Abstract: High current pulsed electron beam (HCPEB) is now becoming a promising energetic source for the surface treatment of materials. When the concentrated electron flux transferring its energy into a very thin surface layer within a short pulse time, superfast processes such as heating, melting, evaporation and consequent solidification, as well as dynamic stress field induced by an
abrupt thermal distribution in the interactive zone impart surface layer with improved
physicochemical and mechanical properties. The present paper reports mainly our experimental research work on this new-style technique. Investigations performed with a variety of constructional materials (aluminum, carbon and mold steel, magnesium alloys) have shown that the most pronounced changes of composition, microstructure and properties occur in the near-surface layers, while the thickness of the modified layer with improved mechanical properties (several hundreds of
micrometers) is significantly greater than that of the heat-affected zone due to the propagation of stress wave. The surfaces treated with either simply several pulses of bombardment or complex techniques, such as rapid alloying by HCPEB can exhibit improved mechanical and physicochemical properties to some extent.
Abstract: The effects of two silane coupling agents (KH550, KH570) and three coupling agents of organic titanate (JSC, CT136 and NTC401) on the surface modification of superfine Al2O3 powders were tested and compared. The results showed that three coupling agents of organic titanate succeeded in modify the surface of Al2O3 particle from hydrophilic property to lipophilicity, while two silane coupling agents failed. The group changes of the surface were confirmed by IR spectrum,
which also indicated that chemical absorption occurred between NTC401 and the powders surface, but for JSC and CT136 mainly occurred physical absorption. SEM photos of the powders showed that agglomeration-free particles could be obtained when the powders were treaded by NTC401. However, when treated by JSC or CT136 the powders tended to be secondly agglomerated. The proper coupling mechanism was analyzed, and it was thought that space structure of octahedral complex of titanium ion with six ligands could effectively impede agglomeration.
Abstract: Metal ions were implanted into the surface of fiber with metal vapor vacuum arc source implanter. The resin matrix composite was made of the surface modified fibers. The microwave absorbing property of the composite was measured. It is shown that the microwave absorbing property of the composite was improved effectively by the ion implantation and the extreme reflectivity reached -6.13dB. The paper studied the microwave absorbing property of the composite material treated by ion impregnation and discussed mechanism.
Abstract: Thermal barrier coatings (TBCs) with the ceramic coats of hollow spherical
ZrO2-8%Y2O3 powder (HSP-YSZ) were obtained on Ni-base superalloy by detonation gun (D-gun) spraying. Thermal shock cyclic tests were performed by holding samples at 1100°C for 10 min and then water quenching to room temperature repeatedly. The D-gun sprayed TBCs didn’t fail up to 300 cycles and exhibited excellent resistance to thermal shock. Failure mechanism of D-gun sprayed
TBCs subjected to thermal shock cycling was discussed.
Abstract: This paper introduced the structure of the high efficiency hypersonic plasma spraying gun and the effects of hypersonic plasma jet on the sprayed particles. The optimised spraying process parameters for several ceramic powders such as Al2O3, Cr2O3, ZrO2, Cr3C2 and Co-WC were listed. The properties and microstructure of the sprayed ceramic coatings were investigated. Nano Al2O3-TiO2 ceramic coating sprayed by using the high efficiency hypersonic plasma spraying was also studied. Compared with the conventional air plasma spraying, high efficiency hypersonic plasma spraying improves greatly the ceramic coatings quality but at low cost.
Abstract: The as-sprayed zirconia coating had an average grain size of 67 nm. Thermal treatment results showed that the grains of the nanostructured coating grew slightly below 900°C, whereas over 1000°C the gains grew rapidly. The thermal diffusivity of the coating increases with increasing heat-treatment temperatures.
Abstract: Using a special impulse device, the impulse electroless Ni-P alloy plating were
prepared. The microstructure、crystallization and the starting activation energy for crystallization was investigated by TEM、XRD and DTA, compared with electroless Ni-P alloys plating. The results showed that the diffractive ring was wider when using impulse, depositing temperature dropped up to 65°C,and crystallization temperature rose up to 310°C. Furthermore , the starting activation energy for crystallization and crystallization temperature of impulse electroless Ni-P
alloys plating measured were more than that of electroless plating in the heating rate at 5、10、20、 40K/min, and it was also higher in the amorphous disorder degree and the starting crystallization temperature. Impulse electroless Ni-P alloys plating had better performance of thermal stability.
Abstract: It is generally believed that the failure of TBCs is attributed to the spallation occurred in the ceramic coat. The spallation is closed linked with sinuate morphology factors, including its amplitude and period, at the TGO/bond coat interface. In this work, dependence of the residual stress distribution on the sinuate morphology in the TBCs has been studied by means of Finite Element Method (FEM) simulation for isothermally annealed specimens. The simulation results indicated that the maximum value of residual stress existed inside the TGO layer. It was also found that the
maximum residual stress occurred at different points, near the TGO/bond coat interface at the peak of the sinuate interface, while near the TGO/ceramic coat interface at the valley, respectively. And the maximum residual stress increased with increasing the ratio of the amplitude to period in the sine morphology, which has been proved by the thermal cycle experimental results.
Abstract: Two layer thermal barrier coatings (TBCs) were prepared by EB-PVD (Electron
Beam-Physical Vapor Deposition) at different substrate temperatures in the range of 823 to 1123K, and their microstructure was investigated with SEM and AC impedance as a function of substrate temperature and thermal cycling time. YSZ layer of all TBCs samples is in column structure, but the grain size and growth orientation are different with substrate. In this research, impedance spectra (IS)
was measured as a function of thermal cycling between 1323K and 298K for these thermal barrier coatings. Grain boundary and bulk can be distinguished from analysis of AC impedance spectroa to provide information about the relation between microstructure and electric properties.The change in IS until failure was found to be related with the thickness, microcracks and macrocracks of TGO and
the change in the interfacial of TGO/YSZ.