Study on Unified Understanding of Fundamental Coating Steps in Reactive Thermal Sprayings

如果喷涂由多组分组成的复合粉末，则担心在其喷涂过程中会发生热不稳定物种的分解。然而，反应喷涂是相当有效的形成原位复合涂层，因为所需的和热稳定的化合物可以通过过程中的反应合成。研究结果如下：（1）采用直流等离子喷涂技术在铝基体表面制备了石墨固体润滑铸铁涂层。采用特殊设计的铸铁粉，加入高硅、强石墨化剂铝合金，作为喷涂材料。为了形成具有石墨结构的铸铁涂层，（a）铸铁粉末的预退火，（B）喷涂涂层的后退火和（c）与另外的hBN固体润滑剂混合。石墨结构的铸铁涂层具有良好的摩擦学性能。(2)采用直流、射频等离子喷涂和超音速火焰喷涂方法制备了Al-40wt%Si-10wt%Mg合金粉末。HVOF喷涂由于组织细化和加工硬化而具有最高的硬度。镁在射频等离子喷涂过程中发生蒸发，导致Mg_2Si增强相减少。在Al-Si Mg粉中加入SiO_2，可望通过SiO_2的还原反应获得原位复合涂层。直流等离子喷涂的涂层硬度最高，这是由于直流等离子喷涂的最佳熔滴温度导致了较高的MgAl_2O_4含量，从而使工艺反应高度进行。

If composite powders consisted of multi-constituents are sprayed, it is worried about the decomposition of thermodynamically unstable species may occur in their spraying process. However, reactive spraying is quite effective to form in-situ composite coatings, because the required and thermodynamically stable compounds can be synthesized by the in process reaction. Following results are obtained in this study :(1) Cast iron coatings with solid lubricant of graphite were formed by DC plasma spraying for the surface modification of aluminum substrates. Specially designed cast iron powder, which were alloyed with high silicon and aluminum of strong graphitizer, were supplied as a spray material. In order to form cast iron coatings with graphite structure, (a) pre-annealing of cast iron powder, (b) post annealing of sprayed coatings and (c) mixing with additional solid lubricant of hBN. The cast iron coatings with graphite structure exhibits mood tribological properties.(2) Alloyed powder of Al-40wt%Si-10wt%Mg were sprayed by DC and RF plasma spraying, and also HVOF spraying. HVOF spraying gives the highest hardness among them due to refined microstructure and work hardening. The evaporation of magnesium occurs during the RF plasma spraying process, which causes less reinforced phase of Mg_2Si. It is expected that the in process reaction of SiO_2 reduction give us in situ composite coating in the case of Al-Si Mg powder mixed with SiO_2. The coatings with DC plasma spraying show the highest hardness, that is, the highly proceeded in process reaction, because it causes the high amount of MgAl_2O_4 due to the optimum droplet temperature.