Papers by Author: Chuang Dong

Abstract: Thermal stability, adhesion and electronic resistivity of the Cu alloy films with diffusion barrier elements (large atom Sn and small atom C) have been studied. Ternary Cu (0.6 at.% Sn, 2 at.% C) films were prepared by magnetron co-sputtering in this work. The microstructure and resistivity analysis on the films showed that the Cu (0.6 at.% Sn, 2 at.% C) film had better adhesion with the substrate and lower resistivity (2.8 μΩ·cm, after annealing at 600 °C for 1 h). Therefore, the doping of carbon atoms makes less effect to the resistivity by decreasing the amount of the doped large atoms, which results in the decreasing of the whole resistivity of the barrierless structure. After annealing, the doped elements in the film diffused to the interface to form self-passivated amorphous layer, which could further hinder the diffusion between Cu and Si. So thus ternary Cu (0.6 at.% Sn, 2 at.% C) film had better diffusion barrier effect. Co-doping of large atoms and small atoms in the Cu film is a promising way to improve the barrierless structure.

Abstract: The thermal stability and glass-forming ability (GFA) of Zr70Ni30−xAlx (x = 5 − 19) metallic alloys were investigated. Alloy with x = 8 has the largest critical diameter (dc) of 2 mm in the alloy series, which possesses the largest supercooled liquid region, Trg and γ value, simultaneously. Further addition of 2 − 4 at.% Nb to Zr70Ni22Al8 alloy by replacement of Zr increases the dc up to 6 mm. In addition, Zr70Ni22Al8 bulk metallic glass exhibits large compressive plastic strain of 13.8% with yielding stress of 1547 MPa and Young’s modulus of 79 GPa. Addition of Nb increases the strength but lowers the plasticity.

Abstract: [(Mo,Sn)(Ti,Zr)₁₄]Nb₁ serial alloy compositions were designed using a cluster-plus-glue-atom model to receive BCC β-Ti alloys with low Youngs modulus (E) in Ti-based multi-component systems, where the square brackets enclose the coordination polyhedron cluster CN14 of the BCC structure and Nb is the glue atom. These serial alloys were prepared into rods with a diameter of 6 mm by copper-mould suction casting method. XRD and tensile test results indicated that all these alloy series possessed a monolithic BCC structure except [SnTi₁₄]Nb₁ and [(Mo_0.5Sn_0.5)Ti₁₄]Nb₁ due to Sn deteriorating BCC structural stability. A combination of Mo_0.5Sn_0.5 at the cluster center, as well as low-E Nb and Zr in the glue and cluster shell respectively, can reach simultaneously low E and high BCC stability, incarnated in the [(Mo_0.5Sn_0.5)(Ti₁₃Zr)]Nb₁ alloy which has the lowest E of 48 GPa in the suction-cast state.

Abstract: Thermal barrier coatings are used as thermal insulation and thermal protection for high-temperature components of aircraft engines. Service failure of the components is often caused by premature breaking of the coatings. The distributions of residual stress in a ZrO₂/NiCoCrAlY thermal barrier coating during thermal cycling was here simulated using finite element method. Four kinds of models involving planar and curved interfaces between the bond and the ceramic top coat layers were established. The simulated results showed that the high residual stress which is about 100-300MPa is present at the interface between bond layer and ceramic layer. The residual stress in curved interface is larger than that in planar one, and concentrates mainly at the troughs. Structure for planar interface exhibits better than curved interface. The residual stress would increase obviously with the presence of thermally grown oxide layer.

Abstract: The surface irradiation of 6063 aluminum alloy by high current pulsed electron was conducted with the aim of replacing the complicated pre-treatment in the processes of electroless plating. To explore the microstructure changes, optical metallography, SEM (scanning electron microscope), XRD (X-ray diffraction) analyses were carried out, and the sliding tests were used for the detection of wear resistance. It was concluded that the HCPEB irradiation could replace the pre-treatment of aluminum substrate as required in conventional electroless plating with a decreased surface roughness of Ni-P alloy plating layer. The plates exhibited an amorphous microstructure as demonstrated by XRD analysis. The plates, produced with the routine of HCPEB irradiation, activation and electroless plating possess, also exhibited good quality, even better than that of conventional electroless plating technique.

Abstract: With the aid of the atomic-cluster-plus-glue-atom model (ACPGA model) proposed by Dong et al [1] for bulk metallic glasses (BMGs), the formation and characteristic of Ni-Ta binary BMGs were investigated in this work. Binary glass-forming compositions containing 56.3–62.5 at.%-Ni were obtained by a composition formula [M-Ni₆Ta₆]Ni₃ based on the ACPGA model. It was found that Ni-Ta BMGs with a diameter of 2 mm was obtained over a composition range of 59 ~ 62 at.%-Ni by copper mold casting method, which are in good agreement with our model prediction. Newly-developed Ni–Ta BMGs are a kind of extreme materials, which exhibit superior thermal stability (T_g = 993K) and a ultrahigh fracture strength of about 3.5 GPa.

Abstract: The present paper presents the first results of an ongoing research dedicated to the analysis of microstructure in steels surfaces treated by Low Energy High Current Pulsed Electron Beam (LEHCPEB). Various steels - 316L (a stainless steel), D2 (a cold-worked die steel) and 4Cr13 (a martensitic steel) - have been treated by LEHCPEB in order to improve the understanding of the surface microstructure modifications induced by this treatment. The microstructures in the modified surface were characterized by microscopy and diffraction techniques.

Abstract: High current pulsed electron beam (HCPEB) has been developed as a useful tool for surface treatment of materials. In the present work, the fundamental principle of HCPEB source was described along with the device configuration and working parameters. Through the different kinds of HCPEB surface treatment experiments conducted, the enhanced surface properties induced by HPCEB treatment were illustrated and explained with their microstructure characterization results.

Abstract: High current pulsed electron beam (HCPEB), a novel high-power energetic beam technology, has been developed as a useful tool for surface modification of materials. In the present work, the effect of HCPEB treatment on microstructure and wear resistance of Al-15Si and ZK60-1Y Mg alloys was investigated. The results show that a supersaturated solid solution of (Al) and (Mg) is formed on top surface of melted layer induced by rapid heating and cooling during HCPEB process. In addition, the melted layer of approximately 5~11μm thickness is obtained on the ZK60-1Y Mg alloy surface. Wear resistance of Al-15Si and ZK60-1Y Mg alloys are significantly improved after HCPEB treatment. It is demonstrated that HCPEB technology has a good application future in enhancing surface properties of Al-Si and Mg alloys.

Abstract: The low energy high current pulse electron beam (LEHCPEB) irradiation induces ultra fast dynamic temperature fields in the surface of the material to which is associated dynamic stress fields that causes intense deformation at the material surface and sub-surface. Improved surface properties (hardness, corrosion resistance) can be obtained using the LEHCPEB treatment. Under the “Melting” mode, the top surface (few µm) which is melted and rapidly solidified (107 K/s), can solidify has nano-domains formed from the highly under-cooled melt. The thermal stress wave that propagates in the sub-surface imposes strain hardening and grain size refinement. This induces a sub-surface hardening that can extent over about 100 µm. The use of the “Heating” mode is less conventional. This mode can promote grain size refinement, hardening as well as texture modification without modification of the sample geometry.