Papers by Author: Zhi Ping Wang

Abstract: Ni-20wt.%Al coating was fabricated on the 6061-T6 aluminum alloy substrate in twin wire arc spraying technology. Heat treatment temperature was 400°C，480°C and 550°C, and each heat treatment time was 4h, 24h and 48h. Reaction mechanism and diffusion behavior of elements of coating/substrate interface were discussed. The XRD results showed that NiAl and Ni3Al phases were diminished and the nickel solid solution was gradually improved in volume. And some oxide phases existed, such as two types of alumina and nickel oxides. The SEM and EDS analysis showed, there was no obvious diffusion. At the low temperature condition, the diffusion phenomenon was existed in the interface.

Abstract: The nanocrystalline surface was obtained on bulk pure nickel by using high-current pulsed electron beam (HCPEB) technique. The temperature field induced by HCPEB was numerically simulated. The structures of the nanocrystallized surface were characterized by scanning electron beam (SEM), which showed that after HCPEB irradiation, the initial coarse-grained structure on the surface was refined into fine grains with sizes of about 70nm. It was revealed that melting surface caused by HCPEB irradiation and subsequently rapid cooling was the dominant mechanism of the surface nanocrystallization of bulk nickel. The HCPEB technique provides a new method for rapid fabricating surface-nanocrystallized materials.

Abstract: Thermal barrier coating (TBC), which consisted of a NiCoCrAlY bond coat (BC) and a ZrO₂-8 wt.%Y₂O₃ topcoat (TC), was fabricated on the nickel-base superalloy by air plasma spray (APS). The BC and TBC was treated by vacuum heat treatment (VHT). The oxidation of coating with and without VHT has been performed at 1050°C. Oxidation behavior of coatings and thermally grown oxide(TGO) scale were studied by SEM with EDS. As shown in the results, after treating by VHT, a continuous Al₂O₃ layer formed more rapidly on the VHT coating than that formed on the APS coating, which can act as a diffusion barrier to suppress the formation of other detrimental oxides. The pre-oxidation treatments reduced the growth rate and extend the steady-state growth stage. The TGO in VHT TBC was still a single layer Al₂O₃ oxide after 120h. However, after same oxidation time, the TGO in APS TBC produced a dual-layer oxide consisting of an inner Al₂O₃ layer and outer spinel layer. Therefore the VHT improves the oxidation resistance of APS coating.