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

如果对多组分复合粉末进行喷涂，人们担心在喷涂过程中会出现热不稳定物质的分解。然而，反应喷涂对于形成原位复合涂层是非常有效的，因为所需的和热力学稳定的化合物可以通过过程反应合成。研究结果如下：(1)采用直流等离子喷涂技术制备了含石墨固体润滑剂的铸铁涂层，用于铝基体的表面改性。特别设计的铸铁粉，由高硅和强石墨化剂铝合金化而成，作为喷涂材料。为了形成具有石墨结构的铸铁涂层，(a)对铸铁粉末进行预退火，(b)对喷涂涂层进行后退火，(c)添加固体润滑剂hBN。石墨结构铸铁涂层表现出情绪摩擦学性能。(2)对Al-40wt%Si-10wt%Mg合金粉末进行直流、射频等离子喷涂和HVOF喷涂。HVOF喷涂由于精细的微观组织和加工硬化而具有最高的硬度。在射频等离子体喷涂过程中，镁的蒸发导致Mg_2Si的增强相减少。期望在Al-Si - Mg粉末与SiO_2混合的情况下，通过SiO_2的还原反应可以得到原位复合涂层。直流等离子喷涂涂层硬度最高，工艺反应进行程度高，这是由于最佳熔滴温度导致MgAl_2O_4含量高。

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.