Resistance of zinc thermal sprayed coatings on different corrosive environments

Degradation examinations of outer surface of low-emission steam boiler evaporator tubes are presented in the paper. Metallographic evaluation of scale morphology as well as determination of chemical composition of micro sites and distribution of elements on cross-sections is reported. Water-wall tubes were exposed in steam boiler for up to two years period. Common tubes produced from 16Mo3 steel suffered sulphide and molten salts corrosions. Thermal sprayed tubes with the single layer of 70%Ni 30%Cr alloy demonstrate better corrosion resistance, but become susceptible to sulphide corrosion due to presence of internal voids and cracks. Double layer Al2O3/Ni-30Cr coatings withstood corrosion attack for more than one year of operation, and then failed due to internal heterogeneity and crack generation.

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Surface Modification of Thermal Sprayed Coatings

Thermal Spray 1996: Proceedings from the National Thermal Spray Conference ◽

10.31399/asm.cp.itsc1996p0483 ◽

1996 ◽

Author(s):

G. John ◽

T. Troczynski

Keyword(s):

Thermal Protection ◽

Sol Gel ◽

Limiting Factor ◽

Processing Temperature ◽

High Porosity ◽

Corrosive Media ◽

Major Purpose ◽

Interconnected Porosity ◽

Sprayed Coatings ◽

Thermal Sprayed Coatings

Abstract Thermal sprayed coatings are frequently used in corrosive environments, even when their major purpose is to provide wear or thermal resistance, rather than corrosion resistance. This includes Thermal Barrier Coatings (TBC), where high porosity is a desired feature to give good thermal protection. However, as this proves to be a limiting factor in the corrosion protection, a trade off is involved. This is because the interconnected porosity in TBCs allows the corrosive media to reach the coating-substrate interface, which eventually leads to delamination of the coatings. This work addresses the problem of permeability of TBCs which can lead to premature delamination due to interfacial corrosion. The coatings studied were yttria-stabilized zirconia TBCs. A simple infiltration technique has been proposed using sol-gel ceramic precursors. The precursors studied include aluminum isopropoxide or pre-hydrolyzed ethyl silicate, which decomposed to alumina and silica respectively, at surface heat treatment temperatures as low as 550°C. In addition to sealing the surface, it is believed that some level of compressive stress is generated on the surface of TBCs on cooling from the processing temperature. Electrochemical tests in 3.0% NaCl have been carried out to study the effectiveness of the sealant. These potentiodynamic tests as well as permeability tests show a considerable decrease in interconnected porosity with sol-gel modifications of the coatings.

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Application of Plane Fractal Geometry to Adhesion Strength of Thermal Sprayed Coatings

Thermal Spray 2000: Proceedings from the International Thermal Spray Conference ◽

10.31399/asm.cp.itsc2000p1071 ◽

2000 ◽

Author(s):

S. Amada ◽

T. Hirose

Keyword(s):

Cross Section ◽

Fractal Geometry ◽

Surface Characteristics ◽

Ceramic Coatings ◽

Average Surface Roughness ◽

Roughened Surface ◽

Fractal Characteristics ◽

Sprayed Coatings ◽

Thermal Sprayed Coatings ◽

Height Data

Abstract Adhesion of ceramic coatings considerably depends on the surface characteristics of blasted substrates. The roughened surfaces have two kinds of topographical characteristics, one is of their cross section and the other is of planar. The roughened surfaces is generated by angled grit-blasting process which can be expected to improve the adhesion of ceramic coatings. The topography of the roughened surfaces has fractal characteristics in their cross section and has been more effectively related to the adhesive strength of ceramic coatings than average surface roughness traditionally used. This paper presents that fractal characteristics is evaluated in the planar topography of the blasted surfaces and shows that the planar fractal characteristics is closely related adhesion of ceramic coatings. The planar fractal dimension is evaluated by SIA (Slit Island Analysis) which needs the height data on the roughened surface. Those data are obtained by a laser-microscope in confocal type.

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Cavitation Resistant Thermal Spray Coatings on Diesel Engine Parts

Thermal Spray 2000: Proceedings from the International Thermal Spray Conference ◽

10.31399/asm.cp.itsc2000p1127 ◽

2000 ◽

Author(s):

Y. Borisov ◽

V. Bogush

Keyword(s):

Nickel Alloys ◽

Cavitation Erosion ◽

Thermal Spraying ◽

Spray Coatings ◽

Steel Wires ◽

Mechanical Mixtures ◽

Cored Wires ◽

Sprayed Coatings ◽

Spraying Method ◽

Thermal Sprayed Coatings

Abstract This work is devoted to the study of peculiarities of thermal sprayed coatings behavior under conditions of cavitation, as well as the elaboration of compositions of cavitation-resistant coatings and technology for their application with the aim of engine cylinders sleeves protection from cavitation-erosion destruction. The methods of arc metallization, flame and plasma spraying were used for coatings deposition. Powders of metal alloys and oxides, mechanical mixtures of nickel alloys with carbides, wires and flux-cored wires were applied as materials for thermal spraying. Method of magneto-striction vibration was used to determine the coatings cavitation resistance. A correlation between a bond strength of coatings and the character of their cavitation destruction was established. The best results were obtained in the case of using stainless steel wires and flux-cored wires using. Resistance of coated diesel engines sleeves was increased 1.6 times in comparison with sleeves without coatings. Semi-automatic line for arc metallization of diesel sleeves with a production of 600,000 sleeves per year was designed, build up and put into operation.

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