Tham khảo tài liệu 'advances in gas turbine technology part 18', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 500 Advances in Gas Turbine Technology substrate. As the process continues particles continue to impact the substrate and form bonds with the deposited particles resulting in a uniform coating with very less pores and high bond strength. The term cold spray has been used to describe this process due to the relatively low temperatures of the expanded gas stream that exits the nozzle. Cold spray as a coating technique was initially developed in the mid-1980s at the Institute for Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Science in Novosibirsk. The Russian scientists successfully deposited a wide range of pure metals metallic alloys and composites onto a variety of substrate materials and they demonstrated that very high coating deposition rates are attainable using the cold spray process. Fig. 1. Schematic illustration of cold spray apparatus The temperature of the gas stream is always below the melting point of the particulate material during cold spray and the resultant coating and or freestanding structure is formed in the solid state. Since adhesion of the metal powder to the substrate as well as the cohesion of the deposited material is accomplished in the solid state the characteristics of the cold spray deposit are quite unique. Because particle oxidation is avoided cold spray produces coatings that are more durable with better bonding. One of the most deleterious effects of depositing coatings at high temperatures is the residual stress that develops especially at the substrate-coating interface. These stresses often cause debonding. This problem is compounded when the substrate material is different from the coating material. This problem is minimized when cold spray is used. In addition interfacial instability due to differing viscosities and the resulting roll-ups and vortices promote interfacial bonding by increasing the interfacial area giving rise to material mixing at the interface and providing mechanical .
