Surface composites: novel method to fabricate adherent interfaces

Abstract

To integrate irreconcilable material properties into a single component, novel engineered materials termed ‘surface composites’ have been developed. In these engineered materials, the second phase is spatially distributed in the near surface region, whereas the phase composition is linearly graded as a function of distance from the surface. Surface composites are different from existing engineered materials such as bulk composites and functionally graded materials (FGM). Unlike in bulk composites, the surface phase in surface composites is present only in the near surface region. In contrast to FGMs, the graded properties of surface composites are achieved by unique morphological surface modification of the bulk phase. To fabricate surface composites, the initial surface of the bulk material is transformed using a novel multiple pulse irradiation technique into truncated conelike structures. The laser induced microrough structures possess surface areas which are up to an order of magnitude higher than that of the original sUljace. The second phase is deposited on the surface using thin or thick film deposition methods. A key characteristic of surface composites is the formation of a three-dimensional, compositonally and thermallygraded interface, which gives rise to improved adhesion of the surface phase. Examples of various types of surface composites such as W/Mo and diamond/WC–Co are presented. The unique properties of surface composites make them ideal engineered materials for applications involving adherent thick film coatings of thermally mismatched materials, compositional surface modification for controlled catalytic activity, and creating adherent metal–ceramic and ceramic–polymer joints.