RU2471750C1 - Method of making articles from carbon-silicon carbide material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to structural materials operating in conditions of high thermal load and oxidative medium and can be used in chemical, petrochemical and chemical-metallurgical industries, as well as aircraft engineering to make articles and structural components exposed to aggressive media, particularly nozzles, crucibles, furnace components, high-temperature turbines and aircraft exposed to considerable mechanical load during operation. A workpiece made of porous graphitised carbon material is heated in the closed volume of a reactor in an inert atmosphere or a vacuum in silicon vapour to temperature of 1500-1550°C, or 1550-1600°C, or 1600-1650°C, or 1650-1700°C at pressure of 1-36 mm Hg, after which the workpiece is held in one of said temperature and pressure intervals for 1-3 hours and then cooled to 1300-1400°C. Said operations are preferably repeated up to 3 times. The workpiece is then heated to 1750-1900°C, held in that temperature interval for 1-3 hours and then finally cooled.

EFFECT: high degree and uniformity of siliconisation and high reproducibility of results from process to process.

3 cl, 5 ex, 2 tbl

Description

The invention relates to the field of structural materials operating in conditions of high thermal loading and an oxidizing environment, and can be used in the chemical, petrochemical and chemical-metallurgical industries, as well as in aircraft to create products and structural elements exposed to aggressive environments, in particular nozzles, crucibles, parts of thermal units, high-temperature turbines and aircraft experiencing significant mechanical stress during operation.

A known method of manufacturing products from carbon-carbide-silicon material (UKKM), including the manufacture of a workpiece from a porous carbon-graphite material and its silicification by the liquid-phase method [Tarabanov A.S. and others. Siliconized graphite, M .: Metallurgy, 1977, p.208].

The disadvantage of this method is the complexity of the manufacturing technology of products from UKKM due to the need to heat them from 1300 to 1650 ° C at a speed of at least 600 degrees / hour for the fast transfer of the silicon melt to a low-viscosity state. Otherwise (at a low heating rate), a viscous silicon melt flows into the surface pores of the workpiece material and is carburized, which leads to a loss of its ability to flow during subsequent heating and, as a result, to surface silicification.

The closest to the expected technical essence and the achieved effect is a method of manufacturing products from UKKM, including the manufacture of a workpiece from porous carbon-graphite material, heating it in a closed volume in an inert atmosphere or vacuum in silicon vapor to 1700-1900 ° C, followed by exposure in the specified interval temperatures for 1-3 hours and cooling [patent RU No. 1834839, cl. C01B 31/02, 1993]. This method is adopted as a prototype.

The method allows to simplify the manufacturing technology of products from UKKM due to the fact that there is no need to conduct heating from 1300 to 1650 ° C at a high speed (heating can be carried out at a speed of 100-300 degrees / hour). In addition, the method allows to obtain UKKM with significantly less open porosity than the analogue method.

Signs of the prototype, coinciding with the essential features of the proposed method is the manufacture of a workpiece from porous carbon-graphite material; heating the workpiece in a closed reactor volume in an inert atmosphere or vacuum in silicon vapor to 1700-1900 ° C, followed by exposure in the indicated temperature range for 1-3 hours; cooling.

The disadvantage of this method, taken as a prototype, is the insufficient and / or unequal height and perimeter of the workpiece, the degree of silicification, as well as poor reproducibility of the results from process to process, including the composition of the CCM. This is an experimentally established fact. This is apparently due to the low mass transfer rate of silicon vapors to the surface of the siliconized part, as well as to the negative influence of gas-dynamic flows.

The objective of the invention is to increase the degree and uniformity of silicification, as well as increasing the reproducibility of the results from process to process.

The problem was solved due to the fact that in the known method of manufacturing products from UKKM, including the manufacture of a workpiece from porous carbon-graphite material, heating it in a closed volume of the reactor in an inert atmosphere or vacuum in silicon vapor to 1700-1900 ° C, followed by exposure to the specified the temperature range for 1-3 hours and cooling, heating the workpiece to 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C are carried out at a pressure of 1-36 mm. Hg followed by exposure in one of the indicated temperature and pressure ranges for 1-3 hours and cooling to 1300-1400 ° C, after which the workpiece is heated to 1750-1900 ° C, kept in the specified temperature range for 1-3 hours and finally cool.

It is advisable to cool the workpiece to 1300-1400 ° C at a speed of 100-200 degrees / hour, repeat up to 3 times the heating and holding the workpiece at 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C followed by cooling to 1300-1400 ° C.

The features of the proposed technical solution, distinctive from the prototype: heating the workpiece to 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C lead at a pressure of 1-36 mm. Hg; holding the workpiece in one of the indicated temperature and pressure ranges for 1-3 hours; cooling the workpiece to 1300-1400 ° C; heating the workpiece to 1750-1900 ° C; holding the workpiece in the specified temperature range for 1-3 hours; final cooling; cooling the workpiece to 1300-1400 ° C is carried out at a speed of 100-200 degrees / hour; heating and holding the workpiece at 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C, followed by cooling to 1300-1400 ° C, is repeated up to 3 times.

Keeping the workpiece heated to 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C at a pressure of 1-36 mm Hg with subsequent exposure in the indicated temperature and pressure ranges for 1-3 hours and cooling to 1300-1400 ° C, even before the workpiece is held at 1700-1900 ° C, most of the silicon can be introduced into it (this is an experimentally established fact by us).

The cooling of the workpiece from 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C to 1300-1400 ° C with a speed of 100-200 degrees / hour provides a more complete filling of the pores of the material silicon.

Repeating up to 3 times the heating and aging of the workpiece at 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C for 1-3 hours, followed by cooling to 1300-1400 ° C provides a more complete and uniform filling and pore filling of the material with silicon, which is especially important for bulky workpieces.

Subsequent heating and exposure at 1700-1900 ° C for 1-3 hours ensures the transfer of silicon, which has entered the pores of the material, into silicon carbide.

In this case, the formation of SiC is accompanied by the occurrence of a silicon deficit in the pores of the material, and where the SiC layer has not yet reached the maximum thickness (for diffusion of C and Si through it), Si vapor diffuses from the reactor volume, and where it has already reached, it does not diffuse.

Heating the workpiece at a pressure of 1-36 mm Hg up to a temperature of more than 1700 ° C is impractical because a sufficiently large amount of silicon enters the pores of the material at lower temperatures, and the process is unreasonably extended. Moreover, if the occurrence of the first portions of silicon coincides with a temperature of more than 1700 ° C, when silicon has a relatively high chemical activity, this can lead to a decrease in the physicomechanical characteristics of CCFM due to the partial carbidization of carbon fibers.

The final cooling of the workpiece ensures the completion of the manufacturing process of the product from UKKM.

In the new set of essential features the object of the invention has a new property: the ability to introduce most of the silicon into the pores of the carbon-graphite material even before the exposure stage at 1750-1900 ° C, and at the aging stage to ensure its additional introduction in those areas where it was insufficient transferring silicon carbide into silicon carbide and bringing its content to the limit value, as a result of which the degree of siliconization of carbon-graphite material is aligned along the height and perimeter of the workpiece. The new property allows to increase the degree and uniformity of silicification, as well as to increase the reproducibility of the results from process to process. The method is as follows.

One of the known methods is made of a blank of porous carbon-graphite material. Then the workpiece is heated in a closed reactor volume in silicon vapor to a temperature of 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C at a pressure of 1-36 mm RT.article After that, the workpiece is kept in one of the above temperature and pressure ranges for 1-3 hours. During this period, silicon evaporates from crucibles located around the workpiece. Silicon vapor fills the volume of the reactor, and then diffuses in the volume of the reactor to the surface of the workpiece, and then into the pores of the material. But this happens at a low speed. Then the workpiece is cooled to a temperature of 1300-1400 ° C at a pressure of 1-36 mm RT.article, while the most optimal is the cooling rate in the range of 100-200 deg / hour.

During the exposure of the workpiece at temperatures of 1500-1550 ° C, 1550-1600 ° C, 1600-1650 ° C or 1650-1700 ° C and cooling to 1300-1400 ° C, for reasons known to us (namely, due to the condensation of silicon vapor on the surface and / or directly in the pores of the CCM), the transfer of silicon vapors to the pores of the material is intensified, where silicon is carbidized, resulting in its deficiency. Therefore, where silicon deficiency occurs, silicon vapors diffuse from the reactor volume. Where silicon deficiency does not occur (and this happens when the thickness of the SiC layer reaches the maximum thickness for diffusion through it of C and Si), silicon vapors do not diffuse. This leads to the alignment of the silicon content along the height and perimeter of the workpieces from UKKM.

Then the preform is heated to 1750-1900 ° C and kept in the indicated temperature range for 1-3 hours. During this period, the process of silicon carbidization and the alignment of its content in the workpiece from UKKM are completed. After that, the workpiece is finally cooled and removed from the reactor.

The following are examples of a specific implementation of the method of manufacturing parts from UKKM.

Example 1

The part was made in the form of a plate measuring 690 × 440 × 4 mm. For this, a carbon-plastic preform based on a high-modulus carbon fabric of the UT-900 brand and a phenol-formaldehyde binder of the BZ brand was carbonized in a retort furnace in a nitrogen atmosphere at a final temperature of 850 ° C. Then, the carbonized carbon fiber obtained with a density of 1.1-1.3 g / cm ^{3 was then} saturated with pyrocarbon by a vacuum isothermal method at a temperature of 900-1000 ° C to a density of 1.45-1.53 g / cm ³ and an open porosity of 6-12 % Then the plate and crucibles with silicon were placed in a closed volume of the reactor. In a specific case, a carbon-graphite plate with a density of 1.5 g / cm ³ and an open porosity of 11.7% was installed. The installation was evacuated to 18 mm Hg. Heating to 1500-1550 ° C was carried out at a speed of 150-200 deg / h. Then spent holding at 1500-1550 ° C for 2 hours. After that, the charge was cooled to 1300 ° C at a rate of ≈150 deg / h. Then the charge was heated to 1800-1850 ° C at a speed of 150-200 deg / h and kept at 1800-1850 ° C for 2 hours. After that, the cage was finally cooled to 70 ° C and removed from the installation.

The result was a plate made of UKKM with a density of 1.84 g / cm ³ and an open porosity of 8.0%. The total silicon content in UKKM amounted to 18.5 wt.%.

Example 2

A large-sized part ⌀ 1500 mm and a height of 2000 mm was made in the form of a thin-walled shell. The source material of the part had a density of 1.48 g / cm ³ and an open porosity of 9.8%. Siliconization was carried out analogously to example 1 with the only difference being that the pressure in the reactor was set at 3 mm Hg.

As a result, a part was obtained from UKKM with a density dispersion along the height and perimeter of the part in the range of 1.74-1.92 g / cm ³ .

Example 3

Analogously to example 2 with the only difference that the operations of heating and aging at a temperature of 1500-1550 ° C and cooling to 1300 ° C were carried out 3 times.

As a result, we obtained a part from UKKM with a significantly smaller density spread along the height and perimeter of the part, namely: within 1.83-1.92 g / cm ³ .

Table 1 shows a more concise summary of examples 1-7 of the manufacture of products from UKKM the proposed method. The technological parameters of the siliconization process in examples 1-5 correspond to the claimed ranges of their values, in examples 6, 7, respectively, the values of heating and holding temperatures and the pressure value above the upper limit. Example 8 corresponds to the prototype method.

In evidence of the effectiveness of the additional holding stage at a temperature of 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C and a pressure of 1-36 mm Hg followed by cooling to 1300-1400 ° C in table 2 shows examples 1-4 of a specific implementation of the method of manufacturing products from UKKM with an indication of the basic properties of the intermediate and final UKKM.

Below, in more detail, only Examples 1, 2 are given. Examples 1-4 of Table 2 correspond to Examples 4-7 of Table 1.

Example 1, table 2 (in table 1 corresponds to example 4).

The part was made in the form of a plate with dimensions of 660 × 440 × 4 mm. A plate made of carbon-graphite material with a density of 1.5 g / cm ³ and an open porosity of 11.7% was installed for silicification. The silicification process was carried out analogously to example 1, table 1, but did not bring it to the end, namely: after exposure at 1550-1600 ° C, without heating and aging at 1800-1850 ° C, it was finally cooled to 70 ° C; while cooling to 1300 ° C was carried out at a rate of ≈150 deg / h.

After removing the preform, studies were performed. As a result of the studies, it was found that the UKKM had a density of 1.81 g / cm ³ and an open porosity of 3.7%. The content of total silicon in the UKCM was 18.0 wt%, which is evidence that a significant part of the silicon entered the material even before the stage of exposure at a temperature of 1800-1850 ° C.

After conducting studies, the plate was set to a mode that complements the one already carried out, namely: the plate was heated in silicon vapor from room temperature to a temperature of 1800-1850 ° C at a speed of 150-200 deg / h at a pressure of 18 mm Hg. followed by exposure in the indicated temperature range for 1 hour and cooling to 70 ° C.

As a result, a CCM with a density of 1.86 g / cm ³ and an open porosity of 8.8% was obtained. The content of total silicon in UKKM amounted to 20.1 wt.%. From a comparison of the total silicon content in the UKCM after the condensation of Si vapor directly in the pores of the material and after the final treatment, it follows that most of the silicon entered at the first stage.

Example 2, table 2 (in table 1 corresponds to example 5).

Analogously to example 1 of table 2 with the only difference that the exposure was carried out at 1600-1650 ° C. As a result, already at this stage, i.e. before exposure at 1800-1850 ° C, they obtained a UKKM with a density of 1.78 g / cm ³ and an open porosity of 3.4%. In this case, the content of total silicon in the UKCM was 18.5 wt.%, Which is evidence that a significant part of the silicon entered the material even before the exposure stage at a temperature of 1800-1850 ° C.

After conducting studies, the plate was set to a mode that complements the previously conducted mode, namely: the plate was heated in silicon vapor from 20 ° C to a temperature of 1800-1850 ° C at a pressure of 18 mm Hg. at a speed of 150-200 degrees / hour, followed by exposure in the indicated temperature range for 1 hour. After that, the cage was cooled to 70 ° C and the plate was removed.

The result was a UKKM with a density of 1.88 g / cm ³ and an open porosity of 9.2%. The content of total silicon in UKKM amounted to 20.2 wt.%. From a comparison of the total silicon content in the UKCM after the condensation of silicon vapors directly in the pores of the material and after the final processing, it again follows that most of the silicon entered at the first stage.

From the analysis of tables 1 and 2, we can draw the following conclusions:

1. Products made from UKKM by the proposed method in accordance with the claimed modes (examples No. 1-5) have a fairly high degree and uniformity of silicification.

2. Products made from UKKM by the proposed method, but not in accordance with the claimed modes, have an insufficient degree and uniformity of silicification and a lower tensile strength.

3. Products made from UKKM by a known prototype method have even lower rates in terms of degree and uniformity of silicification.

Statistical processing of the results of silicification in retorts of ⌀700 × h1600 mm and ⌀1700 × h2400 mm by the proposed method showed that satisfactory results in the degree and uniformity of silicification were obtained in 72 and 40% of cases, and in the prototype method in 43 and 21% of cases, respectively . This indicates a higher degree of reproducibility of obtaining satisfactory results of silicification of the proposed method in comparison with the method of the prototype.

Table 1 No. p / p Sizes of blanks, mm Main characteristics of carbon-graphite material Siliconization process parameters Main characteristics of UKKM Note γ, g / cm ³ OP,% γ, g / cm ³ OP,% The total silicon content in wt.% one 2 3 four 5 6 7 8 9 one 690 × 440 × 4 1,5 11.7 Heating and holding at 1500-1550 ° C and a pressure of 18 mm Hg within 120 minutes Cooling to 1300 ° C at a speed of ~ 150 deg / h. Heating and holding at 1800-1850 ° C for 60 minutes 1.84 8.0 18.5 Sufficiently uniform siliconization 2 Thin-walled shell ⌀1500 × h2000 mm 1.48 9.8 Similar to 1st example. The difference is that they set the pressure in the reactor to 3 mm Hg. 1.74-1.92 7.6-12.8 14.9-22.9 Not sufficiently high silicon uniformity 3 - // - 1.49 8.6 Similarly to the 2nd example. The difference is that heating and holding at 1500-1550 ° C and cooling to 1300 ° C were repeated 3 times 1.83-1.92 8.0-10.7 18.6-22.4 Sufficiently uniform siliconization four 690 × 440 × 4 1,5 11.7 Heating and holding at 1550-1600 ° C and a pressure of 18 mm Hg within 120 minutes Cooling to 1300 ° C at a speed of ~ 150 deg / h. Heating and holding at 1800-1850 ° C for 60 minutes 2.03 8.8 20.1 Corresponds to example 1 in table 2 5 - // - - // - - // - Heating and holding at 1600-1650 ° C and a pressure of 18 mm Hg within 90 minutes Cooling to 1300 ° C at a speed of ~ 150 deg / h. Heating and holding at 1800-1850 ° C for 60 minutes 1.88 9.2 20,2 Corresponds to example 2 in table 2 6 - // - - // - - // - Heating and holding at 1700-1750 ° C and a pressure of 18 mm Hg within 60 minutes Cooling to 1300 ° C at a speed of ~ 150 deg / h. Heating and holding at 1800-1850 ° C for 60 minutes 1.7-1.83 9.3-12.9 11.8-18.0 Corresponds to example 3 in table 2 7 - // - - // - - // - Heating and holding at 1500-1550 ° C and a pressure of 100 mm Hg within 60 minutes Cooling to 1300 ° C at a speed of ~ 150 deg / h. Heating and holding at 1800-1850 ° C for 60 min. 1.7-1.83 9.3-12.9 11.8-18.0 Corresponds to example 4 in table 2 8 - // - 1.48 7.9 Heating and aging in silicon vapors at 1800-1850 ° C and a pressure of 3 mm Hg within 120 minutes Cooling to 70 ° C 1.62-1.87 9.1-12.9 8.6-20.8 High Silicon Irregularity

Claims (3)

1. A method of manufacturing products from carbon-carbide-silicon material, including the manufacture of a workpiece from porous carbon-graphite material, heating it in a closed reactor volume in an inert atmosphere or vacuum in silicon vapor to 1700-1900 ° C, followed by exposure in the specified temperature range for 1- 3 hours and cooling, characterized in that the preform is heated to 1500-1550 ° C, or 1550-1600 ° C, or 1600-1650 ° C, or 1650-1700 ° C, at a pressure of 1-36 mm Hg. followed by exposure in one of the indicated temperature and pressure ranges for 1-3 hours and cooling to 1300-1400 ° C, after which the workpiece is heated to 1750-1900 ° C, kept in the specified temperature range for 1-3 hours and finally cool. 2. The method according to claim 1, characterized in that the cooling of the workpiece to 1300-1400 ° C is carried out at a speed of 100-200 deg / h. 3. The method according to any one of claims 1, 2, characterized in that the heating and holding the workpiece at 1500-1550 ° C, 1550-1600 ° C, 1600-1650 ° C or 1650-1700 ° C, followed by cooling to 1300- 1400 ° C is repeated up to 3 times.