Evaluation of Microstructure, Phase Composition and Properties of Four Layer Zirconia Coating on API5L Steel as a Function of Different Sintering Condition

In this study four layers of zirconia coating were applied on the surface of API5L steel samples by sol-gel method using zirconium isopropoxide precursor. In the first group of samples, after each layer of coating and for the second group after four-layer coating, heat treatment (calcination and sintering) were carried out at the desired temperatures (350-550 C). X-ray diffraction and differential thermal analysis were used to evaluate the physico-chemical reactions and phase changes in the obtained gels caused by heat treatment. Microstructural features, adhesion strength and corrosion resistance of the coated samples were determined by scanning electron microscope, microhardness, adhesion and electrochemical corrosion testing, respectively. The results showed that by increasing the sintering temperature from 350 to 550 C, the structure evolved from amorphous to crystalline state. For the first group of samples, sintering at 450 C and for second group, sintering at 550 C offered a more homogenous microstructure and improved corrosion resistance.