The effect of vacuum heat treatment on microstructure, Al diffusion and thermal cycling lifetime of yttria stabilized zirconia by EB-PVD

The effect of yttria concentration (0-33.4 mol%), extraction rates (0.17, 0.33, 0.50, and 0.67 mm s-1), and the number of layers (up to four) on the phase content, surface defects, thickness, hardness, adhesion strength, and wear rate of yttria-stabilized zirconia coatings produced by sol-gel/dip-coating were studied for its use on thermolabile substrates. At 700°C, a metastable tetragonal phase ( t ″ ) was obtained even with 33.4 mol% yttria when heat treated for 24 hours; however, a fully cubic structure was attained by extending the heat treatment up to 48 hours as confirmed by Raman spectroscopy. Furthermore, it was necessary to use withdrawal speeds of at least 0.67 mm s-1 to produce defect-free coatings. Although the coatings were produced at low temperature, they showed 41% lower wear rate than steel and an adhesion strength of 30 MPa. Our work stresses the importance of the heat treatment history on the stabilization of the cubic phase in sol-gel YSZ coatings.

Download Full-text

Electrochemical and Oxidation Behavior of Yttria Stabilized Zirconia Coating on Zircaloy-4 Synthesized via Sol-Gel Process

International Journal of Corrosion ◽

10.1155/2013/453835 ◽

2013 ◽

Vol 2013 ◽

pp. 1-9 ◽

Cited By ~ 6

Author(s):

S. Rezaee ◽

Gh. R. Rashed ◽

M. A. Golozar

Keyword(s):

Heat Treatment ◽

Electrochemical Impedance ◽

Sol Gel ◽

Dip Coating ◽

Open Circuit ◽

Treatment Temperature ◽

Yttria Stabilized Zirconia ◽

Coated Sample ◽

Stabilized Zirconia ◽

Temperature Oxidation

Sol-gel 8 wt.% Yttria Stabilized Zirconia (YSZ) thin films were prepared on zirconium (zircaloy-4 alloy) by dip-coating technique followed by heat treating at various temperatures (200°C, 400°C, and 700°C) in order to improve both electrochemical corrosion and high temperature oxidation properties of the substrate. Differential thermal analysis and thermogravimetric analysis (DTA-TG) revealed the coating formation process. X-ray diffraction (XRD) was used to determine the crystalline phase structure transformation. The morphological characterization of the coatings was carried out using scanning electron microscopy (SEM). The electrochemical behavior of the coated and uncoated samples was investigated by means of open circuit potential, Tafel, and electrochemical impedance spectroscopy (EIS) in a 3.5 wt.% NaCl solution. The homogeneity and surface appearance of coatings produced was affected by the heat treatment temperature. According to the corrosion parameters, the YSZ coatings showed a considerable increase in the corrosion resistance, especially at higher heat treatment temperatures. The coating with the best quality, from the surface and corrosion point of view, was subjected to oxidation test in air at 800°C. The coated sample presented a 25% reduction in oxidation rate in comparison with bare substrate.

Download Full-text

Thermal Cycling Effect on Mechanical Properties of Yttria-Stabilized Tetragonal Zirconia

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.538.121 ◽

2013 ◽

Vol 538 ◽

pp. 121-124

Author(s):

Jing Zhang

Keyword(s):

Mechanical Properties ◽

Phase Transition ◽

Thermal Expansion ◽

Flexural Strength ◽

Thermal Cycling ◽

Tetragonal Zirconia ◽

Yttria Stabilized Zirconia ◽

Stabilized Zirconia ◽

Optical Applications ◽

The Stability

Yttria-stabilized zirconia (YSZ) is an important material in the area of energy and optical applications. In this study, the mechanical properties (Young’s modulus, Vickers hardness, flexural strength, and coefficient thermal expansion) and physical properties (phase transition) of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) was reported. The effect of thermal cycling on the mechanical properties and the stability was also evaluated.

Download Full-text