Papers by Author: Zhang Jian Zhou

Abstract: Corrosion behavior of Fe-18Ni-12Cr-2.30Al and Fe-18Ni-12Cr-2.90Al-Nb-C austenitic steels was investigated in static Pb-Bi eutectic at 550 °C for 1000 h depending on the concentration of dissolved oxygen in the liquid metal. In the concentration range from 10¹² to 10⁸ mass % O, both steels underwent corrosion via dissolution resulted in the formation of spongy ferrite layer depleted in Ni and Cr and penetrated by Pb and Bi. In Pb-Bi with 10⁶ mass % O, Fe-18Ni-12Cr-2.90Al-Nb-C steel oxidizes with formation of very thin (≤ 1 μm) Cr/Al oxide film while Fe-18Ni-12Cr-2.30Al steel shows mixed corrosion behavior represented by more intensive oxidation and dissolution. The features of corrosion response are discussed depending on the composition of steels and concentration of dissolved oxygen in the Pb-Bi eutectic.

Abstract: The development of materials for core components which can serve in high temperature corrosive environments for a long service time is crucial to realize high efficiency and high-burnup operation of advanced nuclear reactors. Alumina forming austenitic (AFA) alloy is a kind of promising materials with improved corrosion resistance as well as strength at elevated temperature. The progress on the composition design and characterization of AFA alloys are reviewed in this work for evaluation their potential applications in advanced nuclear reactors. AFA alloys without the addition of carbon have been fabricated. Microstructures were observed by SEM and TEM. Mechanical properties were measured at room temperature and high temperature.

Abstract: Different coating technologies, such as plasma spray (PS), physical vapor deposition (PVD) and chemical vapor deposition (CVD), which can fabricate the PFM and join it to heat sink materials simultaneously, were applied for the fabrication of plasma facing materials (PFM) in fusion reactor. In the Institute of Nuclear Materials, University of Science and Technology Beijing (USTB), the concept of functionally graded materials (FGM) was adopted to fabricate coatings for effectively alleviating the thermal stress generated between coatings and the substrate materials under high heat flux loading (5~20 MW/m2). In the last several years, functionally graded coatings, including B4C/Cu, W/Cu and Mo/Cu systems were successfully fabricated by atmospheric plasma spray (APS). Characterization of coatings was performed in order to assess microstructure, mechanical properties and high heat flux properties of the FGM coatings. Furthermore, a high thick tungsten coating with 4 mm on copper – chromium - zirconium (Cu, Cr, Zr) alloy substrates was fabricated by APS. The porosity of the coating is less than 2% while mean tensile strength of the coating is about 7 MPa. However, the content of oxygen in the coating is about 6 wt% by energy dispersive spectrum (EDS) analysis, thus further optimization is necessary.

Abstract: Two kinds of W/Cu functionally graded material based high heat flux components, including monoblock concept and flat tile concept, are designed and fabricated. Thermally induced stresses and strains under operation conditions in these components are analyzed using finite element analysis. The effect on stress and strain of using different graded structures to join Cu to W is examined and compared. There has no obvious difference on operation thermal stress mitigating between monoblock design and flat tile design. The component with monoblock concept was fabricated by a one step fast resistance sintering, and the component with flat tile concept was fabricated by infiltration-welding method successfully.

Abstract: Molybdenum has many prominent properties, such as high melting point, good thermal properties, low erosion rate and so on, which make it promising candidate materials for plasma facing materials in the next fusion reactor. In the present work, molybdenum coatings were deposited onto the oxygen-free copper substrates by atmospheric plasma spraying. Different interlayers were introduced between the coatings and substrates. SEM, EDS and XRD were used to investigate the photographs and compositions of these coatings. The bonding strength of the coatings was tested to investigate the effect of interlayers on adhesion of the coatings at room temperature and it was found that the coating without interlayers showed the highest bonding strength. Water quenching method was used to evaluate the adhesion of the coatings under thermal cycling conditions and the results showed that the molybdenum coating with two interlayers possessed of the highest resistance of thermal cycling wrack.

Abstract: Tungsten has been decided as the plasma facing material (PFM) for some high heat flux regions of the divertor in the International Thermo-Nuclear Experimental Reactors (ITER). In this paper, our efforts concentrated on the functionally gradient W/Cu coating fabricated on the oxygen free copper by atmosphere plasma spraying under the inert gases protection. The functionally gradient W/Cu coatings were designed to relieve the thermal stress during the spraying processes. For comparison, the tungsten coatings were also deposited directly onto the copper substrates by the same technology. XRD, SEM and EDS were applied to identify the phases, morphologies and compositions of these coatings. Tensile tests were performed to measure the bonding strength between the coatings and the substrates. Furthermore, water quenching and high heat loading experiments using a pulse laser beam were also carried out to estimate the thermal shock properties of these coatings.

Abstract: This paper reports some new progresses on layered and graded coatings for plasma facing materials in fusion devices in Laboratory of Special Ceramics and Powder Metallurgy (LSCPM), University of Science and Technology Beijing (USTB), China. They included tungsten coatings made be various particle sizes of initial feedstock and interlayers and boron carbide graded coatings. All the coatings were fabricated on the oxygen free copper by plasma spraying. The microstructures and properties were investigated for PFM. Water quenching and high heat loading experiments were also carried out to estimate the thermal performance of these coatings.

Abstract: Several kinds of ceramic powders including SiC, TiO2 and Al2O3 were selected as fillers blending with epoxy resin, curing agent and other additives to prepare a heavy-duty and anti-wear coating. The effects of filler sort, powder size, dispersion homogeneity on the coating properties were investigated. The results showed that the wear resistance and corrosion resistance of the coating could be improved significantly after meliorating the dispersion of the ceramic particles in epoxy resin. Other mechanical properties were also studied in order to support the view on the positive effect of the nano-particles in the epoxy coating.

Abstract: Molybdenum has many prominent properties, such as high melting point, good thermal properties, and low erosion rate and so on, which make it promising candidate materials for plasma facing materials in the next fusion reactor. In this paper, Molybdenum coatings were deposited onto the oxygen-free copper substrates by atmospheric plasma spraying. The spraying parameters had been carefully selected. Different interlayers were induced between the substrate and the coating. SEM and XRD were used to investigate the photographs and compositions of these coatings. The micro-hardness and bonding strength were also tested. Thermal behaviors of the coatings were evaluated by thermal shock tests. The coatings with interlayers showed better resistance of thermal shock but lower bonding strength compared to coatings that without interlayers.

Abstract: Tungsten has the highest melting point among all metal, which makes it withstand thermal shock and erosion in high temperature environments. In this study, Tungsten coatings were sprayed onto the oxygen-free copper substrates by plasma spraying using inert gases protection. XRD, SEM and EDS were used to identify the phases, morphologies and compositions of the coatings. Vickers micro-hardness and bonding strength of the tungsten coatings were also measured. The results revealed that the hardness distribution of the tungsten coatings was different along the thickness direction. The tungsten coating without any interlayer showed higher bonding strength than that of the other two coatings with NiCrAl and W/Cu interlayers, respectively.