阅读说明：本技术 一种高强高韧耐超高温金属陶瓷的制备方法 (Preparation method of high-strength high-toughness ultrahigh-temperature-resistant metal ceramic ) 是由 余艺平 肖鹏 王松 于 2021-01-12 设计创作，主要内容包括：本发明公开一种高强高韧耐超高温金属陶瓷的制备方法,该制备方法包括设计层状结构、按设计的层状结构铺填陶瓷粉体和难熔金属、生坯压制和高温烧结等步骤。本发明提供的制备方法选择难熔金属作为层状增韧相,可以减弱层状金属陶瓷烧结过程中的应力集中,充分发挥难熔金属自身和层状结构的增韧效果,在增韧相体积分数很低的情况下也可获得较好的韧性；此外,该制备方法工艺简单、周期短、环境友好,且可针对不同的应用需求,通过调整两相的排布得到不同性能的制品,工业化生产前景广阔。(The invention discloses a preparation method of high-strength high-toughness ultrahigh temperature-resistant metal ceramic. The preparation method provided by the invention selects the refractory metal as the layered toughening phase, can weaken the stress concentration in the sintering process of the layered cermet, fully exert the toughening effect of the refractory metal and the layered structure, and can obtain better toughness under the condition of very low volume fraction of the toughening phase; in addition, the preparation method is simple in process, short in period and environment-friendly, products with different properties can be obtained by adjusting the arrangement of two phases according to different application requirements, and the industrial production prospect is wide.)

1. A preparation method of high-strength high-toughness ultrahigh temperature resistant cermet is characterized by comprising the following steps:

s1: designing a layered structure of the ultrahigh temperature resistant metal ceramic, wherein the layered structure comprises ceramic layers and refractory metal layers which are alternately arranged in a laminated manner, the upper surface and the lower surface of the ultrahigh temperature resistant metal ceramic are both ceramic layers, and the layer number and the layer thickness ratio of the ceramic layers and the refractory metal layers are respectively the same;

s2: according to the designed layered structure, a layer of ceramic powder is paved in the die, and after the ceramic powder is pressed to be compact, a layer of continuous refractory metal is paved;

s3: according to the designed layered structure, repeating the paving and filling process of the ceramic powder and the refractory metal until the designed layered structure is met;

s4: moving the die into sintering equipment, vacuumizing, loading pressure and sintering;

s5: and (4) after the die is cooled to room temperature along with the furnace, opening the furnace and demoulding to obtain the high-strength high-toughness ultrahigh-temperature-resistant metal ceramic.

2. The method according to claim 1, wherein in step S1, the number of layers of the refractory metal layer is equal to or greater than 1, and the ratio of the thicknesses of the refractory metal layer and the ceramic layer is 0.1-1.

3. The method according to claim 1, wherein in step S2, the ceramic powder is at least one of boride, carbide and nitride of zirconium;

or the ceramic powder is at least one of boride, carbide and nitride of tantalum;

or the ceramic powder is at least one of boride, carbide and nitride of hafnium.

4. The method of claim 1, wherein in step S2, the refractory metal is at least one of tungsten, tantalum, and niobium.

5. The method of any of claims 1 to 4, wherein the refractory metal layer and the ceramic layer have a coefficient of thermal expansion difference of < 15%.

6. The method of claim 1, wherein the refractory metal in a continuous form is at least one of a continuous fiber, a mesh, a ribbon, and a foil.

7. The method of claim 6, wherein the refractory metal continuous fibers have a diameter of 0.3 to 0.8 mm;

the refractory metal net is formed by weaving continuous fibers with the diameter of 0.3-0.8 mm, and the mesh pores of the refractory metal net are 0.5-2 mm;

the thickness of the refractory metal wire band and the refractory metal foil is 0.2-0.8 mm.

8. The method according to claim 1, wherein in step S4, the vacuum environment after evacuation is 10Pa or less.

9. The method according to claim 1, wherein the pressure is 20 to 70MPa in step S4.

10. The method according to claim 1, wherein the sintering temperature is 2000 to 2200 ℃ in step S4.

Technical Field

The invention relates to the technical field of composite material preparation, in particular to a preparation method of high-strength high-toughness ultrahigh temperature resistant metal ceramic.

Background

Currently, hypersonic aircrafts have become the technological high point of competitive preemption of military countries in the world. Because the flying speed is very fast, when the hypersonic aerocraft reenters in the atmosphere and cruises in the atmosphere, the sharp parts such as the nose cone, the wing leading edge and the like need to bear the strict thermal oxygen coupling condition examination, and the hypersonic aerocraft provides extremely high requirements for the mechanical property, the high-temperature oxidation resistance and the ablation resistance of the thermostructural material of the aerocraft. The traditional C/C composite material has low density and excellent high-temperature strength, but has poor oxidation resistance, and can be oxidized at 400 ℃ in an aerobic environment. The refractory metal is simple in processing and forming, excellent in thermal shock resistance, large in density and rapidly reduced in strength at high temperature. Both of the above materials cannot completely match the requirements of the future aircraft with higher flying speed on the thermal structural material with light weight, high strength and high temperature oxidation resistance. Therefore, the development of new high-strength, high-toughness, ultra-high temperature resistant materials is urgently needed.

The superhigh-temperature resistant ceramic is refractory boride, carbide and nitride of some transition metals, mainly including ZrB₂，HfB₂TaC, HfC, ZrC, HfN, etc. Because the melting point is over 3000 ℃ generally, the strength and the modulus are high, the thermal conductivity, the thermal expansion coefficient and the oxidation ablation resistance are moderate, the ultrahigh temperature resistant ceramic has the potential of realizing long-time non-ablation in an oxidation environment of over 2000 ℃, and is an excellent candidate material for a key hot end component of a nose cone, a front edge and an engine combustion chamber of an aircraft and a hypersonic aircraft in the atmosphere. However, the short plate with the largest performance of the ultra-high temperature resistant ceramic has low toughness and is easy to crack under the impact of high heat flux density, so that catastrophic damage is caused, and the application of the short plate as a high-temperature structural material is also greatly limited.

The existing ultrahigh temperature resistant ceramic toughening method is complex in preparation process, and the prepared product cannot give consideration to both high toughness and high specific strength, so that the toughened ultrahigh temperature resistant ceramic falls into a bottleneck.

Disclosure of Invention

The invention provides a preparation method of high-strength high-toughness ultrahigh temperature resistant metal ceramic, which is used for overcoming the defects that the preparation process of a toughening method in the prior art is complex, and the prepared product cannot give consideration to both high toughness and high specific strength.

In order to realize the purpose, the invention provides a preparation method of high-strength high-toughness ultrahigh temperature resistant cermet, which comprises the following steps:

s1: designing a layered structure of the ultrahigh temperature resistant metal ceramic, wherein the layered structure comprises ceramic layers and refractory metal layers which are alternately arranged in a laminated manner, the upper surface and the lower surface of the ultrahigh temperature resistant metal ceramic are both ceramic layers, and the layer number and the layer thickness ratio of the ceramic layers and the refractory metal layers are respectively the same;

s2: according to the designed layered structure, a layer of ceramic powder is paved in the die, and after the ceramic powder is pressed to be compact, a layer of continuous refractory metal is paved;

s3: according to the designed layered structure, repeating the paving and filling process of the ceramic powder and the refractory metal until the designed layered structure is met;

s4: moving the die into sintering equipment, vacuumizing, loading pressure and sintering;

s5: and (4) after the die is cooled to room temperature along with the furnace, opening the furnace and demoulding to obtain the high-strength high-toughness ultrahigh-temperature-resistant metal ceramic.

Compared with the prior art, the invention has the beneficial effects that:

1. the preparation method of the high-strength high-toughness ultrahigh temperature-resistant metal ceramic provided by the invention selects refractory metal with good physical and chemical compatibility with the ceramic matrix as the layered toughening phase, can weaken stress concentration in the sintering process of the layered metal ceramic, fully exerts the toughening effect of the refractory metal and a layered structure, and can obtain better toughness under the condition of very low volume fraction of the toughening phase.

2. The preparation method of the high-strength high-toughness ultrahigh temperature resistant cermet provided by the invention comprises two steps of green pressing and high-temperature sintering. On one hand, the inside of the high-temperature resistant ceramic powder and the gaps between the high-temperature resistant ceramic powder and the refractory metal are enabled to be as small as possible by pressurizing at room temperature, so that the diffusion path of the ceramic in the sintering process is reduced, and the rapid sintering is realized; on the other hand, through high-temperature sintering, the refractory metal and the ceramic react to form interface combination with moderate strength on the premise of ensuring the densification of the product, so that the load is effectively transferred, high strength is obtained while high toughness is obtained, and the oxidation of the refractory metal or the ceramic to generate an impurity phase can be avoided by controlling the sintering vacuum degree, so that the sintering densification and the mechanical property improvement of the product are hindered.

3. Compared with the existing layered cermet preparation process, the preparation method of the high-strength high-toughness ultrahigh temperature-resistant cermet provided by the invention has the advantages of simple process, short period and environmental friendliness, can obtain products with different properties by adjusting the arrangement of two phases according to different application requirements, and has wide industrial production prospect.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

FIG. 1 is a load-displacement curve of three-point bending test of high-strength, high-toughness and ultrahigh-temperature-resistant cermet in examples 1-5.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of those skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination of technical solutions should not be considered to exist, and is not within the protection scope of the present invention.

The drugs/reagents used are all commercially available without specific mention.

The invention provides a preparation method of high-strength high-toughness ultrahigh temperature resistant cermet, which comprises the following steps:

s1: designing a layered structure of the ultrahigh temperature resistant metal ceramic, wherein the layered structure comprises ceramic layers and refractory metal layers which are alternately arranged in a laminated manner, the upper surface and the lower surface of the ultrahigh temperature resistant metal ceramic are both ceramic layers, and the layer number and the layer thickness ratio of the ceramic layers and the refractory metal layers are respectively the same;

s2: according to the designed layered structure, a layer of ceramic powder is paved in the die, and after the ceramic powder is pressed to be compact, a layer of continuous refractory metal is paved;

s3: according to the designed layered structure, repeating the paving and filling process of the ceramic powder and the refractory metal until the designed layered structure is met;

s4: moving the die into sintering equipment, vacuumizing, loading pressure and sintering;

s5: and (4) after the die is cooled to room temperature along with the furnace, opening the furnace and demoulding to obtain the high-strength high-toughness ultrahigh-temperature-resistant metal ceramic.

Preferably, in step S1, the number of layers of the refractory metal layer is equal to or greater than 1, and the layer thickness ratio between the refractory metal layer and the ceramic layer is 0.1-1. For the material with the layered structure, when other factors are unchanged, the larger the layer number is, the higher the toughness of the material is, and the lower the strength is; when the total thickness and the number of layers are fixed, the thickness ratio of the layers is too large, which is not favorable for the toughness of the laminated ceramic, and the thickness ratio of the layers is too small, which is not favorable for the strength of the laminated ceramic. The number of the refractory metal layers is designed to be more than or equal to 1, the layer thickness ratio of the refractory metal layers to the ceramic layers is designed to be 0.1-1, the expansion path of cracks in the material is prolonged as far as possible on the premise that the product has moderate strength, and the toughness of the material is improved.

Preferably, in step S2, the ceramic powder is at least one of boride, carbide and nitride of zirconium;

or the ceramic powder is at least one of boride, carbide and nitride of tantalum;

or the ceramic powder is at least one of boride, carbide and nitride of hafnium.

Preferably, in step S2, the refractory metal is at least one of tungsten, tantalum, and niobium.

Preferably, the refractory metal layer and the ceramic layer have a coefficient of thermal expansion difference of < 15%.

The refractory metal with better physical and chemical compatibility with the ceramic matrix is selected as the layered toughening phase, so that the stress concentration in the sintering process of the layered cermet can be weakened, the toughening effect of the refractory metal and the layered structure can be fully exerted, and better toughness can be obtained under the condition of low volume fraction of the toughening phase.

Preferably, the refractory metal in continuous form is at least one of a continuous fiber, a mesh, a ribbon, a foil. A large number of researches show that under the condition of a certain volume fraction of the toughening phase, the improvement range of the toughness of the composite material has a close relation with the appearance of the toughening phase. Generally, the toughening phase with large length-diameter ratio has better toughening effect than the granular toughening phase, and the flaky toughening phase has better toughening effect than the fibrous toughening phase. After the continuous fibers are woven to form the two-dimensional fabric, the two-dimensional fabric is reinforced due to axial and radial constraint, so that the stress dissipation is facilitated, and the toughening effect is greatly improved.

Preferably, the diameter of the refractory metal continuous fiber is 0.3-0.8 mm;

the refractory metal net is formed by weaving continuous fibers with the diameter of 0.3-0.8 mm, and the mesh pores of the refractory metal net are 0.5-2 mm;

the thickness of the refractory metal wire band and the refractory metal foil is 0.2-0.8 mm.

The diameter of the refractory metal continuous fibers, the thickness of the refractory metal ribbon and the refractory metal foil directly determine the thickness of the refractory metal layer in the article. For the layered structure material, the thickness of the hard layer (ceramic layer) and the soft layer (refractory metal layer) influences the failure mode of the product, and the thinner soft layer can be bent more greatly to divide the crack into more sections along the thickness direction, thereby improving the fracture toughness of the product. However, the thickness of the refractory metal layer is not smaller, and the thickness is preferably smaller, because of the limitation of the process conditions, the thickness reduction can cause local deformation of the refractory metal layer in the sintering process, the thickness uniformity is reduced, and the probability of defect introduction at the interface is increased.

The mesh porosity of the refractory metal mesh has a large impact on the performance of the article: the grid pores are too large, two layers of ceramic powder can be in full contact, sintering densification at high temperature is facilitated, but the defects are that the thickness of a ceramic layer in an obtained product can deviate from that of a ceramic layer designed in advance, the capability of the refractory metal net for resisting deformation in the axial direction is weakened, and the toughening effect can be reduced; the mesh pores are too small, the refractory metal mesh has better overall mechanical property and prominent toughening effect, but the difficulty of weaving processing is increased, and the two layers of ceramic powder are not fully contacted and are difficult to sinter and densify.

Preferably, in step S4, the post-vacuum environment is 10Pa or less. At high temperatures of approximately 2000 ℃, metals and ceramics have very high reactivity, in particular with respect to O atoms. When the vacuum in the furnace is higher than 10Pa, the metal and the ceramic are easily oxidized to generate oxide impurities which are distributed at the crystal boundary, thereby not only hindering the sintering densification of the product, but also damaging the mechanical property and the high temperature resistance of the product.

Preferably, in the step S4, the pressure is 20-70 MPa. Sintering densification is a prerequisite to impart macroscopic properties to ceramics. The ceramic powder has high melting point, strong chemical bond bonding among atoms and low self-diffusion coefficient, and is very difficult to densify by high-temperature sintering. And the pressure is loaded during sintering, so that the ceramic particles in the green body can be more tightly stacked, the contact area is increased, the surface tension offset by closed pores in the green body can be compensated, and the sintering densification of the product is accelerated. For a ceramic material, when the loading pressure is lower than 20MPa, the pressure has no obvious effect on promoting sintering densification of the material, but when the loading pressure is higher than 70MPa, the pressure not only provides a strict test for the bearing capacity of a mould, but also easily causes cracks to grow in the material.

Preferably, in step S4, the sintering temperature is 2000-2200 ℃. Sintering temperature is an important factor affecting sintering. Along with the rise of the temperature, the vapor pressure of the material is increased, the diffusion coefficient is increased, the viscosity is reduced, so that the processes of evaporation-condensation, ion and vacancy diffusion, particle rearrangement, viscous plastic flow and the like are accelerated, and the sintering densification of the ceramic is facilitated. For high-strength high-toughness ultrahigh-temperature-resistant metal ceramics, a sample with high density is difficult to obtain by sintering at the temperature of below 2000 ℃, but the reaction degree of a refractory metal phase and a ceramic phase is aggravated by increasing the sintering temperature, so that the thickness of an interface layer is increased, and the thickness of the metal phase is reduced. Comprehensively considering, the high-strength high-toughness ultrahigh temperature resistant metal ceramic which is relatively compact and has moderate interface layer thickness can be obtained by taking 2000-2200 ℃ as sintering temperature.

Example 1

The embodiment provides a preparation method of a high-strength high-toughness ultrahigh temperature resistant cermet, which comprises the following steps:

(1) weighing 24g (the thickness is about 1.4mm after densification) of TaC and HfC mixed powder, putting the powder into a circular graphite die (d is 40mm), and scraping the powder by a scraper;

(2) compacting the powder by using an upper die, and putting the powder into a pre-cut Ta foil (the thickness is 0.2 mm);

(3) 24g of TaC and HfC mixed powder (the thickness is about 1.4mm after being compacted) is paved on the Ta foil, and the Ta foil is scraped by a scraping blade and compacted by an upper die;

(4) after die assembly, compacting the green body powder by a hydraulic press at the pressure of 2MPa, putting the green body powder into a discharge plasma sintering furnace, and vacuumizing until the air pressure in the furnace is lower than 10 Pa;

(5) heating from room temperature to 1500 ℃ at the speed of 100 ℃/min, and loading pressure from 0 to 40 MPa; heating from 1500 deg.C to 2000 deg.C at a rate of 50 deg.C/min, holding for 10min, and cooling to obtain Ta with metal phase volume fraction of 7.14%_Foila/TaC/HfC cermet.

The bending strength is 436.5MPa by adopting a three-point bending method according to GB/T6569-2006; the fracture toughness K is measured by adopting a single-edge prefabricated corrugated beam (SEPB) method according to GB/T23806-_ICIs 7.76MPa · m^1/2(ii) a By correlation of the integrated area of the load-displacement curve (as shown in FIG. 1) from a three-point bendThe work of rupture is 1204J/m by calculation of formula²。

Example 2

This example is different from example 1 in that the sintering temperature in step (5) is 2100 ℃.

The bending strength is 558.9MPa by adopting a three-point bending method according to GB/T6569-2006; the fracture toughness K is measured by adopting a single-edge prefabricated corrugated beam (SEPB) method according to GB/T23806-_ICIs 8.48 MPa.m^1/2(ii) a The fracture work is 1520J/m according to the integral area of the load-displacement curve (shown in figure 1) of three-point bending and calculated by a correlation formula²。

Example 3

This example differs from example 1 in that the sintering temperature in step (5) is 2200 ℃.

The bending strength is 282.7MPa by adopting a three-point bending method according to GB/T6569-2006; the fracture toughness K is measured by adopting a single-edge prefabricated corrugated beam (SEPB) method according to GB/T23806-_ICIs 9.17 MPa.m^1/2(ii) a The breaking work is 509J/m calculated by a correlation formula according to the integral area of a load-displacement curve (shown in figure 1) of three-point bending²。

Example 4

This example is different from example 2 in that the loading pressure in step (5) is from 0 to 20 MPa.

The bending strength is 742.9MPa by adopting a three-point bending method according to GB/T6569-2006; the fracture toughness K is measured by adopting a single-edge prefabricated corrugated beam (SEPB) method according to GB/T23806-_ICIs 8.42 MPa.m^1/2(ii) a The breaking work is 2868J/m calculated by a correlation formula according to the integral area of a load-displacement curve (shown in figure 1) of three-point bending²。

Example 5

This example is different from example 2 in that the loading pressure in step (5) is from 0 to 50 MPa.

The bending strength is 578.8MPa by adopting a three-point bending method according to GB/T6569-2006; the fracture toughness K is measured by adopting a single-edge prefabricated corrugated beam (SEPB) method according to GB/T23806-_ICIs 7.45 MPa.m^1/2(ii) a Load-displacement curve according to three-point bendingThe integrated area (shown in FIG. 1) is calculated by the correlation formula to obtain the work-to-break of 1547J/m²。

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.