Papers by Author: Satya Prakash

Abstract: In the present work TiAlN coatings were deposited by plasma spray process as titanium aluminium based nitride (Ti, Al)N coatings possess excellent tribological behaviour with respect to metal cutting and polymer forming contacts. Three coatings of TiAlN were deposited on AISI-304 grade boiler steel substrate out of which two were thin nanocoatings deposited at different temperatures of 500°C and 200°C and one conventional coating was deposited by plasma spraying. The as sprayed coatings were characterized with relative to coating thickness, microhardness, porosity and microstructure. The optical microscopy (OM), the XRD analysis and field mission scanning electron microscope (FESEM with EDAX attachment) techniques have been used to identify various phases formed after coating deposited on the surface of the substrate. Subsequently the sliding wear behaviour of uncoated, PVD sprayed nanostructured thin TiAlN coatings deposited at 500°C and 200°C and plasma sprayed conventional coated AISI-304 grade boiler steel were investigated according to ASTM standard G99-03 using pin on disk wear test rig. Cumulative wear volume loss and coefficient of friction, μ were calculated for the coated as well as uncoated specimens for 0.5, 1 and 2 m/sec sliding velocities at a constant normal load of 10 N. The worn out samples were analysed with SEM/EDAX. Wear rates in terms of volumetric loss (mm3/g) for uncoated and coated alloys were compared. The nanostructured TiAlN coatings deposited at 500°C and 200°C has shown minimum wear rate as compared to conventional TiAlN coating and uncoated AISI-304 grade boiler steel. Nanostructured TiAlN coatings were found to be successful in retaining surface contact with the substrate after the wear tests.

Abstract: In the manuscript conventional and nanostructured nitrided coatings developed to increase hardness and to improve the wear, erosion and corrosion resistance of structural materials. Three coatings of TiAlN were deposited on AISI-304, out of which two were thin nanocoatings at different temperatures of 500°C and 200°C are developed by Oerlikon Balzer’s rapid coating system machine under a reactive nitrogen atmosphere. One conventional coating TiAl was deposited by Plasma spraying method which was post nitrided. Then the coated samples were characterized with relative to coating thickness, microhardness, porosity and structure. The XRD and SEM/EDAX techniques have been used to identify various phases formed after coating on the surface of steel.The microhardness of conventional TiAlN coating was found to be of the order of 900-950 Hv. The grain size for nanostructured TiAlN coatings deposited at 500°C and 200°C are 15nm and 14nm respectively as calculated by Sherrer’s formula from XRD plot.

Abstract: X-ray diffraction (XRD) is a versatile, non-destructive technique that reveals detailed information about the chemical composition and crystallographic structure of materials. In this work Ni-20Cr and Ni-50Cr coatings were deposited on two boiler steels namely T22 and SA 516 steel. The measurement of residual stresses of these cold sprayed coatings was done with the help of X-ray diffraction technique. This paper discussed the XRD study of the as-sprayed coatings. Further the XRD technique was used to study the uncoated and coated steels after cyclic exposure to air, molten salt [Na₂SO₄-60%V₂O₅], and actual boiler environments. The results obtained from the XRD analysis have been shown. The weight change results showed that the coated steels performed better than their uncoated counterparts which might be attributed to the formation of protective phases.

Abstract: Among the various characterization techniques, X-ray diffraction (XRD) analysis is a key method which reveals various phases and protective oxides formed on the surfaces of exposed specimens. This paper discusses the XRD study of two boiler steels, namely ASTMSAE213-T22 and SAE-347H with and without High Velocity Oxy-fuel (HVOF) spray Cr₃C₂-NiCr coating, which were exposed to air, molten salt [Na₂SO₄-82%Fe₂(SO₄)₃], and actual boiler environments. XRD analysis has been discussed and the results obtained from the analysis are shown. The performance of the steels was found to improve after the deposition of the coating, which may be attributed to the formation of protective phases.

Abstract: Degradation by high temperature oxidation and hot corrosion is the main failure mode of components in the hot section of gas turbines, boilers, industrial waste incinerators, metallurgical furnaces and petrochemical installations etc. Corrosive environment is because of the usage of wide range of fuel containing large amount of Cl and S together with the volatile alkali metals such as K and Na which leads to the degradation of material. To obviate this problem, superalloy Superco 605 has been studied in air as well as in molten salt environment at 900°C for 100cycles. Weight change measurements were taken by a digital electronic weighing balance having accuracy of 1 mg after each cycle (heating at 900°C for 1 hr. and subsequently cooling in air for 20 min.) which was used to determine the kinetics of corrosion. The oxide scales formed on the surface of the superalloy were characterized by various techniques such as FESEM, EDAX and XRD. It was found that superco 605 shows good oxidation resistance in air at 900°C but poor corrosion resistance in simulated incinerator environment.

Abstract: NiCrAlY coating system has been widely used for the advanced gas turbines to provide protection against high temperature oxidation and corrosion. Various methods have been used to develop these superalloy coatings. In present investigation, NiCrAlY superalloy coatings have been deposited on the superalloy substrate (Superni76) using commercially available NiCrAlY powder and High Velocity Oxide Fuel (HVOF) process. These coatings have been characterised in terms of their microhardness, porosity, microstructure features and surface roughness. The coatings have been oxidized cyclically (1hour heating and 20minutes cooling) in air at 900οC. The weight change curves have been plotted and the parabolic rate constant has been evaluated. The oxides formed after oxidation has been studied by using various techniques like optical microscopy, FESEM/EDAX and XRD. It has been observed Al¬2O3, NiCr2O4 and Cr2O3 formed upon oxidation of the coatings provide protection to the substrate alloy.

Abstract: Wear behavior of the HVOF deposited NiCr and Stellite-6, coatings on Fe-base alloy steel were evaluated by the pin-on-disc techniques. The coatings were significantly harder and less porous. SEM/EDAX and XRD techniques were used to analyse the worn out surface and wear debris. The Fe₂O₃ was identified as the major phase in the wear debris. The wear mechanism is mild adhesive wear in nature. The coatings protected the substrate steels against the adhesive wear significantly.

Abstract: Cr3C2- NiCr and Cr3C2- NiCr-(25) WC-Co coatings were deposited on T22 boiler steel by High Velocity Oxy-Fuel (HVOF) Technology. The coated as well as the uncoated steel samples were exposed to the actual boiler environments in a thermal power plant for 1500 hrs under cyclic conditions to evaluate their erosion-corrosion performance. Weight change measurements were taken for each sample after every 100 hrs. It has been observed that the weight change trends for coated steel with Cr3C2- NiCr and Cr3C2- NiCr-(25) WC-Co coatings followed a parabolic trend. The exposed samples were physically investigated for any macroscopic changes after each cycle of 100 hours. The uncoated steel showed blisters and spallation of its oxide scale, whereas the coated samples exhibited intact oxide scales, in general. Scanning Electron Microscopy/Energy Dispersive X-Ray Analysis (SEM/EDAX) was done to characterize morphology of the oxide scales. The protective nature of coatings has been explained based on the results of the study.