Kaka Ma
Department of Chemical Engineering and Materials Science
University of California, Davis

Nanostructuring of Metals/Alloys for Improved Performance

Location: EB1 Room 1011

Monday, February 2nd 2015 - 4:00 pm

The concept of nanostructuring has attracted the attention of researchers worldwide because of a variety of advanced material properties that can be achieved. Yet we are facing great challenges when it comes to the nanostructuring of complex engineering materials. In an effort to enhance the benefits of nanostructuring in real engineering materials, my research has been investigating the influence of nanostructuring on multi-component alloys for different applications. An approach of severe plastic deformation in powder metallurgy, cryogenic ball milling, was applied to fabricate nanostructured (NS) metallic powders. Two alloys were selected to elucidate how nanostructuring can change their microstructural development and therefore enhance their behavior compared with conventional counterparts. One is a NiCrAlY alloy used as the bond coat layer in a thermal barrier coating (TBC) system. This metallic bond coat retards the oxidation of the superalloy engine components by growing a layer of oxides, which is usually referred to as a thermally grown oxide (TGO), at the bond coat/top coat interface in the TBC. Nanostructuring of the metallic bond coat layer led to a distinct change in oxidation behavior of the entire TBC and contributed to its extended thermal cycling lifetime. Creation of a thermally stable, uniform distribution of ultrafine Al- or Y- rich oxide dispersoids within the bond coat layer, affects the Al outward diffusion from the bond coat to the bond coat/top coat interface, which ultimately influences the growth behavior of the TGO. The other complex engineering material under investigation is a precipitation strengthened Al alloy consisting of Al-Zn-Mg-Cu. This alloy is commonly used as a structural material for aircraft, for which mechanical behavior and dislocation activity are important. Nanostructuring not only improved the strength of this alloy but also altered its precipitation behavior. Reducing the grain size was noted to influence the dislocation substructure within the grain interior, which in turn governed precipitation kinetics. As a consequence, the precipitation strengthening was suppressed and grain boundary strengthening became the predominant mechanism.

North Carolina State University