超音速火焰喷涂WC-Co层的高温氧化对摩擦磨损性能的影响
The Effect of Oxidation at Elevated Temperature on Tribological Behavior of WC-Co HVOF Spraying Coatings
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摘要: 针对WC-12Co和WC-17Co超音速火焰喷涂层(HVOF),采用球/盘试验机研究其在大气环境下从室温至800℃的摩擦磨损性能,并结合涂层的氧化试验、氧化产物的XRD和Raman光谱分析、磨痕表面SEM观测,探索高温氧化对涂层摩擦磨损机制的影响.结果表明:WC-Co涂层在350~450℃时的摩擦磨损主要受Co氧化物的控制,体积流失小,为轻微氧化磨损;高于500℃时,WO3增多,虽有利于减摩却因消耗WC使涂层耐磨损性能下降;摩擦作用促进CoWO4的形成,这种钨钴双氧化物能够降低摩擦,减轻磨损,使涂层在600℃高温下仍维持良好的摩擦学性能;在更高温度条件下氧化剧烈,涂层性能迅速恶化而发生严重磨损,不宜作为耐磨涂层使用.Co含量较高的WC-Co涂层具有更好的高温耐磨性.Abstract: Friction and wear performance of WC-12Co and WC-17Co HVOF spraying coatings within the temperature range of 25~800℃ in atmospheric environment was studied by a ball-on-disc tribometer. The worn track morphologies, phases of products after rubbing tests were measured by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Combining with the oxidation tests of coatings the effect of oxidation at elevated temperature on the tribological behaviors was investigated. The results show that at 350 and 450℃, the wear of coatings was influenced by cobalt oxides and revealed the mild oxidative wear. At 500℃, WO3 increased with the depletion of WC hard phase, which was beneficial to the antifriction properties and unbeneficial to the wear resistance. The friction behavior could promote CoWO4 formation. Cobalt tungstate was able to reduce the friction and wear and enabled the coating to maintain good tribological properties even at 600℃. Above 600℃, the coatings oxidized seriously and their properties deteriorated rapidly, which caused serious wear. Thus WC-Co coatings should not be used as wear-resistant coatings above 600℃. The coating with higher cobalt content demonstrated better high temperature wear resistance.