Chemical vapor infiltration method for densifying porous substrates having a central passage

A chemical vapor infiltration method for densifying at least one porous substrate having a central passage, the method comprising the steps of:

• placing one or more porous substrates inside an enclosure to define within the enclosure an inside volume formed essentially by the central passage of the substrate or the central passages of a plurality of substrates in alignment, and an outer volume formed essentially by the outside of the substrate(s);
• providing at least one leakage passage putting said volumes into communication with each other other than through the substrate(s);
• admitting into the enclosure a gas containing at least one gaseous precursor of a matrix material to be deposited within the pores of the substrate(s);
• channeling the gas towards a first one of the inside and outer volumes, said first volume being closed at an end opposite from the end where the gas is admitted;
• and
• carrying out the densification of said substrate(s) by causing the gas to flow inside the enclosure from the first volume to the other or second of the inside and outer volumes by diffusing through the pores of the substrate(s) and by passing through the or each leakage passage, and by extracting residual gas from the enclosure from the second volume, in which:
• a maximum acceptable threshold value inside the first volume for the pressure of the gas or for the partial pressure of the precursor contained in the gas is defined;
• and
• the total leakage section of the leakage passage(s) is given a value lying between a minimum value such that, for a given gas flow rate admitted into the enclosure, the maximum pressure value is not exceeded before the end of the densification process, and a maximum value such that a pressure difference is established between the first volume and the second volume as from the beginning of the densification process.

A chemical vapor infiltration method for densifying at least one porous substrate having a central passage, the method comprising the steps of:

• placing one or more porous substrates inside an enclosure to define within the enclosure an inside volume formed essentially by the central passage of the substrate or the central passages of a plurality of substrates in alignment and an outer volume formed essentially by the outside of the substrate(s),
• providing at least one leakage passage putting said volumes into communication with each other other than through the substrate(s);
• admitting into the enclosure a gas containing at least One gaseous precursor of a matrix material to be deposited within the pores of the substrate(s);
• channeling the gas towards a first one of the inside and outer volumes, said first volume being closed at an end opposite from the end where the gas is admitted;
• and
• carrying out the densification of said substrate(s) by causing the gas to flow inside the enclosure from the first volume to the other or second of the inside and outer volumes by diffusing through the pores of the substrate(s) and by passing through the or each leakage passage, and by extracting residual gas from the enclosure from the second volume, in which;
• a maximum acceptable threshold value inside the first volume for the pressure of the gas or for the partial pressure of the precursor contained in the gas is defined;
• and
• the total leakage section of the leakage passage(s) is given a value lying between a minimum value such that the maximum pressure value is not exceeded before the end of the densification process, and a maximum value such that a pressure difference is established between the first volume and the second volume as from the beginning of the densification process, the minimum value of the total leakage section being such that the pressure difference between the first and the second volumes at the beginning of the densification process is not greater than 85% of the value of the pressure difference obtained in the absence of any leakage passage.

A chemical vapor infiltration method for densifying at least one porous substrate having a central passage, the method comprising the steps of:

• placing a plurality of porous substrates inside an enclosure to form at least one stack of substrates with the central passages of the substrates being in alignment, thereby defining within the enclosure an inside volume formed essentially by the inside of the stack(s) and an outer volume formed by the outside of the stack(s), said at least one stack also including spacers each adjacent to one substrate;
• providing at least one of said spacers with at least one radial passage forming a leakage passage putting said volumes into communication with each other other than through the substrate(s);
• admitting into the enclosure a gas containing at least one gaseous precursor of a matrix material to be deposited within the pores of the substrate(s);
• channeling the gas towards a first one of the inside and outer volumes, said first volume being closed at an end opposite from the end where the gas is admitted;
• carrying out the densification of said substrate(s) by causing the gas to flow inside the enclosure from the first volume to the other or second of the inside and outer volumes by diffusing through the pores of the substrate(s) and by passing through the or each leakage passage, and by extracting residual gas from the enclosure from the second volume, in which:
• a maximum acceptable threshold value inside the first volume for the pressure of the gas or for the partial pressure of the precursor contained in the gas is defined;
• and
• the total leakage section of the leakage passage(s) is given a value lying between a minimum value such that the maximum pressure value is not exceeded before the end of the densification process, and a maximum value such that a pressure difference is established between the first volume and the second volume as from the beginning of the densification process.