CN110304924B

CN110304924B - A kind of layered structure silicon carbide composite material and preparation method thereof

Info

Publication number: CN110304924B
Application number: CN201910524883.9A
Authority: CN
Inventors: 韩永军; 罗晓强; 曹迪; 詹云妮; 王文强; 王涛涛
Original assignee: Pingdingshan University
Current assignee: Pingdingshan University
Priority date: 2019-06-18
Filing date: 2019-06-18
Publication date: 2021-12-14
Anticipated expiration: 2039-06-18
Also published as: CN110304924A

Abstract

The invention relates to a layered structure silicon carbide composite material and a preparation method thereof. Specifically, the present invention uses two kinds of silicon carbide powders with different particle sizes, graphite, carbon black and toughening phase titanium powder as the main mixed raw materials, polyvinylpyrrolidone K90 and K30 as dispersants, polyammonium methacrylate CE- 64 is a water reducing agent. Two kinds of slurries of SiC system and SiC+Ti system are prepared respectively. After mixing uniformly, a grouting process is used to make a ceramic green body of a sandwich structure composite material of SiC/SiC+Ti/SiC system. Then the finished ceramic matrix composites were prepared by reactive sintering of embedded silicon powder, and the effect of different Ti powder contents on the properties of the composites was studied.

Description

Silicon carbide composite material with layered structure and preparation method thereof

Technical Field

The invention relates to the technical field of ceramic material preparation, in particular to a silicon carbide composite material with a laminated structure prepared by slip casting and reaction sintering processes, which can be used for aerospace, nuclear energy and the like.

Background

The SiC ceramic material is a novel material gradually developed in the 80 s of the 20 th century, and has good development and application prospects in the aspects of aerospace, military machinery, internal combustion engines, flame nozzles and the like due to light weight, high strength, large elastic modulus and high thermal conductivity. However, the poor toughness of the silicon carbide ceramic material prepared by reaction sintering causes the silicon carbide material to be difficult to process, reduces the yield of manufactured products and limits more application fields of the silicon carbide ceramic material. Compounding is an important way to improve the performance of a single ceramic. In recent years, the improvement of the strength and toughness of silicon carbide materials has become a core problem in the research of ceramic materials. At present, methods such as particle dispersion toughening, continuous fiber toughening, phase change toughening, composite toughening, nano toughening and the like are successively provided aiming at the brittleness of the SiC ceramic material, and certain effects are obtained, but all the methods have respective defects. Therefore, the method for improving the toughness of the silicon carbide ceramic is explored, and the method has very wide market space and good economic and social benefits.

Disclosure of Invention

Based on the analysis, the invention adopts a laminated structure toughening and second phase toughening composite toughening method, and prepares the laminated structure silicon carbide composite material through slip casting and reactive sintering processes. The structural toughening design mechanism is based on that external energy is consumed by the coordinated transverse shrinkage of crack passivation of lamellar structure toughening and second-phase particle toughening to further improve the toughness of the ceramic material, when the ceramic product is subjected to external load, the crack deflects or bends at the joint between the base layer and the interlayer, so that part of the stress concentration at the front end of the crack is released, the non-consumed external energy still stretches the complex-phase ceramic material, at the moment, the second-phase particles with high elastic modulus contained in the interlayer can prevent the complex-phase ceramic matrix from transversely shrinking, the external longitudinal tensile stress is increased and is coordinated with the transverse shrinkage, so more external energy is consumed, and the second phase particles are easy to disperse, the prepared composite ceramic material has good compactness, and the two are combined with each other finally, so that the toughness of the ceramic material is further enhanced. The silicon carbide composite material with better mechanical property can be more widely applied to the fields of industry, aerospace, military and the like, so that the silicon carbide composite material has wider application space.

The invention takes silicon carbide powder, graphite, carbon black and toughening phase titanium powder with two different particle sizes as main mixed raw materials, takes polyvinylpyrrolidone K90 and K30 as dispersing agents and CE-64 (ammonium polymethacrylate) as a water reducing agent to respectively prepare two kinds of slurry of a SiC system and a SiC + Ti system, and adopts a slip casting process to prepare the ceramic biscuit of the sandwich structure composite material of the SiC/SiC + Ti/SiC system after uniform mixing. Then, a ceramic matrix composite finished product is prepared by embedding silicon powder and reaction sintering, and the influence of different Ti powder contents on the performance of the composite is researched.

Specifically, the invention provides a silicon carbide composite material with a laminated structure, which comprises a sandwich structure of a SiC/SiC + Ti/SiC system.

In a preferred embodiment, the Ti occupies 0.1 to 30% by weight of the interlayer SiC + Ti.

In a preferred embodiment, the Ti occupies 15% by weight of the interlayer SiC + Ti.

The preparation method of the silicon carbide composite material with the layered structure comprises the following steps:

s1: adding a dispersing agent into distilled water, then adding a water reducing agent, a surfactant, carbon black and graphite, and stirring for a period of time; adding silicon carbide SiC, and continuously stirring for a certain time until the viscosity is maintained at 800-900 mPa.s to obtain a first slurry;

s2: dividing said first slurry into a first portion of slurry and a second portion of slurry;

s3: adding metal Ti powder into the first slurry to prepare SiC + Ti interlayer slurry;

s4: adding ethanolamine into the second part of slurry to regulate the pH value and controlling the pH value to be 8-11; then injecting the second part of slurry containing SiC and the first part of slurry containing SiC and Ti into a gypsum mould in sequence by adopting a slip casting process to form a silicon carbide-based ceramic green compact with a laminated structure of SiC/SiC + Ti/SiC, and standing for a period of time for demoulding;

s5: dehydrating, drying and degumming the green body obtained by demoulding;

s6: and sintering the ceramic biscuit after the water drainage and degumming to obtain a sintered product.

One preferred scheme is that the silicon carbide comprises powder with the grain diameter of F240 and the grain diameter of F1200, and polyvinylpyrrolidone K90 and K30 are used as dispersing agents; CE-64 is used as a water reducing agent; ethanolamine is used as a viscosity regulator; deionized water was used as the dispersion medium. The two particle size fractions F240 and F1200 particle sizes cooperate to produce a more compact effect than a single particle size.

One preferable scheme is that 2g of K90 is weighed in S1 and dispersed into 30g of distilled water, 0.2gCE-64, 0.1g of polyvinylpyrrolidone K30, 5g of carbon black and 4g of graphite are sequentially added, 35g of F1200 silicon carbide and 56g of F240 silicon carbide are added after stirring for a period of time according to the stirring condition, F1200 is not easy to disperse compared with F240 and needs to be added for a plurality of times at intervals, then mechanical stirring is carried out for 48 hours until slurry is dispersed, and the viscosity is measured at 800-900 mPa.s by a rotational viscometer at room temperature;

in S4, placing the demoulded green body into a drying oven to be dehydrated and dried at 200 ℃ until the quality of the ceramic green body is not reduced, then placing the ceramic green body dried to constant weight into a furnace body, gradually heating to 700 ℃ and preserving heat for 3 hours to carry out degumming;

in S5, embedding the ceramic biscuit after draining and degumming by using boron nitride mixed powder with the silicon content of 18%, then placing the ceramic biscuit in a vacuum hot-pressing sintering furnace to perform reaction sintering in the nitrogen atmosphere, wherein the sintering temperature is 1700 ℃, and keeping the temperature for 1h, so that silicon in the embedded powder reacts with carbon in the ceramic body to generate silicon carbide, and the silicon carbide permeates into pores of the ceramic body by capillary force to improve the compactness of the ceramic body, thereby obtaining a sintered product.

The invention has the technical advantages that: the laminated structure composite metal Ti powder silicon carbide composite material prepared by slip casting and reactive sintering processes has good inhibition and coordination effects on cracks generated under the action of external load, and can be well applied to carbon in various industrial fields by utilizing the toughness of the silicon carbide composite material. The preparation method has the advantages of simple preparation process, easy operation, capability of preparing products with complex shapes, lower reaction sintering temperature, shorter sintering time, cost reduction and convenience for batch production.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIGS. 1 and 2 XRD patterns of layered structure composite metal Ti silicon carbide composite green body and finished product of the present invention.

FIG. 3 is an SEM image of a layered structure of a green composite of silicon carbide and Ti metal in accordance with the present invention.

FIG. 4 is an SEM image of a finished laminated-structure metal Ti-clad silicon carbide composite material of the present invention.

FIG. 5 is a graph showing the bending strength of the silicon carbide composite material of the present invention in which metal Ti is laminated.

FIG. 6 is a graph showing fracture toughness of a silicon carbide composite material of a layered structure of composite metal Ti according to the present invention.

Detailed Description

The technical solution in the embodiments of the present invention is clearly and completely described below with reference to the drawings in the embodiments of the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

The preparation method of the silicon carbide composite material with a layered structure and composite metal Ti of the embodiment comprises the following steps:

silicon carbide (F240 and F1200) powder with two different particle sizes, carbon black and graphite are used as main raw materials, metal Ti powder is used as an interlayer reinforcing phase, and polyvinylpyrrolidone K90 and K30 are used as dispersing agents; CE-64 is used as a water reducing agent; ethanolamine is used as a viscosity regulator; deionized water was used as the dispersion medium.

The process of the specific embodiment is as follows:

(1) weighing 2g of K90, dispersing into 30g of distilled water, sequentially adding 0.2gCE-64 g of (ammonium polymethacrylate), 0.1g K30, 5g of carbon black and 4g of graphite, stirring for a period of time according to the stirring condition, then adding 35g of F1200 and 56g of F240, adding F1200 at intervals for several times because the F1200 is not easy to disperse compared with the F240, then mechanically stirring for 48 hours until the slurry is dispersed, and testing the viscosity at the room temperature of a rotational viscometer to be 800-900 mPa.s;

(2) adding metal Ti powder into a part of the slurry prepared in the step (1) to prepare SiC + Ti interlayer slurry;

(3) ethanolamine is added according to the viscosity of the slurry to adjust the pH value to be about 8-11. Then injecting SiC slurry and SiC + Ti slurry into a gypsum mould in sequence by adopting a slip casting process to form a SiC/SiC + Ti/SiC laminated structure silicon carbide-based ceramic green body, standing for a period of time and demoulding;

(4) placing the demoulded green body into a drying oven to be dehydrated and dried at 200 ℃ until the quality of the ceramic green body is not reduced any more, then placing the ceramic green body dried to constant weight into a furnace body, gradually heating to 700 ℃ and preserving heat for 3 hours to degum;

(5) embedding the ceramic biscuit after draining and degumming by using boron nitride mixed powder with the silicon content of 18%, then placing the ceramic biscuit in a vacuum hot-pressing sintering furnace to perform reaction sintering in the nitrogen atmosphere, wherein the sintering temperature is 1700 ℃, and preserving heat for 1h, so that silicon in the embedded powder reacts with carbon in the ceramic biscuit to generate silicon carbide, and the silicon carbide permeates into pores of the ceramic biscuit by capillary force to improve the compactness of the ceramic biscuit to obtain a sintered product;

wherein the content of the added metal Ti powder is 0-30%.

FIGS. 1 and 2 show the line diffraction patterns of a green body of a silicon carbide composite ceramic to which metal Ti powder is added in various amounts and reaction sintering at 1700 ℃, and it can be seen from FIG. 1 that the ceramic green body contains SiC as a main crystal phase, part of C, metal Ti and part of TiC, because when the ceramic green body is naturally air-dried in the air, part of carbon reacts with titanium to directly carbonize to produce titanium carbide; as can be seen from fig. 2, the amount of SiC in the main crystal phase in the sintered ceramic sample increases, while the diffraction peak of C hardly exists, and the diffraction peak of silicon occurs because the content of silicon is excessive during the sintering process, so that the pores in the silicon carbide ceramic are filled with excess silicon to form residual silicon. This shows that the silicon carbide ceramic green body is successfully sintered into a silicon carbide composite material product with good compactness through reaction sintering.

The appearance characteristics of the silicon carbide composite material green compact of the sandwich structure composite metal Ti are determined by SEM, as shown in figure 3, (a), (b) and (c) respectively show an electron microscope image of the silicon carbide composite material green compact with the metal Ti content of 8%, 15% and 30% in the sandwich SiC + Ti, the materials of the ceramic green compact are uniformly distributed from the (a), (b) and (c), and carbon black, graphite and metal Ti powder are uniformly distributed and filled in gaps of silicon carbide particles, so that air holes are fine and dispersed, the silicon carbide structure is loose at the moment, the mechanical property is small, and when the metal Ti powder content is 15% of the sandwich SiC + Ti, the whole structure of the silicon carbide ceramic green compact is uniform and compact.

FIG. 4 shows SEM images of the morphology of the finished silicon carbide composite material with sandwich structure of composite metal Ti, wherein (A), (B) and (C) respectively show the electron microscope images of the finished silicon carbide composite material with sandwich SiC + Ti with metal Ti content of 8%, 15% and 30%. As can be seen from the figure, the sample of the sintered product has good compactness, gaps in the middle of the large-particle silicon carbide raw material before reaction sintering are filled with the silicon carbide generated by the reaction, the whole structure is compact and uniform, and the structural performance is good. After reaction sintering, the pores in the silicon carbide ceramic green body are well filled with silicon carbide generated by the reaction of carbon and silicon, the addition of the metal Ti powder plays a certain role in compacting the structure of the composite material, and particularly when the metal Ti powder occupies 15% of the SiC + Ti content in the interlayer, the metal Ti powder is uniformly distributed in the silicon carbide pores, and the compactness and the mechanical property of the silicon carbide material are optimal.

As shown in fig. 5, the bending strength of the silicon carbide composite material with a laminated structure of composite metal Ti is shown, from which it is apparent that the bending strength of the composite silicon carbide ceramic material with a sandwich structure and a sandwich composite structure containing different contents of metal Ti powder are both significantly improved, from which it is seen that the bending strength of the composite material with a sandwich structure shows a tendency of increasing first and then decreasing, when the content of metal Ti in the sandwich layer is 15%, the bending strength of the composite material reaches up to 321 MPa, but when the content of metal Ti powder in the sandwich layer exceeds 15%, the bending strength of the composite material with a sandwich structure shows a sharp tendency of decreasing, which indicates that the bending strength of the silicon carbide composite material is best to make the content of metal Ti powder 15%.

As shown in FIG. 6, the fracture toughness of the silicon carbide composite material samples with different metal Ti powder contents was tested, and it can be seen from the graph that the fracture toughness of the composite silicon carbide ceramic material with the sandwich structure and the sandwich composite structure containing different metal Ti powder contents is 3.20 MPa × m^1/2The fracture toughness of the above reaction-sintered silicon carbide without adding the reinforcing phase was 3.1 MPa x m^1/2Obviously, the fracture toughness of the composite material is obviously improved, the fracture toughness of the composite material with the sandwich structure shows a trend of increasing firstly and then decreasing from the figure, and when the content of metal Ti in the sandwich layer is 15%, the fracture toughness of the composite silicon carbide ceramic with the sandwich structure reaches 6.79 MPa x m at most^1/2However, when the content of the metal Ti powder in the interlayer exceeds 15%, the fracture toughness of the sandwich interlayer composite silicon carbide ceramic shows a tendency to decrease.

The dispersing agent, the water reducing agent and the surfactant can also adopt other existing chemical reagents. The surfactant is, for example, a nonionic surfactant, and the water reducing agent is, for example, a melamine water reducing agent or a polycarboxylic acid water reducing agent.

It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all 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.

Claims

1. A method for preparing a silicon carbide composite material with a laminated structure is characterized by comprising the following steps:

s1: adding a dispersing agent into distilled water, then adding a water reducing agent, a surfactant, carbon black and graphite, and stirring for a certain time; adding silicon carbide SiC, continuously stirring for a certain time, and keeping the viscosity at 800-900 mPa.s to obtain first slurry, wherein the silicon carbide comprises powder with the particle size of F240 and powder with the particle size of F1200, and polyvinylpyrrolidone K90 and K30 are used as dispersing agents; CE-64 is used as a water reducing agent; ethanolamine is used as a viscosity regulator; deionized water is used as a dispersion medium;

s3: adding metal Ti powder into the first part of slurry to prepare SiC + Ti interlayer slurry;

s5: dehydrating, drying and degumming the green body obtained by demolding, wherein the interlayer SiC and Ti account for 0.1-30% by weight of Ti;

s6: sintering the ceramic biscuit after draining and degumming to obtain a sintered product: in the step, the ceramic biscuit after draining and degumming is embedded by boron nitride mixed powder with the silicon content of 18 percent, then the ceramic biscuit is placed in a vacuum hot-pressing sintering furnace to be sintered in a reaction mode under the nitrogen atmosphere, the sintering temperature is 1700 ℃, the temperature is kept for 1h, silicon in the embedded powder reacts with carbon in the ceramic body to generate silicon carbide, and the silicon carbide permeates into pores of the ceramic body through capillary force to improve the compactness of the ceramic body, so that a sintered product is obtained.

2. The method for producing a layered structure silicon carbide composite material according to claim 1,

weighing 2g of K90 in S1, dispersing into 30g of distilled water, sequentially adding 0.2gCE-64, 0.1g of polyvinylpyrrolidone K30, 5g of carbon black and 4g of graphite, stirring for a period of time, then adding 35g of F1200 silicon carbide and 56g of F240 silicon carbide, adding F1200 for several times at intervals, mechanically stirring for 48 hours until the slurry is dispersed, and testing the viscosity at 800-900 mPa.s by a rotational viscometer at room temperature;

and in S5, placing the demoulded green body into a drying oven to be dehydrated and dried at 200 ℃ until the quality of the ceramic green body is not reduced, then placing the ceramic green body dried to constant weight into a furnace body, gradually heating to 700 ℃, and preserving heat for 3 hours to carry out degumming.

3. The method for producing a silicon carbide composite material having a layered structure according to claim 1, wherein the interlayer SiC + Ti is occupied by Ti in a proportion of 15% by weight.