Jiuba Wen

Effect of Rare Earth on Void Band of Diffusion Layer and Properties of Aluminized Steel

The effects of the addition of rare earth (RE) elements on the void band in the diffusion layer, and the resistances to both oxidation and spalling of aluminized steel were investigated through high temperature oxidation and spalling tests. The results showed that RE had significant effects on the void band in the diffusion layer and the properties of aluminized steel. After diffusion treatment, a considerable number of the voids between the middle layer and transitional layer of pure aluminized coating, aggregated into wavy-line- shaped void bands parallel to the outer surface. For the RE-added aluminized coating, only a few voids aggregated into intermittent block shapes. During high temperature oxidation at 800 °C for 200 h, the wavy void band of pure aluminized coating aggregated further into a linear crack parallel to the outer surface, and the internal oxidation occurred within them; the open cracks perpendicular to the surface penetrated through the diffusion layer. For the RE-added aluminized coating, only a few voids aggregated into intermittent meniscus shapes. During cyclic spalling tests, the peeling, spallation, and pulverdent cracking occurred along the void band in the diffusion layer of pure aluminized coating, but only a little spallation occurred in the diffusion layer of the RE-added aluminized coating, in which cracks perpendicular to the surface were much smaller than those of pure aluminized coating and did not penetrate through the diffusion layer. It is evident that RE addition can restrain the formation and aggregation of voids and subsequently improve the resistances to oxidation and spalling. The mechanism of the RE effect on the void band in the diffusion layer is also discussed.

Preparation and Electrochemical Properties of NiO Thin Films by Sol-Gel

The NiO thin film was deposited on the stainless steel substrate by spin-coating compared with thermal treatment technique. Thermal decomposition behavior of gel precursor, the structure, morphology and electrochemical properties of NiO thin film were characterized by thermogravimetric/differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and constant current charge-discharge techniques. The results show that the stable sol is synthesized by nickel acetate and PAA. The gel precursor completely decomposes and gradually forms the nanocrystalline NiO at 450°C during the sintering. The crystal structure of NiO films become more integrity and particles large with the increasing of sintering temperature. The morphology and structure of the NiO thin film sintered at 500°C for 2h is perfect and exhibits high discharge specific capacity and well cycle performance whose initial and stable discharge capacity after 20 cycles are 1147.5mAh/g and 741mAh/g , respectively.

The activation energy of superplastic flow above the critical temperature for steel CrWMn

By means of superplastic tensile test above the Ac1 temperature (γ→α transformation temperature), superplastic deformation activation energy of ultrafine-grained commercial die steel CrWMn is investigated on the basis of the Arrhenius theory equation, exp( / ) 1 ε& = Aσ m −Q RT , which indicates the resistance of the superplastic deformation. According to the Arrhenius equation, the activation energy is estimated from the log σt vs 1/T relationship at a constant of sensitivity index of strain rate. The results show that the strain rate sensitivity index is a constant and rather high at the conditions of superplastic deformation for the CrWMn steel, the activation energy for superplastic deformation of steel CrWMn above the critical temperature is 187KJ/mol, and the superplastic deformation activation energy is approached to the grain boundary diffusion activation energy of γ-Fe. This indicates that the grain boundary sliding (GBS) in superplastic deformation of CrWMn steel is controlled by grain boundary diffusion. The characters of superplastic deformation of the steel above the critical temperature, on the other hand, are also analyzed in this paper.

Activation Energy for Superplastic Flow Above Critical Temperature of Die Steels

Some commercial cold working die steels GCr15 and CrWMn with ultra-fine grain size were chosen as tested materials to research the activation energy for superplastic flow at different temperatures and strain rates above critical temperature. Based on the Arrhenius equation, the activation energy for superplastic flow is evaluated. The activation energy at constant strain rate is estimated by the logσtvs 1/T relationship. The results show that the activation energy is usually small under the conditions of optimal flow. The characteristics of superplastic deformation of steels above the critical temperature were also analyzed.