Erosion-corrosion behaviour of high-velocity oxy-fuel Ni-Cr-Mo-Si-B coatings under high-velocity seawater jet impingement

Abstract In this paper, erosion–corrosion characteristics of self-fluxing Ni–Cr–Mo–Si–B coatings deposited onto carbon steel (BS970 EN8) and stainless steel (UNS S31603) substrates using a commercial high-velocity oxy-fuel (HVOF) thermal spray process are reported. The coatings were studied in as-sprayed, vacuum-sealed (by polymer impregnation) and vacuum furnace fused conditions. In addition, comparisons of the HVOF coatings were made with an uncoated wrought stainless steel (UNS S31603). The erosion–corrosion characteristics were assessed under the influence of a high-velocity single-phase artificial seawater jet (without added solids), impinging perpendicularly onto the coating surface at 72 ms−1 flow velocity. Anodic polarisation tests were performed at both 18 and 50 °C to assess the in situ corrosion performance. Using static seawater results as a reference, the effects of the impinging flow on both the electrochemical response and the damage mechanisms are discussed in this paper. The application of cathodic protection (CP) reduced the extent of deterioration. The study showed the effect of sealing by polymer impregnation did not significantly alter the erosion–corrosion behaviour of the sprayed coating. However, there was an improvement in erosion–corrosion durability afforded by the post-fusion process. The mechanisms by which the improved performance of fused coatings is achieved are discussed.

[1]  A. Neville,et al.  An analysis of environmental factors affecting corrosion behavior of thermal spray cermet coatings , 1998 .

[2]  A. Neville,et al.  Degradation mechanisms of Co-based alloy and WC metal–matrix composites for drilling tools offshore , 2003 .

[3]  R. Bhagat,et al.  Tribological performance evaluation of tungsten carbide-based cermets and development of a fracture mechanics wear model , 1996 .

[4]  Tor Gunnar Eggen,et al.  Erosion and corrosion properties of WC coatings and duplex stainless steel in sand-containing synthetic sea water , 1995 .

[5]  K. Kembaiyan,et al.  Combating severe fluid erosion and corrosion of drill bits using thermal spray coatings , 1995 .

[6]  A. Neville,et al.  An examination of the electrochemical characteristics of two stainless steels (UNS S32654 and UNS S31603) under liquid–solid impingement , 2004 .

[7]  A. Neville,et al.  Mechanisms of erosion-corrosion on a cobalt-base alloy and stainless-steel UNS S17400 in aggressive slurries , 2001 .

[8]  J. Martín,et al.  Slurry erosion behaviour of thermally sprayed WC-M coatings , 1995 .

[9]  T. Hodgkiess,et al.  The effect of post-treatment of a high-velocity oxy-fuel Ni-Cr-Mo-Si-B coating part 2: Erosion-corrosion behavior , 2001 .

[10]  A. Neville,et al.  An electrochemical and microstructural assessment of erosion–corrosion of cast iron , 1999 .

[11]  A. Neville,et al.  Assessment of electrochemical response from high alloy stainless steels during slurry impingement and single impacts to improve understanding of erosion–corrosion , 2002 .

[12]  K. Bremhorst,et al.  Erosion-corrosion due to inclined flow into heat exchanger tubes , 1996 .

[13]  A. Neville,et al.  Electrochemical and mechanical interactions during erosion–corrosion of a high-velocity oxy-fuel coating and a stainless steel , 1999 .

[14]  A. Ronold,et al.  Sand erosion of wear-resistant materials : erosion in choke valves , 1995 .

[15]  A. Neville,et al.  Corrosion behaviour and microstructure of two thermal spray coatings , 1996 .

[16]  G. L. Kutner,et al.  HVOF-spray technology : poised for growth , 1991 .