Microstructures And High Temperature Erosion Properties Of Supersonic Arc-sprayed Composite Coatings Of Cored Wires Containing Intermetallics And Nanosized Ceramics Under Nitrogen Protective Atmosphere

Supersonic arc spray technology was used as the most practicable method and manufacturing equipment of spraying material, arc spray machine, spraying technique, arc spray materials and testing apparatus for the coatings were investigated comprehensively, thoroughly and innovatively in this paper proceed form feasibility of investigation method and application value of investigation achievement, according to actual problem that there were serious high temperature erosion phenomenon and enormous economical losses caused on the boiler tubes of coal-fired power plants at home and abroad. The advantages of arc spray technology were developed and its' defects were overcome in the investigation. The arc spray technology, equipment, technique, spraying materials and coatings' properties were developed to a completely new level after the research, and then there are very good actual use value and important scientific significance. Quite good applied effect and economic benefit are proved after on-the-spot application.The special equipments for manufacturing arc spray cored wire: drawing-rolling style overlapping cored wire covering machine (CWCM05) and tension style cored wire drawing machine CWDM05) were investigated, designed and manufactured for the first time. Successful manufacture of the equipments provided basic guarantee for the doctor project. They can be used not only for investigation of coatings' composition, spray technology, structure and properties, but also for development of much new kinds of spraying materials and new arc spray coatings. The cored wires manufactured by CWCM05 and CWDM05 have good apparent mass, fineness, smooth, roundness, overlapping and powder cored consistency. Test by arc spraying performed that the cored wire went smoothly, arc sprayed stably and there was no detonation phenomenon. The special equipments can manufacture cored wires 500 tons per year approximately. We have gained invention patent right (Invention patent number: ZL200410017882.9).N₂ protective atmosphere was put forward for controlling oxidation of arc-sprayed materials, and then N₂ protective device used for supersonic arc spray wason microstructure, porosity, inter-diffusion of interface, hardness, bond strength, cohesive force, oxidation resistance and high temperature erosion resistance was investigated by using the cored wire containing composite cored powder (56%Cr₃C₂+30%Cr+6%V-Fe+4%Nb-Fe+4%Mn) as the coating material. Effect of N₂ protection was also investigated by testing comparison. At last, the best technological parameters of arc spray that was feasible for application was selected for following investigations of spraying materials. We have also applied for patent.Microstructures and high temperature erosion of arc spray coatings of Ti-Al intermetallics composite materials were investigated by using the feature of cored wire for the first time. High temperature erosion resistance of the coatings of developed cored wires decreased in the order of ACW1>ACW4≥ACW2>ACW3. By optimization of spraying process factors, Ti-Al intermetallics composite materials will be able to use as excellent coating material of anti-high temperature erosion. The arc spraying coatings exhibited typical "lamination" microstructure. The oxides located between "splat" were caused by oxidation of both the cored powders and the iron sheaths. Erosion mechanisms of the spraying coatings under the present testing conditions included brittle breaking, fatigue spalling, cutting and ploughing.Supercritical erosion regularity of arc spraying coatings of Ti-Al and Cr intermetallics composite materials was investigated. The "lamination" microstructure feature that solid solutions were laminated by oxides in the coatings of BCW1 and BCW2 was discovered. Oxide existed in the form of Fe₃O₄. The result of 800℃ , 150h oxidation testing shows that oxidation resistances of BCW1and BCW2 coatings were 10 and 15 times of that of 20 carbon steel respectively. The highest erosive rate of 20 carbon steel occurred near 15 degree, but that of BCW1 and BCW2 coatings appeared near 45 degree. Whether or not impinging angle was high (or low), erosion resistance of BCW1 and BCW2 coatings was obviously higher than that of 20 carbon steel. Erosion resistances of BCW1 and BCW2 coatings were 3.1 and 3.0 times of that of 20 carbon steel respectively.Influence of N₂ protective atmosphere on microstructures and high temperature erosion of TiAl₃ and Cr₃C₂ composite material coatings by supersonic arc spray wasinvestigated. It was discovered that the coating arc-sprayed under N₂ protective atmosphere had denser and more homogeneous structure, fewer oxide inclusion and higher hardness than under air atmosphere. In this testing condition, separation between splats and fracture, surging and spalling of splat was the main reason of erosion wear. Oxide inclusions reduced obviously cohesive force between splats, therefore decreased high temperature erosion resistance of the coating. The volume erosive rates of CCW1, CCW2 and CCW3 coatings arc-sprayed under N₂ protective atmosphere decreased by 3.3, 2.3 and 1.0 times as that under air atmosphere.Influence of age on microstructures and high temperature erosion of composite material coatings containing nanosized ceramics by supersonic arc spray was investigated. The cored powders and the iron sheaths could form homogeneous solid solution by fusing and mixing in the process of arc spraying composite materials containing nanosized ceramics. It was discovered that age reduced defects of crystal lattice, removed concentrated stress, increased crystallization content, decreased hole and cavity, resolved instable phase, thus raised fairly hardness of the coating and made hardness distribute more homogeneously. Age did not increase high temperature erosion resistance of DCW3 coating, but increased that of DCW1 and DCW2 coatings by 20% and 29% respectively.Influence of N₂ protective atmosphere on microstructures and high temperature erosion of composite material coatings containing nanosized ceramics by supersonic arc spray was investigated for the first time. N₂ protective atmosphere could raise density and homogeny of coatings, improve continuity and reduce oxides of coatings very much. N₂ protective atmosphere also made more alloy elements fuse and mix into iron to form iron-based solid solution. Analysis by TEM (transmission electron microscope) shows that nanosized ceramics phase was distributed in the based solution in a form of dispersion. Oxides in the coatings were one of main facts that affected erosion resistance. The coatings sprayed nuder N₂ protective atmosphere did not occur obviously in the form of lamination of material loss when eroded by erosive abrasives, so the erosive rates were quite low. The volume erosive rates of ECW1, ECW2 and ECW3 coatings arc-sprayed under N₂ protective atmosphere decreased by3.4, 6.4 and 6.5 times as that under air atmosphere. N₂ protective atmosphere reduced burning loss of nanosized ceramics very much, improved bonding of nanosized ceramics phase and base phase, and gave full play of nanosized ceramics to disperse hardening effect. We have gained invention patent right (Invention patent number: ZL200410017882.9).