Variable-density composite articles, preforms and methods

A method for making a metal matrix composite article, comprising:

• providing a porous preform comprising a first end, a second end, an outer surface, and a first reinforcement component, the first reinforcement component comprising a density increasing between the first end of the preform and the second end of the preform according to a first gradient;
• positioning the preform within a die cavity;
• introducing a molten metal matrix composite material into the die cavity about the preform, the metal matrix composite material comprising a liquid component and a second reinforcement component;
• pressurizing the molten metal matrix composite material, thereby
• infiltrating the preform with at least the liquid component, and
• forming a distribution of the second reinforcement component adjacent to the outer surface of the preform, the distribution of the second reinforcement component comprising a density increasing in a direction toward the outer surface of the preform according to a second gradient.

A method for making a variable-density preform, comprising:

• providing a preform slurry comprising a liquid component, at least a first reinforcement component, and a first density;
• depositing a first layer of the preform slurry at the first density onto a working surface;
• changing the density of the preform slurry from the first density to a second density;
• depositing a second layer of the preform slurry at the second density on top of the first layer of the preform slurry;
• removing the liquid component from the preform slurry as it is deposited on the working surface;
• and
• drying the layers of the preform slurry deposited on the working surface to remove residual amounts of the liquid component;
• wherein the first and the second layers of the dried preform slurry comprise a reinforcement density gradient corresponding to the first density and the second density.