Production methods of thermal spraying ceramic coating materials

Ceramic materials are brittle, basically preparation of coating with thermal spraying technique in powder form, mechanical process and physical-chemical process are the two main ways to preparation of thermal spraying ceramic coating powder materials. Mechanical process includes crushing method，atomization method, mixing method, mechanical Alloying and so on, and physical-chemical process contains bonding process, chemical reduction method, pyrolysis method, quench method, combustion method etc. . liquidity and shape pf powder, apparent density, sedimentation efficiency and other wholesomeness are affected by the preparation way of ceramic powder, so it’s have great influence on thermal spraying process performance.

Except powder form of thermal spraying powder ceramic coating materials, the other form is composite wire which contains ceramic particles, it mainly includes filling composite wires and flexible composite wires. The former is made of mixing, heating, squeezing of ceramic powder and seldom adhesives. Common coating metal materials of Metal filling materials composite wire are Ni, Cu, Al, steel, stainless steel and so on,  common ceramic particles are WC, Al2O3, TiO2, Cr2O3 etc.

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Applications of thermal technique in energy industry

In china, coal are the main fuel of power plant boiler and industrial boiler. “four tubes” of boiler work under bad environment of high temperature, high pressure, gas corrosion and grains ablation, high temperature corrosion and abrasion generate easily, then thinning the wall tubes, leading to damage of equipment even accidents. The surface of Induced draft fan, air cylinder and some other equipment which high-speed gas flows through, abrasion, cavitation and other reasons may lead to efficacy loses, causing heavy losses. Many moving parts (for example, axle), scraped because of mechanical abrasion. In addition, electric power transmission & transformation equipment and all kinds of steel structures of power plant suffer serious industrial atmospheric corrosion because of they are always in the outdoor environment. All the solutions can be solved by thermal spray techniques, strengthening and improve its service life greatly, or restoring its workability by repairing, then increasing production safety and economic benefit of powder plant.

 

High-temperature corrosion and abrasion not only have great effects on safe operation of boiler, but also cause huge economic loss, it’s urgent to be solved in safety problem of boiler. It has been proved that spraying high chromium NiCr wire coating with arc spraying is an ideal method, which has been widely used in many countries. And except wire, powder is common used in thermal spray technique, especially WC spray powder,  there are more and more china spray powder suppliers and manufacturers, accelerating the development of thermal spraying technique.

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Something you should know about thermal barrier coatings

Thermal barrier coating is mostly studied in thermal spraying technique, and it’s one of the most important coatings which with most development potential.

Usually, thermal barrier coating works in a high temperature9(above 1000℃）)environment, the thermal barrier coating is a "Laminated" type, metal and ceramic composite coating

Which is composed of metal buffer layer and thermal protection ceramic functional coating which with good heat resistance and thermal insulation. Work coating of surface ceramics are combined with high temperature alloy substrate recur to the metal bonding layer between substrate and ceramic coating.

The bonding layer has good adhesion with surface ceramic layer and basis metallic material, and with excellent high temperature resistance and oxidation resistance, thermal expansion coefficient between base metal and surface ceramic layer, it can improve heat matching between ceramic and metal materials, reducing interfacial stress, and improving the boding strength, thermal shock resistance and operating life.

Preparation of thermal barrier coating is usually sprayed with plasma spraying process, HVOF flame spray coating technology is more suitable for functionally Graded thermal barrier coatings. YSZ is the most practical ceramic materials for preparation of thermal barrier coatings, usually, bonding materials are alloy materials of MCrAIY.  Based on some correlational studies, except the choosing of materials, the structure design of coating is also an important factor which affects practical performance of thermal barrier coating. 

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Property Inspection Methods of corrosion-resistant coating

Corrosion is a process of material (especially the metal material) damaging or performance deterioration which issues chemical, electrochemical reaction or physical dissolve in the ambient medium. Corrosion-resistance coating is born to withstand the phenomenon, laboratory experiment and field coupon test are two methods to inspect property of materials’ corrosion resistance.

1. There are many laboratory experiment test methods for thermal spray coating corrosion testing, such as outdoor exposure test, Liquefied dipping experiment, salt spray test, Damp and hot corrosion test, Sulphur dioxide industrial atmosphere corrosion test, Hot corrosion experiment, electrochemical testing. Field coupon test is aiming at working environment of the workpiece, choosing environmental medium and the same conditions of field, such as atmosphere, seawater, fresh water, soil. All kinds of chemical mediums and additional piece going along with the equipment operation to identify its corrosion resistance. It takes a long time to get the conclusion by the data of field coupon testing, but through intensive laboratory experiment, we can know coating working environment and simulating the coating corrosion resistance in its actual use in a short time. So laboratory corrosion testing is the better choice for production testing.

（2）Field coupon and simulation are usually on the basis of laboratory experiments, it’s a further testing for actual corrosion of material. The evaluation of corrosion test results, result of macroscopic and microscopic observation is considered. The uniform corrosion is mainly measured by corrosion rate, the corrosion rate is the loss of material in unit time and on unit area.
To my knowledge, Agglomerated and Sintered WC Co Tungsten Carbide Thermal Spray Powder is the best corrosion-resistant spray powder.

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