Abstract
This paper presents new results of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM) investigation of the structure-phase compositions of coatings on the base of Ni and Co deposited by plasma-detonation on steel substrates after their modification by DC plasma jet irradiation. The phase structures and morphology of precipitation of strengthening phases from solid solution are defined. The irradiation of the coatings leads to the evolution of the structural-phase state of coatings: an increase in the size of the diffusion zone between the coating and the substrate, an increase in the volume fraction of hardening intermetallic phases, the formation of sufficiently homogeneous fine-grained structure in the irradiated coatings and, consequently, a significant increase of hardness, corrosion and wear resistance of modified coatings. There is a mutual penetration of the substrate main element Fe in the coating and base coating elements (Ni and Co correspondingly) into the substrate as a result of the coating treatment by a pulse DC plasma jet. DOI: http://dx.doi.org/10.5755/j01.ms.22.2.7699
Highlights
The protective powder Ni and Co based coatings produced by the methods of Thermal Coating Spraying, High Velocity Oxy-Fuel (HVOF) coating spraying or plasma detonation designed for the protection of surfaces of industrial products working at high temperatures and in corrosive environments [1 – 7]
We have carried out model calculations of temperature distribution in the two-layer absorbers heated by a moving source; on their basis were given recommendations on exposure modes, presumably to ensure certain temperature profiles, acceleration of diffusion processes and the precipitation of certain phases
We suggested development of radiation-enhanced diffusion in the absorbing materials during irradiation; but without experimental measurement of diffusion coefficients we are unable to predetermine the contribution of one or another factor in the acceleration of mass transfer, except that by circumstantial evidence
Summary
The protective powder Ni and Co based coatings produced by the methods of Thermal Coating Spraying, High Velocity Oxy-Fuel (HVOF) coating spraying or plasma detonation designed for the protection of surfaces of industrial products working at high temperatures and in corrosive environments (cylinder liners, cervical shaft gas turbine engine compressor stators, the details of construction of pipelines, etc) [1 – 7]. The plasma detonated Ni and Co-based coatings have an fcc lattice [14 – 17], which provides some technological advantages. The alloys with the fcc lattice have higher welding properties and better endurance capability at high temperatures. Their grains are unlikely to increase during heating, and retain ductility at low temperatures [12]. We have carried out model calculations of temperature distribution in the two-layer absorbers heated by a moving source; on their basis were given recommendations on exposure modes, presumably to ensure certain temperature profiles, acceleration of diffusion processes and the precipitation of certain phases in the protective powder coatings deposited by a plasma jet on steel substrate [14, 17]
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