Salt fog corrosion behavior of high-velocity oxygen-fuel thermal spray coatings compared to electrodeposited hard chromium

The corrosion behavior of several coating/substrate combinations was determ ined using the ASTM B117 Salt Fog Test. The coatings were electrodeposited hard chromium (EHC) and two high-velocity oxygen-fuel (HVOF) thermal-spraye d coatings, tungsten-carbide/cobalt (WC/Co) and Tribaloy 400 (T400). The su bstrates were 4340 steel, 7075 aluminum alloy, and PH13-8 stainless steel. On the 7075 Al alloy, a sulfamate nickel layer was deposited prior to the d eposition of hard chromium. The results indicated that on the 4340 steel no ne of the coatings provided significant protection, with equivalent perform ance between the EHC and WC/Co coatings and slightly poorer performance for the T400. On the 7075 Al alloy, the EHC with sulfamate nickel exhibited ex cellent performance as no pits or blisters were noted on the faces or edges of the samples. The WC/Co showed no pitting or blistering on the faces but had a significant amount of pitting along the edges. The EHC and WC/Co coa tings performed well on the 13-8 stainless steel as no pits or blisters wer e noted on the faces or edges. The T400 coatings had rust stains on the fac es and edges but defects could not be seen with the unaided eye or at a 7X magnification. (C) 2000 Elsevier Science S.A. All rights reserved.