Suspension chemistry and electrophoretic deposition of YSZ-NiO nano-composite films on an iron-nickel based superalloy

Abstract

Suspensions of mixed YSZ (3 mol%) and Ni particles in acetylacetone medium were prepared using iodine as a dispersant. The effect of iodine concentration on suspension stability, particle size distribution and zeta potential of suspensions were studied to optimize the suspension chemistry. Electrophoretic deposition (EPD) method was applied for the preparation of green form YSZ/Ni nano-composite coating with suspension of YSZ and Ni particles in acetylacetone in presence of 0.2 g/l iodine. Based on the derived results, both applied voltage of 7 V and deposition time of 4 min are suitable for deposition of green composite coating. After deposition, green form coatings were heat treated at 500 °C for 1 h for oxidation of nickel particles and further sintered at 1100 °C for 4 h in the air. For the first time, the reaction bonding process along with the sintering heat treatment were studied and developed to fabricate uniform, crack-free and dense YSZ/NiO coatings. The volume shrinkage of the coating was compensated by the volume expansion, caused by oxidation of nickel in the green coatings. Also, addition of Ni particles to YSZ lowered the sintering temperature of the coating about 300 °C, since sintering temperature of the pure YSZ is 1400 °C but after addition of nickel the coating was sintered at 1100 °C. The coating adhesion to substrate was evaluated using ASTM D3359 and Rockwell C indentation (VDI 3398) methods. The result of adhesion tests showed that the coatings have good adhesion strength (5B according to ASTM D3359B).

Graphical Abstract

Keywords:

• Nano YSZ/NiO
• composite coating
• electrophoretic deposition
• suspension
• reaction bonding