Ceramic preforms having high mechanical strength, a process for their preparation and metal matrix composites obtained from said ceramic preforms

Claim 1

A ceramic composite consisting of ceramic fibrous material bound chemically by one or more nitride ceramic phases having a density ranging from 0.2 to 1.6 g/cm 3 , porosity ranging from 50 to 95% and ultimate bending strength over 5 MN/m 2 obtained by a process comprising: a) preparing a dispersion in a liquid base containing a ceramic fibrous material and a finely particled metal powder, a polymeric binding agent and, optionally, a dispersing and/or plasticizing agent; b) preparing elemental units by pouring the dispersion through a system orienting the fibrous material in a uniaxial way; c) evaporating the liquid base from the poured elemental unit; d) forming a semi-finished product by overlapping and pressing more evaporated elemental units, according to thicknesses and profiles for the composite to be formed; e) treating the semi-finished product for the degradation and/or debinding of the binding agent; and f) heating at a high temperature, in the presence of a flow of nitriding gas, the product obtained in step e); the weight ratio between the metal powder and the ceramic fibrous material ranging from 0.05 to 5, and the amount of binding agent ranging from 0.5 to 20 weight %, based on the whole composition.