Plasma Spraying, The Preparation Of Nanometer Cr < Sub > 2 < / Sub > O < Sub > 3 < / Sub > Coating Research

The hardness and wear resistance of nano-sized chrome oxide （Cr₂O₃） coating are superiorto those of micro-sized Cr₂O₃coating. Aimed to the preparation nano-sized Cr₂O₃coating, thestudy on a complete process has been developed on the basis of the summarized researchprogress of plasma spray micro-sized Cr₂O₃coating and nano-sized Cr₂O₃coating. In thecomplete process, nano-sized spherical Cr₂O₃powder was firstly prepared and the agglomeratedpowder of nano-sized Cr₂O₃was then achieved by spray prilling and sintering and nano-sizedCr₂O₃coating is fabricated by air plasma spray （APS） eventually. The performance of the coatingwas further studied.The main subjects in this dissertation are as follows:（1） Low-temperature hydrogen-reduction sintering method and milling technique werecombined to prepare the nano-sized spherical Cr₂O₃powder. Orthogonal experiments wereconducted to explore the effect of the weight ratio of ball to powder, the milling speed and themilling time on the size and morphology of Cr₂O₃powder. The milling technique was alsooptimized. The particle size of the spherical Cr₂O₃powder products of good crystallization isbetween60nm and120nm and the apparent density is determined as about1.21g/cm³.（2） The spray dring technique and activated sintering method were used to prepare theagglomerated powder of nano-sized Cr₂O₃, because the nano-sized Cr₂O₃powder is unsuitable fordirect APS. The spray dring technique was further optimized on the basis of the study of solidcontent of slurry, binder, water reducer and the working parameters of spary dryer, such as airtemperature, blower rate and feed rate on the morphology of the agglomerated nano-sized Cr₂O₃powder.The size of the agglomerated powder is about50μm. The apparent density and thevibration density are determined as1.67g/cm³and2.37g/cm³respectively and the liquidity isalso achieved as48.5s/50g. The agglomerated nano-sized Cr₂O₃powder product is provedsuitable for APS.（3） Orthogonal experiments were conducted to study the effect of air plasma sprayingparameters, such as plasma current, Ar gas flow rate, electric voltage and spray distance on theVickers microhardness and the tribological behaviours. The wear mechanisms of nano-sizedCr₂O₃coating were further studied.