Ice-templated ceramic-metal composites modified by interfacial metal aluminates

Abstract

Interpenetrating phase (3-3) composites consists of two phases which are fully percolating throughout one system. Research efforts have been made towards routes to fabricate these composites that will allow for them to be utilized for applications like heat spreaders and leading-edge parts. Freeze-tape casting offers a potential avenue for developing 3-3 composites. The system can exhibit complete, long-range alignment through freeze-tape casting, in which both phases of the composite will be in constant periodicity of one another. To explore the potential of such ordering in 3-3 composites, ceramics, such as, yttria- stabilized zirconia (YSZ), alumina (Al 2 O 3) and zirconium diboride (ZrB 2) were freeze-tape casted and sintered to allow for second phase incorporation. Second phases, like copper (Cu) and silicon carbide (SiC) were utilized, so that ceramic-metal (cermet) freeze-tape casted composites and ultra-high temperature ceramic (UHTC) freeze-tape casted composites could be characterized. Initial composite property predictions were made using rule of mixtures (ROM). The work contained in this dissertation demonstrates that freeze-tape casted 3-3 composites can exhibit novel 3-axial anisotropic thermal behavior, and that, by ordering the percolating phases, high-temperature thermal behavior may be enhanced. This work, also, demonstrated that ceramic-metal interfaces are fragile, exhibiting thermal stress at the interface upon thermal cycling. Fostering interfacial adhesion between metal and ceramic phases is a primary tool for manipulating cermet properties. Common approaches to ceramic-metal joining include metallization and active brazing techniques. Though improvements in mechanical properties are notable, the functional capabilities can be sacrificed. To overcome these limitations, a novel approach, via a metal aluminate (copper aluminate), has been utilized to alleviate thermal stress along a ceramic-metal interface, and maintain adhesion of the ceramic-metal up to 100 psi. Mechanistically, it was not well- understood, as to what role copper aluminate played in modifying ceramic-metal interfaces. Chapter 5 of this work elucidates copper aluminate's role in fostering a ceramic-metal interface. By analyzing the surface and cross-sectional features of the cermet, it is discovered that through the formation of copper aluminate, porosity/roughness occurs to the bulk ceramic, allowing avenues for the metallic phase to penetrate through the thickness, fostering a mechanical interlocked joint.