Novel Strategy for Developing Bulk-like dense Oxide-free Metallic Coatings by Atmospheric Plasma Spraying

Although thermal spray metallic coatings have been widely used for materials protection from wear, corrosion and oxidation, its porous feature limits the full utilization of materials potential. Moreover, the oxidation inherent to thermal spraying in ambient atmosphere is detrimental to interlamellar bonding formation which further reduces coating performance. Facing such challenge, the novel strategy to deposit oxide-free dense metallic coatings by atmospheric plasma spraying has been developing. The strategy includes development of the ultra-high temperature metallic droplets up to 2650^oC with the in-situ deoxide effect achieved by material design with deoxiding element in the powder. The evaporation or gasification of the resultant oxides at high temperature generates the in-situ deoxiding effect during in-flight. Moreover, the subequent impact of ultra-high temperature droplets creates a self-metallurgical bonding effect. Thus, fully dense bulk-like metallic coatings can be formed by APS. In this report, the typical examples of NiCrMo coatings, NiCrBSi coatings, NiAl coatings will be presented to show clearly the possibility to deposit oxide-free metal coatings with sufficiently bonded lamellae by APS following the above strategy. Such strategy will tape out the full potential of coating materials and open up the new application fields for plasma spraying.