with increase in CNT content. The CNTs were found to be uniformly distributed within the Al2O3 matrix. The CNTs were chemically stable during the spray forming. It did not react to form oxides or aluminum carbides even at the very high processing temperature.

Two reinforced hydroxyapatite (HA) coatings with an intermediate layer of zirconia were deposited on Ti–6Al–4V by vacuum plasma spray (VPS) technique. In first coating, HA was reinforced with 10 wt % Al2O3 whereas in second coating, HA was reinforced with 10 wt % ZrO2. The objective of this study was to investigate the microstructure, phase formation and mechanical properties like hardness and bond strength of as-sprayed coatings and the coatings after post coating heat treatment at 700 °C for 1 h. The characterization of the coatings was performed by using SEM/EDAX, XRD, porosity, crystallinity and roughness measurement. The coatings were also evaluated for mechanical properties like hardness and tensile bond strength. It was observed that after post coating heat treatment, crystallinity increased and porosity decreased which indicated recrystallization of amorphous phases of as-sprayed coatings. Heat treatment resulted into improvement in cross-sectional hardness, however sharp decrease in bond strength was observed.

The failure analysis of the damaged surfaces is crucial for the selection of most expedient process and processing parameters leading to longer mean time between failures. Many procedures are being developed and deployed to determine the kind and severity of failure and to prevent the hot forging die failure. In spite of all these efforts, the losses still occurred in terms of profitability. However, there is no comprehensive review of failures of hot forging dies, to examine and understand their current research status to solve the failure problem, has been done. Here, an updated review of various kinds of failures and their causes has been presented in general. The goal of this paper is to communicate an updated perspective of kind of failures such as wear (Abrasive and Adhesive), plastic deformation, fatigue (thermal and mechanical) occurs due to high thermal combats, mechanical strain, whorled loading and corrosion while hot forging process. The paper will help the better understanding of directions in which research of failure analysis has been done relevant to the hot forging industries and will assist in the prevention/prolongs of die failure.

In the present study, reinforced hydroxyapatite (HA) coatings (HA + 10 wt% Al2O3 and HA + 10 wt% ZrO2) were deposited on SS-316 L substrate with an intermediate layer (bond coat) of zirconia by vacuum plasma spray technique. The so-formed reinforced HA coatings were heat treated at 700 °C for 1 h. The influence of post coating heat treatment on phase composition, microstructure, mechanical and electrochemical corrosion properties were investigated. As-sprayed and heat treated coatings were characterized by x-ray diffraction, scanning electron microscope, surface roughness, porosity and crystallinity. Results showed that after post coating heat treatment, the structural integrity of HA has been completely re-established. Moreover, significant drop in porosity has been observed due to the sintering effect produced by heat treatment. Considerable improvement in nanohardness and shear strength was witnessed; however, the nanohardness of top layer was decreased after annealing due to the weak bonding of partially melted and un-melted particles with fully melted splats caused by diffusion process. As-sprayed coatings exhibited higher wear resistance compared to heat treated coatings. Nevertheless, post coating heat treatment effectively enhanced the corrosion resistance of coatings, since, the heat treatment lead to densification of coatings microstructure which further reduces the active sites for dissolution.

Thermal spray coatings can be applied economically on machine parts to enhance their requisite surface properties like wear, corrosion, erosion resistance, and so forth. Detonation gun (D-Gun) thermal spray coatings can be applied on the surface of carbon steels to improve their wear resistance. In the present study, alloy powder cermet coatings WC-12% Co and Cr3C2-25% NiCr have been deposited on ASTM A36 steel with D-Gun thermal spray technique. Sliding wear behavior of uncoated ASTM A36 steel and D-Gun sprayed WC-12% Co and Cr3C2-25% NiCr coatings on base material is observed on a Pin-On-Disc Wear Tester. Sliding wear performance of WC-12% Co coating is found to be better than the Cr3C2-25% NiCr coating. Wear performance of both these cermet coatings is found to be better than uncoated ASTM A36 steel. Thermally sprayed WC-12% Co and Cr3C2-25% NiCr cermet coatings using D-Gun thermal spray technique is found to be very useful in improving the sliding wear resistance of ASTM A36 steel.

Hydroxyapatite powder reinforced individually with 10 wt percentage (wt%) of Al2O3 and ZrO2 (HA + 10 wt% Al2O3 and HA + 10 wt% ZrO2) was thermally sprayed onto SS-316L substrate with a bond coat of Zirconia by vacuum plasma spray (VPS) technique. The resulted coatings were heat treated at 700 °C for 1 h to study its effects on microstructural and mechanical properties of the deposited coatings. The characterization of the coatings was carried out using scanning electron microscope, x-ray diffraction, porosity, surface roughness and crystallinity using Rietveld analysis. The results indicated that after post coating heat treatment substantial decrease in porosity was witnessed along with significant improvement in crystallinity. Besides, the hardness across the cross-section of the coatings and bond strength was considerably improved; however the hardness of top coat was reduced owing to the loosening of un-melted and partially melted particles by diffusion process which takes place during heat treatment.

Die/tooling failure during the hot forging process is mainly due to repeated varying mechanical loads, rigorous thermal shocks, as well as strong friction and erosion. These cause different failure mechanisms, such as wear, thermal fatigue, and plastic deformation. The enhancement of die service life for a hot forging industry is necessary now in order to be competitive globally. Four nitride coatings—TiN, TiAlN, TiCrN, and AlCrN—were deposited onto plasma-nitrided AISI H21 hot work die steel using the cathodic arc evaporation physical vapor deposition technique. The coatings were characterized by scanning electron microscope (SEM), SEM–energy dispersive x-ray spectroscopy (EDS), x-ray power diffraction (XRD), line scan EDS, and x-ray mapping tests and microhardness tester. The wear characteristics were examined using a pin-on-disk method at high temperature and speed against EN31 bearing steel disk. It was observed that the AlCrN and CrTiN coatings have lower wear rates than other coatings at high temperature (550°C). Also, these coatings performed best during actual industrial practice. The enhancement in die life was reported to be 55 and 76 % in terms of parts being hot forged. The low value of the coefficient of friction for all coatings at 550°C can partly be attributed to lower hardness difference between the pins and disks, decreased plastic deformation in the contact, and, consequently, less ploughing (abrasive wear action). Predominately, wear was the main die failure mode there was; when used, dies were observed microscopically.

Agricultural waste has shown its capability to replace the conventional microwave absorbers like polyurethane and polystyrene. The cheap cost of agricultural waste microwave absorber and high reflection loss make these absorbers much more efficient and effective absorbers. In this work sugarcane bagasse are used as microwave absorber and its absorption properties are enhanced by addition of coal in it. The whole work is completed in four stages. The dielectric properties of both sugarcane bagasse and mixture of sugarcane bagasse and coal is measured and their absorption behavior is simulated using CST Microwave studio which shows the enhancement in absorptive power of sugarcane bagasse by adding coal in it. In last stage, reflection loss of fabricated structure of sugarcane bagasse and coal is measured using Network analyzer and horn antenna which confirm the ability of sugarcane bagasse and coal structure to be used as a microwave absorber in designing the anechoic chamber.

Erosion studies were performed in simulated coal-fired boiler conditions with a view to compare the erosion behaviour of two different types of detonation gun (D-gun) sprayed cermet coating powders, i.e., WC-12%Co and Cr3C2-25%NiCr on ASTM A36 steel and bare (uncoated) ASTM A36 steel. During the erosion studies weight loss, erosion rates in terms of volume loss (mm3/g) and measurement of erosion profiles were determined utilising optical profilometer. All the two different types of D-gun sprayed cermet coatings had successfully protected the ASTM A36 steel from erosive wear at impingement angles of 45o, 60o and 90o. In the case of bare ASTM A36 steel specimens the solid particle erosion rates were maximal at an impingement angle of 45o that was reduced at an impingement angle of 60o and minimal at an impingement angle of 90o that is the typical erosive wear behaviour of ductile materials. WC-12%Co coated specimens exhibited erosive wear behaviour that is closer to the behaviour of ductile materials. Cr3C2-25%NiCr coated specimens exhibited the maximum volume erosion rate at an impingement angle of 90o which was reduced at an impact angle of 60o and minimum at an impingement angle of 45o hence depicted the typical behaviour of brittle materials.