Kai Ming Liang

High-Temperature Oxidation Behavior of the Co-Base Superalloy DZ40M in Air

The oxidation behavior of the Co-base superalloy DZ40M was studied in air at900–1100°C for times of up to 2000 hr. The results indicated thatthis alloy can grow a protective oxide scale at 900 and 1000°C duringisothermal oxidation, but not at 1100°C because of serious cracking andspalling of the oxide scales. Moreover, an internal-precipitate zone formedin the subsurface region of the alloy at all temperatures and times. Theprecipitates were rich in Cr in the vicinity of the alloy–scaleinterface and rich in Al deep in the alloy. The internal-precipitatemorphology changed from a granular to needlelike shape with increasingoxidation temperature.

Failure behavior of an aluminide coating on a Co-base superalloy during high-temperature oxidation in air

A surface-morphology change has been observed for an aluminide coating on the Co-base superalloy DZ40M during oxidation at 1100°C in air. The oxide formed on the coating remained an even grayish-white color during the stable oxidation stage, whereas, dark-colored corrosion nodules were observed when oxidation of the coating accelerated. The number of nodules increased with time, along with growth of the nodules, eventually covering the entire surface which signified failure.

Using theoretical formulae to calculate degradation life for an aluminide coating during high-temperature oxidation in air

A formula which describes the life of high-temperature oxidation for aluminide coatings is applied in this paper. With this formula, the longer life of coatings at the lower temperature can be evaluated from the shorter life of coatings at the higher temperature. Also, the degree of degradation of coatings at different temperatures for any given time can be deduced from that at two given temperatures. In the present work, this theoretical formula is used to calculate the oxidation life for the aluminide coating on a new Co-base superalloy at a given temperature, and the calculated result is shown to be practical by the relative oxidation kinetic curve.

Oxidation behavior and breakdown of an aluminide coating on DZ40M alloy at high temperatures

DZ40M alloy is a new Co-base superalloy, which is suitable for the blade material of gas turbines. In this paper, isothermal oxidation of an aluminide coating on this alloy was examined at 900–1100°C in air. It was observed that the weight gain at lower temperatures (900 and 1000°C) was greater than that at the higher temperature (1050°C), which was due to the formation of both θ-Al2O3 and α-Al2O3 at 900 and 1000°C but only α-Al2O3 at 1050 and 1100°C.

Study on the Cracking of SiO2-TiO2 Films Prepared by Sol-Gel Method

In this paper, the cracking behavior of sol-gel-derived SiO2-TiO2 films on glass-ceramics substrates is characterized by means of DTA, XRD and SEM. The SiO2-TiO2 films are deposited by sol-gel dip coating with tetrabutyl orthotitanate (Ti(OBu)4) and tetraethyl orthosilicate (TEOS) as raw precursors. The result shows that the cracking of the films is mainly related to the surface cleanliness of the substrate, the thermal expansion coefficients of the film and the substrate, the viscosity of the mixed sol, and the unbalanced stress produced during drying and heating process. The films without cracks were obtained by modifying the composition of sol and controlling the relative humidity and the heating rate of heat treatment.

Crystallization of Cordierite-Based Glass-Ceramics Adding with Fe2O3-TiO2

The effect of Fe2O3-TiO2 mixture additives on the crystallization behaviour of a parent glass with composition located in the primary field of cordierite within the MgO-Al2O3-SiO2 system has been examined. The crystallization behaviour of the glass was determined by differential thermal analysis (DTA) and X-ray diffraction (XRD). The microstructure was characterized by scanning electron microscopy (SEM). The results show that additives of Fe2O3-TiO2 can lower the temperature of the crystallization peak (Tp) and promote crystallization of the parent glass. By controlled thermal treatment, the main crystal phase obtained was Fe2+substituted α-cordierite. The approach outlined in this paper to obtain heterogeneous ion substituted cordierite glass-ceramics is useful to develop infrared radiation material with good properties.

Nucleation and Crystallization of Glass-Ceramics from Coal Fly Ash

The nucleation and crystallization kinetics of glass obtained by melting coal fly ash with additives at 1550°C have been investigated. The optimum heat treatment schedule for the glass was nucleation at 825°C for 60min before crystallization at 962°C for 4h. The activation energy for crystallization of the glass-ceramics, obtained by the DDTA result, was 280.03 kJ/mol, lower than that of glass-ceramics obtained from pure reagents. The low activation energy is caused by impurities in fly ash, serving as nucleation agent. The results of XRD and SEM show that glass-ceramics developed nano-sized spherical wollastonite.

The Effect of Zirconia Sol-Gel Coatings on Mild Steel Oxidation Resistance

The effect of zirconia coatings deposited by the sol-gel technique on the oxidation of mild steel was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and measuring weight gain. It was found that the thickness of zirconia coatings is a crucial factor affecting the oxidation kinetics and the multilayer dip–coating is much more effective than the single coatings. Auger electron spectroscope (AES) was used to evaluate the depth composition of scale. The results suggest that the growth mechanism of the oxide scale for coated mild steel change from outward cation to inward anion diffusion, during oxidation.

Crystallization Behavior of Mg-Doped Titania

The Mg-doped TiO2 was prepared by Sol-gel method at low temperature. The crystallization of TiO2 was studied by DTA, it was shown that the phase transition temperature of the Mg (NO3)2-doped TiO2 from amorphous to anatase and then to rutile significantly reduce. The XRD results show that the Mg-doped TiO2 has anatase and rutile annealed at 600 °C. Studies of photo-catalytic degradation show that the photo-catalytic activity of Mg-doped TiO2 thin film is higher than that of non-doped TiO2.

Phase Transformation Behavior of ZrO2-TiO2 Thin Films in Electric Field

ZrO2-TiO2 thin films, which were heat-treated with an applied electric field, were prepared by sol-gel method. The phase transformation behavior of ZrO2-TiO2 composite thin films was studied by DTA, XRD, SEM and Raman spectroscopy. In an electric field, the phase transformation temperature of amorphous phase to anatase and that of anatase to rutile are all decreased.