Search

Materials are precious resources. Different methods are employed to protect the material from degradation. Thermal spraying is one of the most effective method to protect the material from wear, high temperature corrosion, stresses and erosion, thus increasing the life of material in use. Detonation gun spraying is one of the thermal spraying techniques known for providing hard, wear resistant and dense microstructured coatings. This paper summarizes the results of previous research done by various authors on different coatings done by detonation gun spraying technique.

Corrosion scales play an important role in modifying water quality in drinking water distribution systems. The corrosion scales from old water pipe lines were analyzed for their structure and composition. This paper presents the results of comprehensive study of deposits found in water distribution system of Ulhasnagar city of Maharashtra, India. Scales were investigated by XRD, FTIR, SEM and ED’s analytical techniques. It was found that goethite, magnetite, lepidocrocite, hematite and Akaganite were identified as the primary constituents of brown deposits. The corrosion scales had a shell-like, enveloping layer, covering porous deposits of iron oxide phases. Our studies were able to identify important constituents of three different pipes of water distribution systems. Akaganite was found to be present in chloride environment. Along with iron hydroxide phases it was found that corrosion product also contain some organic matter which may be due to adsorption of biofilm on the surface of pipe. Further studies are needed to establish the role of corrosion scales in the mechanism of iron release from corroded pipes.

In this work, TiAlN and AlCrN coatings were deposited on ASTM-SA213-T-22 boiler steel using Balzer’s rapid coating system (RCS) machine (make Oerlikon Balzers, Swiss) under a reactive nitrogen atmosphere. Cyclic oxidation studies in molten salt environment were conducted at 900°C temperature in the laboratory using silicon carbide furnace. The weight gain was measured after each cycle and visually examined the surface morphology of the oxidized samples was studied using FE-SEM with EDAX attachment and XRD analysis. The results obtained showed the better performance of TiAlN coated T-22 boiler steels than the AlCrN coated and uncoated T-22 boiler steel.

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,.

The oxidation behaviour of T-91 steel and T-22 steel in air has been studied under isothermal conditions at a temperature of 900°C in a cyclic manner. Oxidation kinetics was established for the T-91 steel and T-22 steel in air at 900°C under cyclic conditions for 50 cycles by thermogravimetric technique. Each cycle consisted of 1 hour heating at 900°C followed by 20 min of cooling in air. T-91 steel sample followed somewhat linear rate of oxidation while T-22 sample followed the parabolic rate law of oxidation. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray (SEM/EDAX) techniques were used to characterise the oxide scales. T-91 steel was found to be more corrosion resistance than T22 steel in air oxidation for 50 cycles.

Metals and alloys gets oxidized when exposed to elevated temperatures in air or highly oxidizing environments, such as combustion gas with excess of air or oxygen. They often rely on the oxidation reaction to develop a protective oxide scale to resist corrosion attack. In the present study, nanostructured TiAlN and AlCrN thin films were deposited by physical vapour deposition process on T-22 boiler steel (ASTM-SA213-T-22). Cyclic oxidation studies in air were conducted at 900°C temperature in the laboratory using silicon carbide furnace. The weight gain was measured after each cycle and visually examined the surface morphology of the oxidized samples was studied using FE-SEM with EDAX attachment and XRD analysis. The results obtained showed the better performance of AlCrN coated T-22 boiler steels then the TiAlN coated and uncoated T-22 boiler steel.

The oxidation behaviour of T-91 steel and T-22 steel in salt of 75wt.% Na2SO4+25wt.% NaCl has been studied under isothermal conditions at a temperature of 900°C in a cyclic manner. Oxidation kinetics was established for the T-91 steel and T-22 steel in salt at 900°C under cyclic conditions for 50 cycles by thermogravimetric technique. Each cycle consisted of 1 hour heating at 900°C followed by 20 min of cooling in air. Both the samples nearly followed the parabolic rate law of oxidation. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray (SEM/EDAX) techniques were used to characterise the oxide scales. T-91 steel was found to be more corrosion resistant than T-22 steel under salt oxidation.

In this work, TiAlN and AlCrN coatings were deposited on Superfer 800H superalloy using Balzer’s rapid coating system (RCS) machine (make Oerlikon Balzers, Swiss) under a reactive nitrogen atmosphere. The corrosion resistance of the substrate, TiAlN and AlCrN coated samples in a 5 wt% NaCl solution was evaluated and compared by salt fog (spray) test for 24 hrs, 48 hrs and 72 hrs. The samples were monitored and analyzed by using weight loss measurement, XRD and SEM/EDAX techniques. There was no weight loss observed for coated as well as uncoated specimens in all test conditions.

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.

Nitrided coatings have been used to increase hardness and to improve the wear and corrosion resistance of structural materials. In this work, TiAlN and AlCrN coatings were deposited on Superfer 800H (INCOLOY 800 H) substrate by using Balzer’s rapid coating system (RCS) machine (make Oerlikon Balzers, Swiss) under a reactive nitrogen atmosphere. The coated samples were subjected to optical microscopy (OM), XRD analysis, Field emission scanning electron microscope (FESEM with EDAX attachment), AFM analysis. The corrosion resistance of the substrate, TiAlN-coated and AlCrN-coated samples in a 3 wt% NaCl solution was evaluated and compared by electrochemical potentiodynamic polarization method. It was found that the AlCrN-coating exhibited better corrosion resistance.

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.