Development of Ni-Si-Nb APS Coatings for Sulfuric Acid Resistance


A highly sulfuric acid resistant Ni-Si-Nb alloy was successfully atmospheric plasma sprayed onto a variety of ferrous substrates. Spraying parameters and the use of bond coats were evaluated based on corrosion resistance, microstructure, bond strength, porosity level, abrasive wear and Knoop hardness. Immersion corrosion tests were performed in aerated 70% boiling sulfuric acid. Corrosion of both the coating and the underlying substrates were significant, with an estimated coating mass loss of 30% in the first 24 hours of testing. Tensile adhesive strengths ranged from 7 to 11 MPa. Porosities were estimated as less than 5% on flat surfaces to as high as 7% on curved surfaces. Microstructure was changed from the cast material, from a coarse microstructure of γ-Ni31Si12 phase needles in a matrix of β1-Ni3(Si,Nb) + αSS-(Ni,Si,Nb) to a fine dispersion of γ-Ni31Si12 in an αSS-(Ni,Si,Nb) matrix. Hardness was reduced to approximately 1/2 that of the cast material and wear was approximately doubled. No evidence of long-range ordered β 1-Ni3(Si,Nb) was seen in the as-sprayed material, however annealing at 600°C for 4 hours resulted in an estimated 72% ordering.

Meeting Name

3rd International Surface Engineering Congress (2004: Aug. 2-4, Orlando, FL)


Materials Science and Engineering

Keywords and Phrases

APS Coating; Aqueous Corrosion; Nickle Silicide; APS Coating; Aqueous Corrosion; Nickle Silicide

International Standard Book Number (ISBN)


Document Type

Article - Conference proceedings

Document Version


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© 2004 ASM International, All rights reserved.

Publication Date

01 Aug 2004