Papers by Keyword: Plasma Spraying

Abstract: The plasma spraying is commonly used in medical application. The Atmospheric Plasma Spray (APS) method was applied for production of yttria-stabilized zirconia (YSZ) on AISI 316L stainless steel surface and also on Ti6Al4V titanium alloy surface. In present article two examples of coatings production were presented. In first experimental the YSZ was plasma sprayed (APS) on 316L stainless steel surface. The coating was deposited using A60 (Thermico) plasma torch. The initial parameters were selected and it was concluded that minimal power current was 500A. The thickness of obtained coating was in range 100-150 micrometers. The X-ray phase analysis showed the presence of tetragonal t-phase of ZrO₂. The lamellar structure of coatings with large porosity was observed. In second experimental the newly developed Plasma Spray Physical Vapor Deposition method (PS-PVD) was used. The YSZ coating was deposited on titanium Grade 5 surface. The conducted research showed the formation of two types of coatings structure. When the power current was lower (2000 A) the dense lamellar-like coatings was obtained. If the power current was increased (up to 2200A) the columnar ceramic coating was observed.

Abstract: Compared with the atmosphere plasma spraying (APS), low pressure plasma spraying (LPPS) has been widely used due to deposit a specific and unique coating. A new low pressure thermal spraying plasma torch was designed according to the plasma spray characteristic in the low pressure environment. The plasma jet characteristic and the coatings microstructure were analyzed. In this study, Kundsen number has a great effect on the heat transfer of feedstock powder. With the increase of current, the plasma torch efficiency will decrease. A equiaxed microstructure of 316L coatings were deposited.

Abstract: The method to determine thermal fields considering dependence of thermophysical and mechanical properties of coating materials and a base from the temperature, the running of plastic deformations and stresses relaxation at plasma spraying is suggested. The mathematical model of calculation of thermal field with moving boundary considering nonlinear feature of coating growth at layer-by-layer deposition and dependences from thermophysical properties of materials of the system «coating-base» is developed. The model application helps to estimate the effect of the parameters of plasma spraying process on the level of the residual stresses in the increased coatings.

Abstract: The article considers issues related to the choice of abrasive material and technology of its use for the formation of necessary roughness on the base material and necessary heat resistance of the heat-protective coating during plasma spraying. The influence of the shape and size of the abrasive on final roughness of the treated surface was studied at various angles of contact between the sprayed abrasive and the surface (angle of attack). From the condition of maximum heat resistance, the composition of the heat-resistant composite coating of the spinel type was determined, which consists of 3 layers: the 1st layer (sublayer) material is a chromium-aluminum composite and the 2nd layer of a transitional spinel-based aluminum and chromium oxide + chromium-aluminum composite and the 3rd a layer of spinel based on aluminum and chromium oxides.

Abstract: Due to the increasing of the price of different materials and resource saving it is very promising to develop technology of creation cheap coatings with specified properties. We developed a diffusion-doped powder based on austenitic steels for producing plasma-sprayed coatings. In comparison with Ni-based powders our materials have better adhesion, they are cheaper, they have better mechanical machinability, it is possible to produce coatings with required properties. In our work, the features of diffusion doping of microparticles of powder, the behavior of the powder in the plasma jet were studied. The significant decreasing of porosity, increasing of adhesion of the plasma-sprayed coatings after laser processing were marked. The substantial increase of wear-resistance in 2,5-3,0 times in comparison with untreated coatings when working in conditions of abrasive wear and atmospheric precipitation was revealed.

Abstract: Conventional and nanometer aggregate ZrO₂-7wt.%Y₂O₃ ceramic powders taken as raw materials, plasma spraying and plasma spraying-laser remelting compound technology was used to prepare conventional and nanostructured thermal barrier coatings on the TiAl alloy surface. Effects of powder structure (feedstock) and laser remelting on organizational structure and phase of the coatings were analyzed using scanning electron microscope (SEM) and X-ray diffractometer (XRD). Results indicate that: conventional plasma sprayed ceramic coating presents typical lamellar stacking features; plasma sprayed nanostructured coating consists of fully melted region and partially melted region, presenting a two-phase structure. Under the comprehensive impacts of laser power, energy density, temperature field distribution in the laser action region, ceramic heat conductivity coefficient and coating thickness and other factors, the coating presents obvious lamellar structural features after laser remelting; the upper part is compact columnar crystal remelting region and the lower part is residual plasma spraying region. Due to toughening effect of residual nanoparticles in the remelting region of laser remelted nanostructured coating, grain-boundary strength is high and there are a considerable number of transgranular fractures, but the fractures in the remelting region of laser remelted conventional coating are basically intergranular fractures. Conventional plasma sprayed ceramic coating is mainly of tetragonal phase together with a small quantity of monoclinic phases, but nanometer plasma sprayed ceramic coating only has non-equilibrium tetragonal phases. After laser remelting, both conventional coating and nanometer coating mainly have non-equilibrium tetragonal phases with a small quantity of cubic phases.

Abstract: This article is dedicated to the questions of development of technological bases for the manufacturing blanks of friction disks with molybdenum gas-thermal coating applied by plasma spraying, for working in oil in the transmission units of transport machines. For ensure high performance indicators, there is has been offered a technological scheme for manufacturing friction disk blanks: short blasting preparation of the surface of the disk’s steel base, applying a molybdenum coating, that characterized by high adhesion to the ferrous metals, mechanical processing of the coating by grinding, monitoring the coating’s quality. The developed technological bases for manufacturing blanks of friction disks with molybdenum gas-thermal coating, applied by plasma spraying, for working in oil in transmission units of transport machines are contributed to the creation of efficient products with enhanced performance indicators for friction coefficient, wear resistance, reliability in modern conditions at the enterprises.

Abstract: Plasma spraying technique was used to prepare MCrAlY coating on TiAl alloy surface, the coating was treated through the laser remelting process, and then scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to analyze surface topography and phase composition before and after hot corrosion behavior of the coating. Results indicate that after laser remelting treatment, lamellar structure of the coating disappears with improved compactness and most defects like pores and inclusion eliminated. Plasma sprayed MCrAlY coating can significantly improve hot corrosion property of TiAl alloy, which can be further improved after laser remelting. MCrAlY coating mainly experiences surface oxidation reaction and internal sulfurization reaction during the hot corrosion in the high-temperature molten salt, which mainly generate corrosion products such as Al₂O₃, Cr₂O₃, NiO, NiCr₂O₄, Ni₃S₂ and CrS.

Abstract: In this study, the influence of plasma and detonation spraying techniques on the microstructure and wear behaviour of FeNiCrBSiC-20wt%CrB₂ coating was investigated. The obtained coatings were found to comprise of Fe, Ni-based solid solution matrix reinforced with mixed boride phases (Fe,Cr)₂B, (Ni,Fe,Cr)B, (Cr,Fe,Ni, Mo)B. The main microstructural differences of the plasma and detonation sprayed coatings are the morphology, the size and the distribution of hard boride particles. The tribological behaviour of coatings was examined under dry sliding conditions against Al₂O₃ ball at 20, 200 and 400 °C. The wear loss of detonation sprayed coatings was slightly lower at high temperatures while plasma sprayed coating had same wear at all temperatures. The investigation of worn surfaces revealed that abrasive and oxidative wear mechanisms are proved to be dominant for FeNiCrBSiC−20wt.%CrB₂ plasma sprayed coatings, while brittle delamination and oxidative wear are characteristic for detonation sprayed coating. The sliding wear loss of the unreinforced commercial FeNiCrBSiC plasma sprayed coating was 2-3 times higher than that of reinforced (with chromium boride) coating at high temperatures due to splat delamination.

Abstract: The thermal barrier coating samples of different thickness with alumina coated zirconia and zirconia as coating materials were prepared on the surface of heat resistant alloy steel substrate after activation treatment with NiCoCrAlY as adhesive transition layer by plasma spraying method and spray gun quick spraying process. The bonding strength and thermal insulation property of two kinds of ceramic coating with the same thickness were compared by the test results of bonding strength, high temperature heat insulation and microstructure, and the relationship between the coating thickness and heat insulation effect were investigated. The results indicate that the structure and property of thermal barrier coating using nanoAl₂O₃ coated ZrO₂-Y₂O₃ powder are superior to that using single zirconia powder. The thermal insulation property of the thermal barrier coating increased with the increasing of coating thickness, and the advantage is more obvious with temperature increasing.