Cavitation- and erosion-resistant thermal spray coatings

Original publisher: [Champaign, IL] : US Army Corps of Engineers, Construction Engineering Research Laboratories ; [Springfield, VA : National Technical Information Service, distributor, 1997] OCLC Number: ocm40505648 Subject: Protective coatings. Excerpt: ... 15 USACERL TR-97 / 118 Corrosion Corrosion occurs by an electrochemical process. Two dissimilar metals ( forming an anode and a cathode ), an electrolyte, and an electrical circuit connecting them are required for corrosion. Dissolution of the metal into the electrolyte occurs at the anode. Cavitation may combine with corrosion to create much greater damage rates than the sum of the two if each acted alone. Metals usually develop passive films or layers on the surface that inhibit further corrosion and metal removal. Cavitation removes this passive film exposing a fresh metal surface that can readily corrode. The increased surface roughness caused by corrosion may also promote cavitation ( Rodrigue 1986 ). Weld Repair Techniques available for cavitation damage repair including: ( 1 ) weld overlays and inlays, ( 2 ) reinforced epoxy coatings, and ( 3 ) thermal spray coatings. Of these methods, the one most commonly used is the weld overlay because it produces the most durable coating. Two weld repair processes generally used for cavitation repair are: ( 1 ) gas metal arc welding ( GMAW ) or metal-inert gas ( MIG ) welding, and ( 2 ) shielded metal arc welding ( SMAW ) or stick electrode welding ( Rodrigue 1986 ). Due to the condition of most cavitated surfaces, damage generally cannot be repaired by directly filling the pitted areas. The pitted surface is usually undercut to remove the damaged area and to provide a surface that can be adequately cleaned before filling repair. The resulting space is normally filled by welding with a common stainless steel alloy such as 308L or 309L. The top 0.25 in. layer is usually 308L stainless steel. 309L stainless steel is used when the first pass is on mild steel. 30...