RU2592587C1 - METHOD OF PRODUCING HEAT-SHIELDING LAYERED COMPOSITE MATERIAL OF Zrm(O-B-C)nSYSTEM - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of composite materials, mainly for structural purposes, and can be used for making heat-shielding laminar composite articles, intended, for example, for efficient heat protection of aerospace aircraft and their power systems. Method of producing heat-shielding layered composite material of Zr_m(O-B-C)_n system involves preparation of powders of at least two selected compounds of said system: ZrO₂, ZrB₂ or ZrC, moulding workpieces therefrom and layering workpieces into a graphite mould, hot pressing. During layering an intermediate layer of powder mixture of selected compounds of said system is placed between said workpieces, volume fraction in mixture of which is determined from formula:

, where: α₁, α₂ are CTE of selected compounds, V₁, V₂ are volume fractions of selected compounds in mixture, wherein thickness of intermediate layer is calculated by formula: ΔH=(α₁h₁+α₂h₂)ΔT (2), where: ΔH is thickness of intermediate layer, α₁, α₂ are CTE of selected compounds, h₁, h₂ are thickness of workpieces, ΔT is temperature difference, given in mode of hot pressing of material. Powders of selected compounds are prepared by treatment in ball mill in gasoline for 80-100 hours, then dried powders are strained through a sieve. Workpieces are moulded by pressing in mould at pressure of 100-200 MPa. Hot pressing is performed at 1,400-1,700 °C, pressure of 10-20 MPa for 20-30 minutes in nitrogen medium.

EFFECT: avoiding slip cracks formed during cooling in process of producing heat-shielding layered composite material, as well as improved mechanical properties.

4 cl, 4 ex

Description

The invention relates to the production of composite materials (KM), mainly for structural purposes, and can be used for the manufacture of heat-protective layered composite products intended, for example, for the effective thermal protection of aerospace aircraft and their energy systems.

A known substrate with a ceramic coating that creates a thermal barrier, with two ceramic layers (RU 2509177, C23C 28/04, B32B 3/26, B32B 18/00, publ. 03/10/2014). The substrate with a thermal barrier coating comprises said substrate, said ceramic coating made of two ceramic layers, said coating having different thicknesses at different locations on said substrate. There is no metal layer between the inner ceramic layer and the outer ceramic layer, said coating on said substrate having a first region and a second region. The outer layer is thicker, in particular at least twice as thick, in the second region than the ceramic layer in the first region on said substrate. The technical result consists in creating a thermal barrier with high resistance to thermal and mechanical stresses.

The disadvantage of this invention is that in the case of a significant difference in the CTE of the materials of the layers when they are cooled from the production temperature at the interface, a voltage exceeds the strength of the material.

A known method of producing multilayer ceramic products from composite material (RU 2112762, C04B 35/596, C04B 35/58, B32B 18/00, publ. 06/10/1998). The method consists in preparing a ceramic mixture of at least two compositions containing a composition of silicon nitride - yttrium oxide or silicon nitride - magnesium oxide and boron nitride with different ratios of components, pre-compacted on a mechanical press in metal molds into briquettes from a charge from a composition based on silicon nitride with a stepwise change in the content of boron nitride to 50 wt. %, the number of briquettes and the stacking sequence are determined by a specific range of properties, and hot pressing is carried out at temperatures of 1550-1700 ° C and a pressure of 10-20 MPa for 2 to 3 hours in a nitrogen environment (prototype).

The disadvantage of this invention is that when sintering different layers of material have different shrinkage coefficients, which leads to the appearance of discontinuities at the interface.

The objective of the invention is to develop a method for producing a heat-protective laminated composite material of the system Zr _m (OBC) _n .

The technical result of the invention is the elimination of delamination cracks formed during cooling in the process of obtaining a heat-protective layered composite material.

Also an additional technical result of the invention is that the obtained heat-shielding laminated composite material of the Zr _m (OB-C) _{n system} has high mechanical properties.

The specified technical result is achieved in that the method for producing a heat-protective layered composite material of the Zr _m (OBC) _{n system} includes the preparation of powders of at least two selected compounds of the specified system, the formation of blanks from them and layering of the blanks in a graphite hot mold pressing, while layering between the blanks, an intermediate layer of a powder mixture of selected compounds of the specified system is placed, the volume fractions of which in the mixture are determined from the formula:

, где:

where:

α ₁ , α ₂ - CTE of the selected compounds,

V ₁ , V ₂ - volume fraction of selected compounds in the mixture,

while the thickness of the intermediate layer is calculated by the formula:

, где:

where:

ΔН is the thickness of the intermediate layer,

α ₁ , α ₂ - CTE of the selected compounds,

h ₁ , h ₂ - the thickness of the workpieces,

ΔT is the temperature difference specified by the hot pressing mode of the material.

The powders of the selected compounds are prepared by processing in a ball mill in gasoline for 80-100 hours, then the dried powders are wiped through a sieve. The blanks are formed by compression molding in a mold at a pressure of 100-200 MPa. Hot pressing is carried out at a temperature of 1400-1700 ° C, a pressure of 10-20 MPa for 20-30 minutes in a nitrogen environment.

There are various methods for producing multilayer structural heat-insulating products consisting of dense and porous layers. Known techniques cannot be called effective due to a number of disadvantages. The main one is that the product is actually molded and fired several times. When molding, for example, two-layer multi-density products by injection molding, followed by drying and firing between the layers, a sharp boundary is created on which stresses arising due to differences in shrinkage, creep and coefficient of thermal expansion of the layers are concentrated. Therefore, the authors propose to produce compaction and connection of the layers through the intermediate layer in one technological process.

It is known that hot pressing has significant advantages for the production of multilayer ceramic composites due to their significant compaction. The advantages also include a higher dimensional accuracy of the parts to be manufactured, the possibility of using various feedstocks, and obtaining a unique combination of properties in the manufacture of multilayer composite materials. Hot pressing allows the use of powders with a wider range of characteristics, while compaction occurs at a lower temperature.

In the present invention, the components of the composite material can be preformed in the form of blanks, for example, by pressing at a pressure of 100-200 MPa.

Pressed billets provide the possibility of layering them in a graphite mold, preventing mechanical mixing of powders of different initial components at the initial stage of hot pressed.

The heat-shielding laminated composite material of the Zr _m (OBC) _{n system is} prepared as follows.

The powders of at least two selected compounds of the Zr _m (OBC) _{n system} , taken in the required amount, are treated individually in a ball mill in gasoline for 80-100 hours. The dried powders are wiped through a sieve. Then, from the prepared powders, at least two preforms of a given shape are formed by pressing in a metal mold with a thickness of respectively h ₁ , h ₂ .

Next, a powder mixture of the intermediate layer is prepared from two selected compounds of the Zr _m (OBC) _{n system} , calculating their volume fractions (V ₁ , V ₂ ) in the powder mixture according to formula (1) based on the CTE of the selected compounds (α ₁ , α ₂ ). Then calculate the thickness of the intermediate layer of the powder mixture (ΔH) according to the formula (2) based on the values of:

- thicknesses of two blanks (h ₁ , h ₂ ),

- CTE of the selected compounds (α ₁ , α ₂ ),

- ΔT is the temperature difference specified by the hot pressing mode of the material.

The resulting at least two preforms are stacked on top of each other in a graphite mold and an intermediate layer of the calculated thickness (ΔH) from a powder mixture of two selected compounds of the Zr _m (OBC) _n system is placed between them. Next, hot pressing is carried out at a temperature of 1400-1700 ° C and a pressure of 10-20 MPa for 20-30 minutes in a protective nitrogen atmosphere.

Case Studies

As the starting components use powders:

- zirconium dioxide TU2320-001-07622928-96,

- zirconium diboride obtained by the borothermic method,

- zirconium carbide obtained by carbidization of zirconium oxide.

Example 1

From the prepared zirconia and zirconium carbide powders, rectangular preforms 1 and 2 are formed by compression, respectively, in a metal mold at a pressure of 200 MPa, for example, 5 mm and 10 mm thick.

Then, an intermediate layer powder mixture is prepared from zirconia and zirconium carbide powders by calculating their volume fractions in the powder mixture according to formula (1) based on their KTP. We obtain their volume fractions in the powder mixture, respectively, 58% and 42%.

Next, the thickness of the intermediate layer is calculated by the formula (2) based on the values of the thicknesses of the workpieces 1 and 2, KTR of zirconium dioxide and zirconium carbide, respectively equal to 10 × 10 ^-6 K ^-1 and 7 × 10 ^-6 K ^-1 , ΔT = 1600 ° C - set by the mode of hot pressing of the material. We get the estimated thickness of the intermediate layer, equal to 0.20 mm

The obtained preforms of zirconium diboride and zirconium carbide are stacked on top of each other in a graphite mold and an intermediate layer of a powder mixture of calculated thickness is placed between them, then hot pressing is carried out at a temperature of 1600 ° C and a pressure of 10 MPa for 25 minutes in a protective nitrogen atmosphere.

Example 2

From prepared powders of zirconia and zirconium diboride, rectangular preforms 1 and 2 are formed by compression, respectively, in a metal mold at a pressure of 150 MPa, for example, 5 mm and 5 mm thick.

Then, an intermediate layer powder mixture is prepared from zirconia and zirconium diboride powders by calculating their volume fractions in the powder mixture according to formula (1) based on their KTP. We obtain their volume fractions in the powder mixture, respectively, 61% and 39%.

Next, the thickness of the intermediate layer is calculated by the formula (2) based on the values of the thicknesses of the preforms 1 and 2, KTR of zirconium diboride equal to 6.5 × 10 ^-6 K ^-1 and zirconia, ΔT = 1400 ° C - set by the hot pressing mode of the material. We get the estimated thickness of the intermediate layer, equal to 0.11 mm.

The obtained blanks of zirconium dioxide and zirconium diboride are stacked on top of each other in a graphite mold and an intermediate layer of a powder mixture of calculated thickness is placed between them, then hot pressing is carried out at a temperature of 1400 ° C and a pressure of 20 MPa for 30 minutes in a protective nitrogen atmosphere.

Example 3

From the prepared powders of zirconium diboride and zirconium carbide, rectangular preforms 1 and 2 are formed by compression, respectively, in a metal mold at a pressure of 100 MPa, for example, 10 mm and 5 mm thick.

Then, an intermediate layer powder mixture is prepared from zirconium diboride and zirconium carbide powders by calculating their volume fractions in the powder mixture according to formula (1) based on their KTP. We obtain their volume fractions in the powder mixture, respectively, 48% and 52%.

Next, the thickness of the intermediate layer is calculated by the formula (2) based on the values of the thicknesses of the workpieces 1 and 2, KTR of zirconium diboride and zirconium carbide, ΔT = 1700 ° C - set by the mode of hot pressing of the material. We get the estimated thickness of the intermediate layer, equal to 0.17 mm

The obtained blanks of zirconium diboride and zirconium carbide are stacked on top of each other in a graphite mold and an intermediate layer of a powder mixture of calculated thickness is placed between them, then hot pressing is carried out at a temperature of 1700 ° C and a pressure of 10 MPa for 20 minutes in a protective nitrogen atmosphere.

Example 4

From the prepared powders of zirconium dioxide, zirconium diboride and zirconium carbide, rectangular blanks 1, 2 and 3 are formed by compression in a metal mold, respectively, at a pressure of 200 MPa with a thickness of, for example, 10 mm, 5 mm and 10 mm.

Then, powder mixtures of intermediate layers are prepared from zirconia, zirconium diboride and zirconium carbide powders by calculating their volume fractions in the powder mixture according to the formula (1) based on their KTP. We obtain volume fractions in the powder mixture for the first intermediate layer of zirconium dioxide, zirconium diboride, respectively 61% and 39%; for the second intermediate layer of zirconium diboride and zirconium carbide, respectively 48% and 52%.

Next, the thickness of the first intermediate layer is calculated by the formula (2) based on the values of the thicknesses of the workpieces 1 and 2, KTR of zirconium dioxide, zirconium diboride, ΔT = 1600 ° C - set by the mode of hot pressing of the material. We get the estimated thickness of the first intermediate layer, equal to 0.21 mm.

Next, the thickness of the second intermediate layer is calculated by the formula (2) based on the values of the thicknesses of the workpieces 2 and 3, KTR of zirconium diboride and zirconium carbide, ΔT = 1600 ° C - set by the mode of hot pressing of the material. We get the estimated thickness of the second intermediate layer, equal to 0.16 mm

The obtained preforms of zirconium dioxide, zirconium diboride and zirconium carbide are placed on top of each other in a graphite mold and intermediate layers of a powder mixture of calculated thickness are placed between them, then hot pressing is carried out at a temperature of 1700 ° C and a pressure of 20 MPa for 25 minutes in a protective medium nitrogen.

As a result, the heat-shielding laminated composite material of the Zr _m (OBC) _n system obtained by the proposed method does not have delamination cracks formed upon cooling during its preparation.

Also, the obtained heat-shielding laminated composite material of the Zr _m (OBC) _{n system} has high mechanical properties:

- transverse bending strength at room temperature more than 500 MPa, at 1300 ° C not less than 300 MPa;

- hardness HV 10 GPa.

Claims (4)

1. A method of obtaining a heat-protective laminated composite material of the Zr _m (OBC) _{n system} , comprising preparing powders of at least two selected compounds of the specified system, forming blanks from them and layer-by-layer stacking of blanks in a graphite mold, hot pressing, characterized in that during layer-by-layer laying between these blanks, an intermediate layer of a powder mixture of selected compounds of the specified system is placed, the volume fractions of which in the mixture are determined from the formula:

where:
α ₁ , α ₂ - CTE of the selected compounds,
V ₁ , V ₂ - volume fraction of selected compounds in the mixture,
while the thickness of the intermediate layer is calculated by the formula:

where:
ΔH is the thickness of the intermediate layer,
α ₁ , α ₂ - CTE of the selected compounds,
h ₁ , h ₂ - the thickness of the workpieces,
ΔT is the temperature difference specified by the hot pressing mode of the material. 2. The method according to p. 1, characterized in that the powders of the selected compounds are prepared by processing in a ball mill in gasoline for 80-100 hours, then the dried powders are wiped through a sieve. 3. The method according to p. 1, characterized in that the preform is formed by pressing in a mold at a pressure of 100-200 MPa. 4. The method according to p. 1, characterized in that the hot pressing is carried out at a temperature of 1400-1700 ° C, a pressure of 10-20 MPa for 20-30 minutes in a nitrogen environment.