Method of densifying porous billets

A continuous chemical vapor deposition process for the densification of a porous preform structure comprising a porous substrate body having voids extending inwardly from the surfaces thereof which render said body porous, comprising the steps of:

• (a) providing a reaction vessel for carbon-precursor liquid(s) which are heat-decomposable at elevated temperatures to vapor-deposit coatings on the surfaces of said substrate body to fill said voids and densify said preform structure;
• (b) supplying said reaction vessel with a first said coating-precursor liquid which is heat-decomposable to vapor-deposit a carbon coating on the surfaces of said porous substrate body;
• (c) inserting a said porous substrate body within said reaction vessel to submerge said body in said liquid;
• (d) heating the fibrous porous substrate body submerged within the carbon-precursor liquid to an elevated temperature sufficient to decompose the precursor liquid and cause the vapor deposition of a carbon layer on the surfaces of said substrate body, and
• (e) continuing said heating while the preform is submerged in said liquid to cause the vapor deposit to accumulate on said porous substrate body, as a carbon layer;
• (f) replacing the first liquid within said reaction vessel with a second coating-precursor liquid which is heat-decomposable at elevated temperatures to a vapor and deposits a ceramic or organometallic layer over the carbon layer on said porous substrate body;
• (g) heating the carbon-coated porous substrate body submerged within the second coating-precursor liquid to an elevated temperature sufficient to decompose said precursor liquid and cause the vapor deposition of a ceramic or organometallic layer over the carbon layer on the surfaces of said substrate body, and
• (h) continuing said heating while the substrate body remains submerged in said second coating--precursor liquid to cause the vapor deposit to accumulate on said body, fill said voids and form a densified preform structure enclosed within said ceramic or organometallic material.