Low expansion metal matrix composites

Abstract

A low to near-zero metal matrix composite material featuring high modulus carbon fibers reinforcing a lightweight metal or semimetal. The fibers have a negative coefficient of thermal expansion in the axial direction. Laminates featuring parallel arrays of fibers may be cross-plied to produce quasi-isotropic properties in the composite body. The CTE of the composite body depends not only upon the relative CTE's of the fibers and matrix, and their relative amounts (e.g., loadings), but also upon the relative elastic moduli of the fibers and matrix. By intentionally introducing porosity into the matrix, the elastic modulus of the matrix is reduced, and thus the CTE of the composite body is influenced more by the CTE contribution of the fibers. In effect, the composite CTE is shifted toward that of the fibers, which shifting represents a reduction in composite CTE. Hydrogen outgassing upon solidification of the metallic matrix is one technique for producing such porosity.