Hybrid Spraying of Zirconia Thermal Barrier Coating with YAG Laser Combined Plasma Beam
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As an ideal zirconia thermal barrier coating, a microstructure with strong bonding among coating particles and with a certain amount of porosity in the coating, but without connected porosity, is desirable. However, it is difficult for normal plasma-spraying to create a zirconia coating with these characteristics. In order to obtain these characteristics, we prepared zirconia coatings on steel substrates under coated with NiCrAlY alloys, by means of a hybrid spraying (that is, YAG laser combined with plasma spraying) and studied the effect of this hybrid spraying process and plasma and laser conditions on the microstructure of the coating, and further compared the microstructure of the coating from this hybrid spraying with that in post-laser irradiation of as-sprayed zirconia coatings. It is known that microstructures with densification are formed by the post-laser irradiation of as-sprayed coatings and that microcracks are produced in the process of rapid cooling. However, by using this newly-developed hybrid spraying, the microstructure with partial densification in the coating and without connected porosity was formed and cracks which are generally produced in the post-laser irradiation treatment were inhibited completely. In addition, this hybrid spraying can be done without the post-treatment of coating. Furthermore, the coating properties, such as hardness and wear resistance arising from the bonding state among the coating particles in the zirconia coating created by this hybrid spraying were improved.
- Trans. JWRI
Trans. JWRI 26(1), 99-107, 1997