Mechanical and microstructural characterisations of NiCrCoAlYTa coatings on superalloys deposited by detonation gun technique

Abstract

The microstructure and mechanical properties of detonation gun sprayed NiCoCrAlYTa alloy coatings on the selected superalloys were investigated. The coatings were characterised in relation to thickness, porosity, microhardness, microstructure, compositions, and phases across by using the techniques such as optical microscopy, X-ray diffraction, field emission scanning electron microscopy/energy dispersive analysis and X-ray mapping. The formation of spherical or elliptical shaped dendritic splats was observed in the as sprayed coatings on the superalloys. The splat morphology of the coatings is due to the deposition and re-solidification of successive molten or semimolten powder particles. The coatings showed a bond strength of 50 MPa and the surface roughness (arithmetic average height) of the coatings was found to be in the range of 6?25-7?48 mm. The porosity and microhardness of the coatings were less than 0?48% and 385-748 Hv respectively. The XRD analysis of the coatings showed the phases c-Ni or c9-Ni 3 Al and b-NiAl inter metallic as the minor phase. 7 Cross-section morphology of NiCoCrAlYTa coated superalloys in as sprayed condition and cross-section EDS line scan of a superni 75, b superni 718 and c superfer 800HKamal et al. Mechanical and microstructural characterisations of NiCrCoAlYTa coatings on superalloys Surface Engineering 2009 VOL 25 NO 4 Surface Engineering 2009 VOL 25 NO 4 6 Continued Kamal et al. Mechanical and microstructural characterisations of NiCrCoAlYTa coatings on superalloys Surface Engineering 2009 VOL 25 NO 4

High temperature oxidation studies of detonation-gun-sprayed Cr3C2–NiCr coating on Fe- and Ni-based superalloys in air under cyclic condition at 900°C

“…2b) along with EDS spectrum and EDAX elemental compositions give various phases present in the coating, which show three types of features (melted, unmelted particles and NiCr zones). During D-gun process, the incoming powder particles possess unmelted core, upon impact on the substrate, the particle freezes rapidly, the coating thus formed contains some trapped porosity where unmelted particle accumulates as reported in the literature [31][32][33] as well as in our recent publication [34]. Dense-melted chromium carbide (different size) is surrounded by NiCr specks, distributed randomly in the coating.…”