Key Engineering Materials Vols. 434-435

Abstract: Ni-Mo coated TiC powders were prepared by electroless plating technique assisted by ultrasonic wave with hydrazine as reducing agent. The surface microstructure of the Ni-Mo coated TiC powders was characterized with scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results showed that the as-plated powders, which were of nearly spheric shape, were the composite of TiC and Ni-Mo alloy. The Ni and Mo elements were uniformly distributed around the TiC powders with some plating leakage. In addition, the Ni-Mo plated thin layers on the surface of TiC powders were amorphous or microcrystalline in a supersaturated state. Diffraction peaks corresponding to Ni and Mo weren’t found, and the Ti (NO3)4 and an unknown phase were formed as the load decreased from 15 g/L to 5 g/L.

Abstract: In this work, TiC-Ni coating was synthesized on copper substrate by electro-thermal explosion ultra-high speed spraying method at the discharge voltage of 26kV. Microstructure, phase structure, elemental distribution and microhardness of the coating were studied by means of scanning electron microscope in back-scatter-electron and secondary electron, energy-dispersive analysis X-ray spectroscopy, X-ray diffraction and Vickers hardness tester. The TiC-Ni coating, which exhibits no pores or cracks, consists of an irregular spheroidal TiC phase embedded in a nearly continuous Cu0.81Ni0.19 binder. TiC particles are uniformly distributed and the size of the TiC particle of the coating is less than 1.0 m because of the solute trapping effect. The average hardness of the TiC-Ni coating is approximately 1200 HV0.3.

Abstract: Micro-hardness measurements of thin coatings have to face the problem of the influence of the substrate. Based on relative method and the relationship between the composite hardness (the hardness of the coated sample) and the substrate hardness, a new model is proposed to evaluate the absolute hardness of ceramic coatings. Indentation tests with various load levels were carried out with specimens of (Ti,Al)xN1-x/SiyN1-y composite coating on SKH51 steel substrate. The results were analyzed by the new model and compared with those calculated by J-H (Jönsson and Hogmark) and L-C (Lesage and Chicot) models. The mean coating hardness obtained from this model shows similar results with the J-H model but a little higher than that from L-C model.

Abstract: Superhydrophobic surfaces, which have anti-adhesion and self-cleaning properties, were fabricated on Al substrates. The self-cleaning surface was prepared by two steps: firstly, a chemical solution method was used to create the surface roughness with disorderly veins micronanostructures. Secondly, fluoroalkylsilane was deposited on the rough surface to lower its surface energy. The combination of veins micronanostructures and fluoroalkylsilane modification gave the surface a superhydrophobicity with static water contact angle of 166° and sliding angle of smaller than 1°. Additionally, the surface showed a strong anti-adhesion with water and a satisfied self-cleaning property. Water droplets easily rolled off the surface and picked up dirt and debris with them. The surfaces obviously corresponded to Cassie (not Wenzel) -model. Air entrapped within the veins microstructures greatly increases the air/water interface, effectively preventing the penetration of water into the grooves, and finally exhibiting the self-cleaning property. The results will greatly extend Al substrates for specific functions such as water-repellence, self-cleaning and anti-fouling.

Abstract: Theoretical calculations suggest that creating superoleophobic surfaces would require a surface energy lower than that of any known materials. In the present work, we demonstrate micronanostructured ZnO-based surfaces displaying apparent contact angles (CA) greater than 150, even with hexadecane (surface tension l = 27.5 mN/m). The specific ZnO microtextures were fabricated by a chemical solution method, and fluoroalkylsilane (FAS) was then used to tune the surface wettability. The combination of ZnO microtextures and FAS modification resulted in a superoleophobicity with CA for hexadecane was 154.6 (161.9 for diethylene glycol (l = 45.2 mN/m). This apparent superoleophobic behavior was induced on intrinsically oleophilic materials mainly by topography (i.e. the specific ZnO microtextures), which form a composite surface of air and solid with oil drop sitting partially on air. Such special wetting state is a metastable Cassie state. The results are expected to promote the study on self-cleaning applications, especially in the condition with oil contaminations.

Abstract: Adhesion force measurements by atomic force microscopy (AFM) have been carried out to investigate the adhesion between the Si3N4 cantilever tip and the surface of the initial SiC-based Hi-Nicalon, Hi-Nicalon S, and Tyranno-SA fibers, as well as the ZrO2-coated and oxidized coated fibers. It was shown that the application of coating resulted in a change of the roughness parameters and a decrease of the adhesive forces between the Si3N4 cantilever tip and the fiber surface. Surface heterogeneity at the nanoscale could be responsible for the dispersion of adhesive forces. The results open the possibility of transferring nano mechanical information to meso or macro mechanical properties of ceramic matrix composites.

Abstract: TiO2/Multi-walled carbon nanotubes (MWNTs) were prepared via a wet chemical route with hydrolysis of titanium salts. The purification and oxidation treatment of MWNTs in concentrated HNO3 solution were conducted to modify the nanotubes. Then the pre-treated carbon nanotubes were added into the titanium salt and in the end the composites were formed. The microstructure of as-prepared TiO2/MWNTs composite was studied by TEM. The samples were calcined at different temperature. By X-ray diffraction (XRD), the phase transformation of nano-structured TiO2 in composites was determined. The photocatalytic activity of samples being calcined at different temperature was studied by using the conversion of methyl orange in aqueous solutions as probe reaction. The influence of the structure on photocatalysis efficiency was discussed. By contrast with that of pure TiO2 nanoparticles, the special structure of TiO2/MWNT composite could remarkably improve the efficiency of the photocatalytic reaction. The results indicated that the excited e- in conduction band of TiO2 might transfer into MWNTs and the possibility of the recombination of e-/h+ pairs decreased.

Abstract: The paper discusses the influence of processing parameters on the hardness of LD10 aluminum alloy coating treated by the power source with positive and negative pulse in the alkaline electrolyte. Lots of experiments were done with different processing parameters including positive current density, negative current density, frequency, duty ratio, processing time and electrolyte temperature, and the micro-hardness tester HVS-1000 was used to measure the coating hardness. The results indicate that elevating the duty ratio, or reducing the frequency can be advantageous to improve the coating hardness, and the coating is the hardest treated in electrolyte at the 30°C. And when the value of the positive and negative current density is reasonable, and the processing time rationally matches with the current density, the coating with HV2800 can be obtained.

Abstract: Flower-like NiO powders with nano-architectures, self-assembled nano-sheets, were synthesized using Ni (NO3)2•4H2O and urea in mix solvents of ethanol and water by homogeneous precipitation. XRD patterns showed that the NiO powders were of hexagonal structure. FESEM and TEM confirmed that the average diameter of the flower-like NiO was 10μm, and the ultra-thin nano-sheets had micro-porous structure, with the thickness less than 100nm and the size of 2μm×3μm. Specific surface area (BET) was around 130.92m2/g.

Abstract: In this work, Hertz indentation method was proposed to investigate the hardness, local strength and cyclic contact fatigue of brittle ceramic coating at high temperatures. The testing fixture for high temperature tests is designed, which is made of SiC. A Si3N4 ball with a diameter of 5 mm is used as the indenter and the CVD SiC/SiC composite is used as testing samples. The applied loads are ranged from 300 N to 700 N and the temperatures are among of room temperature to 1100 oC. The critical load and indent size are used to calculate the Brinell hardness and local strength of CVD SiC coating at room temperature and high temperatures. The contact damage under different loading number and period are analyzed. The mechanisms for the improved local strength and contact fatigue lifetime are discussed.