It was known for long that Ni-Al composite powders can be used to deposit self-bonding coating as a bond coat for common ceramic coatings due to the exothermic reaction between Ni and Al. However, it was found that with commercial Ni-Al composite powders with a large particle size, it is difficult to ignite the self-propagating reaction between Ni and Al to form Ni-Al intermetallics by plasma spraying. In this study, Ni-Al composite powder particles of different sizes were used to prepare Ni-Al intermetallics-based coatings by plasma spraying. The dependencies of the exothermic reaction between Ni and Al and the coating microstructure on powder particle size and spray parameters were investigated. The phase composition, microstructure, porosity and oxide content of the coatings were characterized by x-ray diffraction, scanning electron microscope and image analyzing. The results show that particle size of Ni-Al composite powders is the dominant factor controlling the exothermic reaction for the formation of Ni-Al intermetallics during plasma spraying. When the powders larger than about 50 μm are used, the reaction forming aluminide cannot complete even by heating of plasma flame generated at high plasma arc power. However, when smaller powders less than 50 μm are used, the exothermic reaction can completely occur rapidly in plasma spraying, contributing to heating of Ni-Al droplets to the highest temperature for development of the self-bonding effect. The positive relationship between molten droplet temperature and tensile adhesive strength of the resultant coatings is recognized to confirm the contribution of high droplet temperature to the adhesive or cohesive strength.

中文翻译：

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粉末粒径和喷涂参数对 Ni-Al 复合粉末等离子喷涂过程中 Ni/Al 反应的影响

由于Ni和Al之间的放热反应，人们早就知道Ni-Al复合粉末可用于沉积自粘合涂层作为普通陶瓷涂层的粘合涂层。然而，研究发现，商业化的大粒径Ni-Al复合粉末难以通过等离子喷涂点燃Ni和Al之间的自蔓延反应形成Ni-Al金属间化合物。在本研究中，采用不同尺寸的 Ni-Al 复合粉末颗粒通过等离子喷涂制备 Ni-Al 金属间化合物基涂层。研究了 Ni 和 Al 之间的放热反应和涂层微观结构对粉末粒度和喷涂参数的依赖性。通过X射线衍射表征涂层的相组成、微观结构、孔隙率和氧化物含量，扫描电子显微镜和图像分析。结果表明，Ni-Al复合粉末的粒径是控制等离子喷涂过程中形成Ni-Al金属间化合物的放热反应的主导因素。当使用大于约50μm的粉末时，即使加热以高等离子弧功率产生的等离子火焰，形成铝化物的反应也不能完成。然而，当使用小于 50 μm 的较小粉末时，等离子喷涂中的放热反应可以完全快速发生，有助于将 Ni-Al 液滴加热到最高温度以发展自结合效应。