Search

The erosion behavior of three different cermet coatings namely, Al2O3, Al2O3 + 3% TiO2 and Al2O3 + 13% TiO2 was studied in order to perform erosion analysis. The coatings were sprayed using Plasma spray gun in a simulated coal-fired boiler conditions on SAE-347H steel. An optical profilometer was put to use in order to find weight loss, erosion profiles and erosion rate (mm3/g) in term of volume loss. All the Plasma gun sprayed cermet coatings were able to protect SAE-347H steel from erosive wear at incident angles of 30°, 60° and 90°. In case of uncoated SAE-347H steel specimens the solid particle erosion (SPE) rate was highest at an incident angle of 30°, nominal at incident angle of 60° and lowest at incident angle of 90°.

In the present investigation, a plasma spray process was used to deposit bi-layer NiCrAlY/ Al2O3-40%TiO2 coating powder on three substrates namely T-91, A-1 boiler steel, and Superfer800H superalloy. The deposited coating was found to be dense, and uniform with thickness ranges from 200 to 250 µm. The oxidation behavior of both (bare and coated) specimens at elevated temperatures was ascertained by using a high-temperature furnace. The experiments were conducted over 50 cycles. In each cycle, the specimens were subjected to an isothermal temperature of 900 °C for 1 h followed by cooling for 20 min at room temperature in atmospheric air. The thermogravimetric study for both (bare and coated) specimens was conducted to find the corrosion rate by calculating the parabolic rate constant of the corroded specimens. The characterizations of the coatings before and after the high- temperature oxidation tests were investigated by employing various characterizations techniques. The result showed that the Al2O3-40%TiO2 ceramic coating significantly reduced the weight gain compared with the bare substrates. The high resistance of the deposited coating against the harsh oxidizing environment was because of the occurrence of protective phase (Al2O3, TiO2, and Al2Ti7O15) in the oxide scale.

Tungsten Inert Gas (TIG) welding has been learnt to be the most widely used technique among the fusion welding techniques. Welding of different components of boilers is preferably accomplished by TIG welding, due to the process capabilities of the technique to produce sound joints, even in case of Dissimilar Metal Joints (DMJ). DMJs owing to the techno-economic advantages, find vast area of application especially in boiler fabrication industry. It has been learnt that the quality of welded joints is signified by mechanical properties of the joint. The present paper is focused on the behavioural aspects of similar and dissimilar metal joints of ASME SA 213 GR. T11 and BS 3059:1987 PT 1 ERW 320, the boiler steam tube materials, prepared by TIG welding under torsional loading. It has been observed that the dissimilar metal joint has performed better than the individual similar metal joints under torsional loading by achieving 85% of the torsion strength of one of the parent metal, whereas in the case of individual similar metal joints of ASME SA213 Gr. T11 and BS3059:1987 PT1 ERW320, 78% and 68% of the torsion strength of respective parent metals has been observed. ANOVA statistics have validated the existence of significant impact of input process variables on the output quality measure of the welded joint at 95% level of confidence. The predictive models for optimum torsional strength have been proposed by regression analysis.

Thermal spraying coating techniques have emerged as very effective surface protection technology to apply protective coatings for corrosion and wear resistance applications. These coatings have gained more importance in recent past. Advances in powder and wire production have resulted in development of various types of surface coatings with excellent wear and corrosion resistance properties. Because of excellent mechanical, thermal and electrical properties of Carbon Nanotubes, CNTs reinforced composite coatings are being developed for various applications, e.g. automotive, aerospace and sports equipment industry. It is observed that if properly deposited, these CNTs ceramic composite coatings can provide improved properties like wear and corrosion resistance. It has been found that CNTs composite coatings can be successfully deposited by thermal spraying techniques, and these coatings provide better performance than conventional coatings. This paper reviews the performance of such coatings developed by various researchers.

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 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.

Plasma spray technique is utilized to cover the Induced Draft (ID) fans with 88%WC–12%Co (wt%) powder and 87%Al2O3–13%TiO2 (wt%) powder. The material of ID fan was ASTM A36 steel (IS2062) grade. The main focus of recent study was to investigate the influence of nature and characteristics (mainly hardness, coating thickness, bond strength, and porosity). Two coating powders with dissimilar particle size and their distribution, shape, and density were sprayed by similar parameters of plasma spraying conditions. The morphology of both the coatings was investigated by Scanning Electron Microscopy, which exhibits the sub-micro and micro-sized structure, with same thickness and porosity. Very intense and consistent was obtained and the variation in precursor size does not affect the coating structure.

The present study emphasizes on joints two industrially important materials AISI 304 with AISI 1021steels, produced by friction welding have been investigated. Samples were welded under different axial pressures ranging from 75MPa to 135MPa, at constant speed of 920rpm. The tensile strength, torsional strength, impact strength and micro hardness values of the weldments were determined and evaluated. Simultaneously the fractrography of the tensile tested specimens were carried out, so as to understand the failure analysis. It was observed that improved mechanical properties were noticed at higher axial pressures. Ductile failures of weldments were also observed at 120MPa and 135MPa axial pressures during fractography analysis.

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.

Rice husk and coal is an innovation in enhancing the microwave absorption properties of pyramidal microwave absorbers to be used in radio frequency anechoic chambers. An anechoic chamber consists of radar absorbing material (RAM) along its wall; floor and ceiling to eliminate unwanted reflections to create electromagnetically quite environment. To design the pyramidal microwave absorber, coal has been added to rice husk. This innovative material combination has been investigated to determine the best reflectivity performance of pyramidal microwave absorbers. In the commercial market, polyurethane and polystyrene are the most popular foam based material that has been used in pyramidal microwave absorber fabrication. Simulation tool that has been used is CST Microwave Studio. Simulation based comparison of rice husk and combination of rice husk plus coal is done in the frequency range of 0-20 GHz. Chemicals used to intact the powdered form of rice husk and coal are polyester resin, methyl ethyl ketone peroxide (MEKP) and cobalt. Pyramidal microwave absorber has been tested using dielectric probe method and radar cross section method (RCS). Reflection loss performance is tested in the frequency range of 8.2 to 12.4 GHz.

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.

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.

This review is done essentially to study results in the field of synthesis and characterization of Carbon Nanotubes (CNT’s) reinforced nanocomposite coatings using thermal sprayed coatings. CNT reinforced nanocomposite coatings produced by thermal spray process are being developed for a wide variety of applications, e.g. aerospace, automotive and sports equipment industries. It is anticipated that, if properly deposited, nanocomposite ceramic coatings could also provide improved properties like wear resistance and thermal barrier coatings. These results clearly demonstrate that the significant improvement in coating performance can be achieved by utilizing proper thermal sprayed nanocomposite coatings. Thermal sprayed nanocomposite coatings shows improvement of resistance to wear, erosion, corrosion and mechanical properties. The purpose of this paper is to review CNT reinforced nanocomposite coatings using thermal spray by various researchers.

There has been significant increase in use of glass fibre reinforced composites as structural materials in naval mine countermeasure surface ships. Sea mines when detonated emit underwater shock waves, which could impart severe loading to naval ship structure; there are attempts to model the response of a ship structure to this loading. For the model to be accurate & useful material property data determined experimentally by taking different weight percentage of glass fibers (E-300, mat form) with epoxy resin & comparison with fly ash reinforced composite. Specimens in the form of cube of size 10X10X10 (mm’s) are used & results are presented. Fracture behaviour of composite can also be studied using SEM. SEM analysis is done to observe distribution of fly ash particles in matrix, resin fly ash interface, glass fibre matrix interface, glass fibre distribution etc,.

Metal Matrix Composites (MMCs) have evoked a keen interest in recent times for potential applications in aerospace and automotive industries owing to their superior strength to weight ratio and high temperature resistance. The widespread adoption of particulate metal matrix composites for engineering applications has been hindered by the high cost of producing components. Although several technical challenges exist with casting technology yet it can be used to overcome this problem. Achieving a uniform distribution of reinforcement within the matrix is one such challenge, which affects directly on the properties and quality of composite material. In the present study a modest attempt has been made to develop aluminium based silicon carbide particulate MMCs with an objective to develop a conventional low cost method of producing MMCs and to obtain homogenous dispersion of ceramic material. To achieve these objectives two step-mixing method of stir casting technique has been adopted and subsequent property analysis has been made. Aluminium (98.41% C.P) and SiC (320-grit) has been chosen as matrix and reinforcement material respectively. Experiments have been conducted by varying weight fraction of SiC (5%, 10%, 15%, 20%, 25%, and 30%), while keeping all other parameters constant. The results indicated that the ‘developed method’ is quite successful to obtain uniform dispersion of reinforcement in the matrix. An increasing trend of hardness and impact strength with increase in weight percentage of SiC has been observed. The best results (maximum hardness 45.5 BHN & maximum impact strength of 36 N-m.) have been obtained at 25% weight fraction of SiC. The results were further justified by comparing with other investigators.

Al–SiC composites containing four different weight percentages 5%, 10%, 20% and 25% of SiC have been fabricated by liquid metallurgy method. Friction and wear characteristics of Al–SiC composites have been investigated under dry sliding conditions and compared with those observed in pure aluminium. Dry sliding wear tests have been carried out using pin-on-disk wear test rate normal loads of 5, 7, 9 and 11 Kgf and at constant sliding velocity of 1.0m/s. Weight loss of samples was measured and the variation of cumulative wear loss with sliding distance has been found to be linear for both pure aluminium and the composites. It was also observed that the wear rate varies linearly with normal load but lower in composites as compared to that in base material. The wear mechanism appears to be oxidative for both pure aluminium and composites under the given conditions of load and sliding velocity as indicated by scanning electron microscope (SEM) of the worn surfaces. Further, it was found from the experimentation that the wear rate decreases linearly with increasing weight fraction of silicon carbide and average coefficient of friction decreases linearly with increasing normal load and weight fraction of SiC. The best results have been obtained at 20% weight fraction of 320 grit size SiC particles for minimum wear.

Austempered Ductile Iron (ADI) can be as twice as strong as standard spheroidal iron at the same level of toughness. It responds to work-hardening surface treatments and exhibits excellent fatigue and wear property. There is extensive work done on the fracture of steel with ferrite or/and austenite structure, but little on fracture behaviour of ADI whose microstructure also comprises austenite and ferrite but with graphite nodules in the matrix. The present work is aimed in this direction. The fracture behavior of Ni-Mo ADI is studied. It is found that the crack always originates from graphite nodules and the matrix affects the propagation path.

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.

The aim of the present study was to investigate the effect of axial pressures on the mechanical properties of friction welded AISI 304 with AISI 1021 steels, produced by mechanical joining. In the present study, an experimental setup was designed in order to accomplish friction welded joints between austenitic stainless steel and low alloy steel. Samples were welded under different axial pressures, at a constant speed of 800 rpm. The tensile strength, impact strength, and microhardness values of the welded joints were determined and evaluated and on the basis of the results obtained from the experimentation, the graphs were plotted.