Composite by infiltration

A polycrystalline composite comprised of a ceramic member in an amount ranging from about 15% by volume to about 65% by volume of the composite and a fluoride-containing member in amount from about 35% by volume to about 85% by volume of the composite, said composite having a porosity of less than about 5% by volume of said composite, said ceramic member being selected from the group consisting of boron carbide, hafnium carbide, hafnium nitride, niobium carbide, niobium nitride, silicon carbide, tantalum carbide, tantalum nitride, titanium carbide, titanium nitride, vanadium carbide, vanadium nitride, zirconium carbide and zirconium nitride, said fluoride-containing member being selected from the group consisting of barium fluoride, calcium fluoride, magnesium fluoride, strontium fluoride, cerium fluoride, dysprosium fluoride, gadolinium fluoride, lanthanum fluoride, samarium fluoride, yttrium fluoride and a mixture of at least about 10% by volume of said fluoride and a metal oxide selected from the group consisting of magnesium oxide, calcium oxide, alumina and a mixture of said oxide.

A polycrystalline composite comprised of silicon carbide in an amount ranging from about 5% by volume to about 70% by volume of the composite and a fluoride-containing member in amount from about 30% by volume to about 95% by volume of the composite, said composite having a porosity of less than about 5% by volume of said composite, said fluoride-containing member being selected from the group consisting of barium fluoride, calcium fluoride, magnesium fluoride, strontium fluoride, cerium fluoride, dysprosium fluoride, gadolinium fluoride, lanthanum fluoride, samarium fluoride and yttrium fluoride.

A polycrystalline composite comprised of silicon nitride in an amount ranging from about 5% by volume to about 70% by volume of the composite and a fluoride-containing member ranging in amount from about 30% by volume to about 95% by volume of the composite, said composite having a porosity of less than about 10% by volume of said composite, said silicon nitride being particulate in form and/or in the form of filaments, said fluoride-containing member being selected from the group consisting of barium fluoride, calcium fluoride, magnesium fluoride, strontium fluoride, cerium fluoride, dysprosium fluoride, gadolinium fluoride, lanthanum fluoride, samarium fluoride, yttrium fluoride and a mixture of at least about 10% by volume of said fluoride and a metal oxide wherein said mixture of said fluoride and metal oxide has a liquidus temperature ranging from above 1000.degree. C. to below about 1500.degree. C.