Surface composites: A new class of engineered materials
- PDF / 473,984 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 204 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Surface composites: A new class of engineered materials Rajiv Singh and James Fitz-Gerald Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (Received 17 June 1996; accepted 5 August 1996)
To integrate irreconcilable material properties into a single component, a new class of engineered materials termed “surface composites” has been developed. In this engineered material, the second phase is spatially distributed in the near surface regions, such that 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 bulk composites, the surface phase in surface composites is present only at the near surface regions. In contrast to FGM, 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 cone-like structures. The laser induced micro-rough structures (LIMS) possess surface areas which are up to an order of magnitude higher than the original surface. 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, compositionally and thermally graded interface, which gives rise to improved adhesion of the surface phase. Examples of various types of surface composites such as WyMo, silicaySiC, diamondysteel, etc. are presented in this paper. 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-polymeric joints.
I. INTRODUCTION
In today’s highly demanding technology environment, one of the main challenges in materials design and processing is combining irreconcilable properties of materials in the same component, such as high strength at high temperatures with structural toughness.1–4 Engineered materials such as bulk composites and functionally graded materials (FGM) have been developed to combine desirable materials properties into a single component. A schematic diagram depicting the cross section and top view of bulk composites and FGM is shown in Fig. 1. The composite materials, which are mainly used in structural applications, are generally composed of ceramic, metal, or polymeric matrix with a dispersed second phase. To develop useful bulk composite microstructure, the reinforcement phase should be uniformly dispersed and should possess chemical, thermal, and interfacial compatibility with the matrix. In FGM, the chemical composition is varied either continuously or discontinuously across the thickne
Data Loading...
