Papers by Author: Buta Singh Sidhu

Abstract: In the present investigation, 75Cr₃C₂-25NiCr coating was deposited on T91 boiler tube steel substrate by high velocity oxy-fuel (HVOF) process to enhance high-temperature corrosion resistance. High-temperature performance of bare, as well as HVOF-coated steel specimens was evaluated for 1500 h under cyclic conditions in the platen superheater zone coal-fired boiler, where the temperature was around 900 °C. Experiments were carried out for 15 cycles each of 100 h duration followed by 1 h cooling at ambient temperature. The performance of the bare and coated specimens was assessed via metal thickness loss corresponding to the corrosion scale formation and the depth of internal corrosion attack. The uncoated boiler steel suffered from a catastrophic degradation in the form of internal oxidation attack and thickness loss. The 75Cr₃C₂-25NiCr coating showed good adherence to the boiler steel during the exposures with no tendency for internal oxidation.

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: Erosion behavior of the high velocity oxy fuel (HVOF) deposited Cr₃C₂-NiCr and WC-Co coatings on boiler tube steels was evaluated. The solid particle erosion study was conducted, using an air jet erosion test rig at a velocity of 26 m/s and impingement angles of 30⁰ and 90⁰, on uncoated as well as HVOF spray coated boiler tube steels at 250°C. The coatings are significantly harder than the substrate steel and less porous. Scanning electron microscopy (SEM) technique was used to analyze the eroded surface. Mass loss of the coatings was found higher than the boiler tube steel.

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.