CVI matrix densification process
Disclosed herein is a chemical vapor infiltration method including flowing ceramic precursors through a preform and depositing a matrix material on the preform at a first gas infiltration pressure, increasing the gas filtration pressure to a second gas infiltration pressure, and lowering the gas infiltration pressure to a third gas infiltration pressure which is intermediate to the first and second gas infiltration pressures.
1. A chemical vapor infiltration method comprising:
flowing ceramic precursors through a preform in a reactor and depositing a matrix material on the preform at a first gas infiltration pressure of the reactor,
increasing the gas filtration pressure to a second gas infiltration pressure, and
lowering the gas infiltration pressure to a third gas infiltration pressure which is intermediate to the first and second gas infiltration pressures;
wherein the first pressure is less than or equal to 1 torr, and wherein the first pressure is 1 to 20% of the second pressure;
wherein the second pressure is greater than 1 torr, and wherein the second pressure is maintained until infiltration gas diffusion rate rather than deposition rate controls matrix densification rate; and
wherein the third pressure is 25 to 75% of the second pressure, and wherein the third pressure maintains matrix densification under reaction control rather than diffusion control.
2. The method of claim 1 , wherein the first pressure is maintained at the first pressure for one minute to 60 minutes.
3. The method of claim 1 , wherein the first pressure is 0.01 torr to 1 torr.
4. The method of claim 1 , wherein the second pressure is greater than 1 torr to 100 torr.
5. The method of claim 1 , further comprising a fourth pressure intermediate to the first and third pressures.
6. The method of claim 1 , wherein the increase in gas infiltration pressure from the first gas infiltration pressure to the second gas infiltration pressure is based on a reduction in pore size, and the decrease in gas infiltration pressure from the second gas infiltration pressure to the third gas infiltration pressure is based on a decrease in a rate of weight increase.
7. The method of claim 1 , wherein the preform comprises Al 2 O 3 —SiO 2 , SiC, silicon dioxide (SiO 2 ), aluminum silicate, aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ), zirconium silicate, silicon nitride, boron nitride (BN), carbon (C), and combinations thereof.
8. The method of claim 1 , wherein the matrix comprises metal oxides, borides, carbides, nitrides, silicides, and mixtures and combinations thereof.
9. The method of claim 8 , wherein the matrix comprises silicon carbide (SiC), silicon oxide (SiO 2 ), boron nitride (BN), boron carbide (B 4 C), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), zirconium boride (ZrB 2 ), zinc oxide (ZnO 2 ) molybdenum disulfide (MoS 2 ), silicon nitride (Si 3 N 4 ), and combinations thereof.
10. The method of claim 1 , further comprising modifying the temperature, precursor flow rate or both.
11. A chemical vapor infiltration method comprising:
flowing SiC ceramic precursors through a SiC preform in a reactor and depositing a SiC matrix material on the preform at a first gas infiltration pressure of the reactor,
increasing the gas filtration pressure to a second gas infiltration pressure, and
lowering the gas infiltration pressure to a third gas infiltration pressure which is intermediate to the first and second gas infiltration pressures;
wherein the first pressure is less than or equal to 1 torr, and wherein the first pressure is 1 to 20% of the second pressure;
wherein the second pressure is greater than 1 torr, and wherein the second pressure is maintained until infiltration gas diffusion rate rather than deposition rate controls matrix densification rate; and
wherein the third pressure is 25 to 75% of the second pressure, and wherein the third pressure maintains matrix densification under reaction control rather than diffusion control.
12. The method of claim 11 , wherein the first pressure is 0.01 torr to 1 torr.
13. The method of claim 11 , wherein the second pressure is greater than 1 torr to 100 torr.
14. The method of claim 11 , wherein the increase in gas infiltration pressure from the first gas infiltration pressure to the second gas infiltration pressure is based on a reduction in pore size, and the decrease in gas infiltration pressure from the second gas infiltration pressure to the third gas infiltration pressure is based on a decrease in a rate of weight increase.
15. The method of claim 11 , wherein the first pressure is maintained at the first pressure for one minute to 60 minutes.
16. The method of claim 11 , further comprising a fourth pressure intermediate to the first and third pressures.