Effects of spraying parameters onto flame-sprayed glaze coating structures

Thanks to their design characteristics (i.e., colors, brightness, opacity, etc.) and/or physical properties (i.e., durability, low thermal conductivity, tightness, etc.), glazes find numerous applications, from art ornamenting to protection against corrosion. Glazing consists in coating a substrate by fusing various mineral substances over it. This is a low cost process and hence can be applied on large surfaces. Conventional glazing process needs a relatively high temperature treatment (i.e., up to 1400 °C) that heat-sensitive substrates do not sustain.Thermal spraying may be a good solution to prevent the substrate from thermal degradation. Flame spraying was considered as the spray technique due to its low operating cost and the possibility to adapt the glaze transition temperature to the operating parameters.When spraying glazes, the coating formation mechanism is different from the one encountered with crystallized ceramic materials. Indeed, the high surface tension of those feedstock prevents the particles from being totally spread (i.e., “dewetting” phenomena). Here, the coating results from the coalescence of impinging particles to form a monolayer.The effects of glaze morphology on coatings were studied in this paper. Chemical analysis also permitted to determine the influence of spray parameters on glaze compositions, that can affect glazes thermal properties and hence modify coating structures. At last, the effects of operating parameters on coating architecture were analyzed by experimental design.     

前驱体溶液等离子喷涂参数对涂层形貌的影响及沉积行为机理研究

目的对不同喷涂工艺参数下涂层的相结构、显微形貌进行研究,确定优化的喷涂工艺参数,讨论分析涂层的沉积行为机理。方法采用前驱体溶液等离子喷涂(SPPS)的方法制备纳米Yb_2O_3稳定的ZrO_2(YbSZ)涂层。在传统等离子喷涂的基础上,增加液料雾化装置,雾化喷嘴将溶液雾化后直接注入到等离子弧中,通过控制喷涂距离及喷涂功率,研究了涂层相结构、结晶度、晶粒尺寸以及显微形貌的变化趋势,并且结合显微形貌讨论了沉积机理。结果涂层呈现团聚大颗粒、纳米级粒子、大小均匀的孔隙三种显微形貌,大颗粒之间呈堆积形态。当喷涂功率为30 kW时,涂层呈现m-ZrO_2,平均晶粒尺寸达669 nm。随着喷涂距离、喷涂功率的增加,样品中检测到单一的t-ZrO_2相,而且纳米尺寸颗粒的数量大大增加,孔径变小。随着喷涂距离由60 mm增加到100 mm,平均晶粒尺寸先由429 nm减小到177 nm,随后又增加到319 nm。结论喷涂参数影响晶粒的结晶度、晶粒尺寸以及涂层的显微形貌,低功率下得到的涂层存在糊状未结晶组织。增大喷涂功率,可以有效增大结晶度和晶粒尺寸;随着喷涂距离的增大,晶粒尺寸先减小后增大。雾化液滴在等离子火焰中一般要经历浓缩、饱和、固化、析晶形核长大、粒子重熔扁平化的历程,喷涂功率越高,经历温区越高,液滴演变就越充分,通过优化工艺参数可以得到不同结构性能的功能涂层。