Characterisation and oxidation of LVOF sprayed Al₂O₃–40%TiO₂coating on superni 601 and superni 718 superalloys at 800 and 900°C

Abstract

Failure of components due to high temperature oxidation is the major degradation mechanism in boiler and gas turbine industries. Superalloys having superior mechanical properties and creep resistance are used in these applications but lack resistance to oxidation under aggressive environments. Protective coatings are used to improve their oxidation resistance in such applications. In the present investigation, Al 2 O 3 -40%TiO 2 coating was deposited on superni 718 and superni 601 superalloys by low velocity oxy fuel process. The as sprayed coating was characterised for microhardness, surface roughness, scanning electron microscopy and X-ray diffraction analysis. High temperature oxidation behaviour of Al 2 O 3 -40%TiO 2 coated and uncoated superni 718 and superni 601 superalloys has been evaluated at the elevated temperatures of 800 and 900uC for total duration of 50 cycles under cyclic conditions. Each cycle consisted of keeping the samples for 1 h at the elevated temperature followed by 20 min cooling in ambient air. Al 2 O 3 -40TiO 2 coating in the as sprayed condition showed the presence of Al 2 O 3 -TiO 2 , a-Al 2 O 3 , TiO 2 as the main phases. Al 2 O 3 -40%TiO 2 coating on superni 718 and superni 601 superalloys has shown a lower oxidation rate as compared to those of uncoated superalloys. However, the oxidation rate of the coating was not steady due to the occurrence of spallation/ sputtering at various stages. The coating was found adherent on the substrate superalloys throughout the study.

Erosion–corrosion behaviour of Ni–20Cr plasma coating in actual boiler environment

“…Although the superalloys have adequate mechanical strength at elevated temperatures, they often lack resistance to erosion-corrosion environments. [5][6][7][8] Nickel based alloys represent a significant part of overall thermal spray business. These materials are widely used as bond coats and top coats in a number of application requiring combination of properties, such as good wear resistance and corrosion resistance at the same time.…”

Low velocity oxy fuel spraying of hydroxyapatite coating on a multifunctional UNS S31254 austenitic stainless steel

“…The flame temperature of the LVOF gun lies in the range of 2300°C to 2500°C, far less than plasma spray and closer to the HVOF technique. [29][30][31][32] It could help minimise amorphous phases, which generally form through the plasma and HVOF spraying processes. 15,20 The power consumption of LVOF spraying (25-75 kW) is generally lower than HVOF spraying (100-270 kW) and plasma spraying (30-100 kW) and thus, is economical.…”

“…29,32 Recently, the LVOF process was used successfully to deposit alumina-titania and nickelchromium coatings. [29][30][31] However, the LVOF process has not been used to deposit hydroxyapatite coating onto UNS S31254 stainless steel. In this work, the adhesion strength, microhardness and corrosion behaviour of the LVOF sprayed hydroxyapatite coating were experimentally researched.…”