CN110436951A

CN110436951A - A kind of low cost C/C-SiC-BN composite friction material and preparation method thereof

Info

Publication number: CN110436951A
Application number: CN201910798413.1A
Authority: CN
Inventors: 肖鹏; 李杨; 牛孜博
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2019-08-27
Filing date: 2019-08-27
Publication date: 2019-11-12

Abstract

The present invention relates to nearly full densification C/C-BN-SiC composite friction materials of a kind of low cost and preparation method thereof, it is technically characterized in that and low-density short fiber reinforced C/C-BN green body is obtained using temperature and pressure method, and combine high-temperature heat treatment and the nearly full densification C/C-BN-SiC composite friction material of melting siliconising method (LSI) preparation low cost.The technique uses staple fiber press-molding preform, h-BN matrix is introduced by directly adding h-BN powder, LSI method introduces SiC matrix and realizes nearly Quan Zhimi, relative to using other carbon fiber precast bodies and density method (CVI method and PIP method), the simple process, equipment requirement is low, and the period is short, reduces production cost to the full extent.

Description

A kind of low cost C/C-SiC-BN composite friction material and preparation method thereof

Technical field

The present invention relates to nearly full densification C/C-BN-SiC composite friction materials of a kind of low cost and preparation method thereof, and technology is special Sign is: obtaining low-density short fiber reinforced C/C-BN green body using temperature and pressure method, and combines high-temperature heat treatment and melting siliconising method (LSI) the nearly full densification C/C-BN-SiC composite friction material of preparation low cost.

Background technique

C/C-SiC composite material overcomes the brittleness feature of single silicon carbide ceramics, and it is tough can to obtain higher fracture Property, higher intensity, and more excellent thermal shock resistance；Oxidation resistance is substantially better than C/C composite material simultaneously, is a kind of 1650 DEG C of the environment temperature new type high temperature structure and function materials used are able to satisfy, but antioxidant effect under low temperature in C/C-SiC It is poor, and when with metal material antithesis, metal brake adjustment debit is hurt larger, these limit C/C-SiC friction material wider Engineer application in general field.The addition of hexagonal boron nitride can improve low temperature antioxidant effect in carbon pottery, and as lubricant component Reduce the damage to mating plate.

H-BN under 1450 DEG C, normal pressure argon atmosphere to contact angle θ=117 ± 3 ° of silicon liquid, it is nonwetting to silicon liquid, hinder Silicon liquid sprawling in hole, the carbon and Si on surface layer, which sufficiently react, generates fine and close SiC hard shell, hinders the further infiltration of silicon liquid Enter, so that siliconising process terminates ahead of time.The present invention is by high-temperature heat treatment and adjustment siliconizing treatment processes in 1680 DEG C of -1800 DEG C of completions Siliconising process effectively improves porous C/C-BN siliconising effect, can prepare nearly full densification C/C-BN-SiC.

Chinese patent literature CN106478125A (application number CN201610858805.9) discloses a kind of B₄C is modified C/C- The preparation method of SiC brake material, with B₄C is that self-healing constituent element protects carbon fiber and carbon base body, can significantly improve material Inoxidizability, but the technique introduces B by vacuum pressure impregnating method₄C matrix will lead to B4C and be unevenly distributed in green body, surface For B₄The enrichment region of C, and internal is B₄C meager set area influences the stability of the friction and wear behavior of material, and B₄C particle is friction Constituent element exacerbates the abrasion of mating plate, lacks lubricant component to adjust frictional behaviour.

Chinese patent literature CN102746015A (201210248104.5) provides a kind of reaction-sintered carbon/carbon-to-carbon Silicon-boron nitride composite friction material and preparation method thereof, one silicon carbide borazon composite friction material of reaction-sintered carbon/carbon Coefficient of friction is high, wear rate is low, and preparation process is simple, production cost is low, with short production cycle.But it is generated after technique carbonization Larger porosity, and SiC is generated by reaction-sintered in situ, it cannot achieve full densification, influence the mechanical property of friction material, rub Wipe polishing machine and antioxygenic property.

Summary of the invention

In view of the deficiencies of the prior art, the present invention provides C/C-BN-SiC is compound rubs for a kind of low cost preparation nearly full densification The process of material is wiped, simple process, equipment requirement is low, and the period is short, reduces production cost to the full extent；

H-BN and SiC, which intercouples to act on as anti-oxidant constituent element, can get more preferably antioxidant effect, and SiC matrix is Hard phase, h-BN matrix play the role of self-lubricating, can improve the friction and abrasion of composite material by adjusting matrix component Energy；

For in technique and technological difficulties: h-BN hinder silicon liquid permeate green body, the present invention by high-temperature heat treatment, quickly 1680 DEG C of -1800 DEG C of completion siliconising processes of siliconising temperature are warming up to, porous C/C-BN siliconising effect is effectively improved, can prepare Nearly full densification C/C-BN-SiC.

A kind of preparation method of the nearly full densification C/C-BN-SiC composite friction material of low cost of the present invention, including following steps It is rapid:

Step 1:

By volume, with take 30-35% carbon fiber, 0%-15% graphite powder, 10%-25%h-BN powder, 35-45% heat Curable type phenol-formaldehyde resin powder；By with the raw material compression moulding after mixing taken, C/C-BN biscuit is obtained；

Step 2:

It is gradually warming up to 850-1000 DEG C in high temperature furnace, so that resin in green body is slowly decomposed carbonization, then in nitrogen gas 2000 DEG C -2300 DEG C are warming up in atmosphere, heat preservation obtains C/C-BN porous body；

Step 3:

It weighs theoretical be placed in graphite crucible with 1.5-2.5 times of silicon amount of silicon powder to pave, C/C-BN porous body is tiled In on silicon powder and gently pressing, it is subsequently placed in vacuum high temperature furnace and carries out the nearly full densification C/C-BN-SiC compound friction of melting siliconising preparation Material after in-furnace temperature is more than 1300 DEG C, is warming up to during melting siliconising with the heating rate of at least 15 DEG C/min 1680 DEG C -1800 DEG C, and in 1680 DEG C of -1800 DEG C of heat preservations, obtain nearly full densification C/C-BN-SiC composite friction material.

Preferably, the preparation side of the nearly full densification C/C-BN-SiC composite friction material of a kind of low cost of the present invention Method, in step 1, carbon fiber by a kind of short carbon fiber and two class short carbon fibers by volume, a kind of short carbon fiber: the short carbon of two classes Fiber=3-5:1 composition；The length of one kind short carbon fiber is 5-7 millimeters, and the length of two class short carbon fibers is 10-14 milli Rice.It is realized by the cooperation of appropriate a kind of short carbon fiber and the long short carbon fiber of a kind of short carbon fiber to friction material in the present invention Coupling enhancing.

Preferably, the preparation side of the nearly full densification C/C-BN-SiC composite friction material of a kind of low cost of the present invention Method, in step 1, h-BN is in powdered, and its partial size is less than or equal to 25 microns.In the present invention, h-BN as lubricant component and Oxygen additive is hindered to use.

Preferably, the preparation side of the nearly full densification C/C-BN-SiC composite friction material of a kind of low cost of the present invention Method, in step 1, by volume, with taking 30-35% carbon fiber, 5%-15% graphite powder, 10%-25%h-BN powder, 35- 45% thermoset phenolic resin powder.

Preferably, the preparation side of the nearly full densification C/C-BN-SiC composite friction material of a kind of low cost of the present invention Method in step 1, will be packed into mold after mixing with the raw material taken；The pressure for first applying 3-10MPa, is then lifted out pressure To 20-30MPa and it is warming up to 120-160 DEG C B rank phenolic resin is adequately softened without significant under a certain pressure Crosslinking curing, keep the temperature 20-50min, flow resin viscosity, wetting fibre, hole reduce, be warming up under state of pressure keeping 170-190 DEG C, resin is heated to occur part crosslinking curing, the bubble discharge that heat preservation 20-40min generates solidification process, hole Gap healing, full densification.It is gradually then warming up to 230-320 DEG C, heat-insulation pressure keeping 1-2h in mold, so that phenolic resin is abundant Solidification.

Preferably, the preparation side of the nearly full densification C/C-BN-SiC composite friction material of a kind of low cost of the present invention Method in step 2, is warming up to 2000 DEG C -2300 DEG C in nitrogen atmosphere, keeps the temperature 2-3h, obtain the process of C/C-BN porous body In, furnace pressure 1-1.1atm.

Preferably, the preparation side of the nearly full densification C/C-BN-SiC composite friction material of a kind of low cost of the present invention Method in step 3, weighs theoretical be placed in graphite crucible with the silicon powder of silicon amount 1.5-2.5 and paves, C/C-BN porous body is put down It is laid on silicon powder and gently presses, be subsequently placed in vacuum high temperature furnace, be first warming up to 1200-1300 DEG C of heat preservation 20-40min equilibrium temperature , then it is rapidly heated with the speed of 20-50 DEG C/min to 1680 DEG C, whole process vacuumizes later, it is gradually warmed up to 1800 DEG C, 1800 DEG C of heat preservation 50-70min；Finally close vacuum pump, applying argon gas to normal pressure, sample furnace cooling.It is theoretical in the present invention to use Silicon amount refers to: needing the SiC generated during can calculating melting siliconising by the difference of porous body density before expected density and siliconising Content, so calculate Si reacted with C in theoretical silicon amount.

Preferably, the preparation side of the nearly full densification C/C-BN-SiC composite friction material of a kind of low cost of the present invention Method, the porosity of products obtained therefrom is less than 6%.

A kind of preparation method of the nearly full densification C/C-BN-SiC composite friction material of low cost of the present invention, products obtained therefrom In, the volumn concentration of BN is more than or equal to 10%.This is far beyond the content of h-BN in existing product.The present invention is logical Cooperation and control Step 2: three are crossed, to realize that the significantly addition of h-BN provides necessary condition, and obtains good production Object.

C/C-BN-SiC composite friction material coefficient of friction prepared by the present invention is relative to traditional C/C-SiC compound friction material Material, coefficient of friction is relatively low, and braking process is more steady, and smaller with revolving speed (braking condition) amplitude of variation, average friction Coefficient is between 0.5-0.6, and at pressure 0.6MPa, revolving speed 6000r/min (20m/s) friction condition, quality wear rate is 4.3mg/ times, far below the quality wear rate (13.33mg/ times) of C/C-SiC composite material.

The utility model has the advantages that

The present invention relates to a kind of processes of the nearly full densification C/C-BN-SiC composite friction material of low cost preparation.The work Skill uses staple fiber press-molding preform, introduces h-BN matrix by directly adding h-BN powder, LSI method introducing SiC matrix is simultaneously real Now nearly Quan Zhimi, relative to other carbon fiber precast bodies and thickening technology (CVI method and PIP method) are used, simple process, equipment is wanted Ask low, the period is short, reduces production cost to the full extent.

H-BN and SiC is resistance oxygen additive, and oxidation process can form the lesser mobile phase (B of viscosity₂O₃And SiO₂), The active site of carbon constituent element is covered, filling pore micro-crack hinders oxygen diffusion.And the coupling of the two can obtain more preferably Antioxidant effect.On the one hand because of B₂O₃(> 1000 DEG C) volatility is stronger under high temperature, so h-BN is suitble at 1000 DEG C or less Its antioxidant effect is played, because SiC (< 1000 DEG C) oxidation rate under middle low temperature is low and oxidation product SiO₂Lack flowing Property, so SiC can just give full play to its antioxidant effect at 1000 DEG C or more.Another aspect SiO₂With B₂O₃Produce solid solution Reduce B₂O₃Volatility, improve SiO₂Mobility promotes the oxidation of SiC.Since SiC is hard phase, to the damage of mating plate compared with Greatly, suitable h-BN and graphite are all that lubricant component has self-lubricating property, but h-BN matrix and silicon liquid are not only nonwetting but also not Reaction, it is ensured that there are enough lubrications mutually to exist after after melting siliconising.So the preparation process can be by adjusting h-BN With the ratio of SiC, improve the friction and wear behavior of composite material.The present invention is also added h-BN for large scale and provides necessity simultaneously Condition.

H-BN is nonwetting to silicon liquid, hinders silicon liquid sprawling in hole, it is fine and close that the carbon and Si on surface layer sufficiently react generation SiC hard shell, hinder the further infiltration of silicon liquid so that siliconising process ahead of time terminate.The present invention by high-temperature heat treatment, by It is rapidly heated below silicon fusing point to 1680 DEG C of -1800 DEG C of completion siliconising processes, effectively improves porous C/C-BN siliconising effect, Nearly full densification C/C-BN-SiC can be prepared.

Detailed description of the invention

Fig. 1 is the process flow chart that low cost prepares C/C-BN-SiC friction material；

Fig. 2 is C10-1 products C/C-BN-SiC brake material microstructure in the embodiment of the present invention；

Fig. 3 is braking curve figure of constant (0.6Mpa) C0 (unmodified) the carbon pottery of pressure under different braking speed；

Fig. 4 is braking curve figure of constant (0.6Mpa) C10 (modification) the carbon pottery of pressure under different braking speed.

Process flow of the invention as can be seen from Figure 1.

As can be seen from Figure 2: carbon fiber is distributed in C/C substructure unit, and resin carbon interface cohesion, to make big Part carbon fiber corrodes from silicon liquid, forms a large amount of micro-cracks after being carbonized and being heat-treated, between h-BN and resin carbon, is The infiltration of silicon liquid provides channel.Silicon liquid in siliconising process pore network is rapid along the micro-crack between resin carbon and h-BN It sprawls, and is reacted with resin carbon and generate SiC frame, staggered h-BN is distributed among SiC frame.As shown, Si liquid is exactly Matrix, since h-BN is not also reacted with silicon liquid several wettings, staggered h-BN are infiltrated along micro-crack between h-BN and resin carbon Piece hinders the flowing of silicon liquid, extends the path of silicon liquid flowing, protects C/C substructure unit from silicon to a certain extent Corrosion.

As can be seen from Figure 3: unmodified carbon pottery (C/C-SiC) increases with speed, and hind wing phenomenon is more obvious, high frequency Vibration aggravation, braking curve is more and more unstable, and when revolving speed reaches 6000r/min, in the braking later period, coefficient of friction is acutely trembled It is dynamic, along with the sound of hard hit, this is because speed is lower in the braking later period, when hard phase instant contact outstanding Between extend, being embedded between hard phase relatively deep leads to mutual clamping stagnation.

As can be seen from Figure 4: making pottery relative to unmodified carbon, h-BN carbon modified pottery (C10) coefficient of friction is lower but rubs Process is more steady, and brake noise is smaller, and when revolving speed reaches 6000r/min, it is violent braking later period coefficient of friction do not occur The phenomenon that shake, this is since C10 test ring rubbing surface hard phase is relatively fewer, and h-BN is applied to surface in friction process Play the role of lubrication, avoids the mutual clamping stagnation of hard phase.

Specific embodiment

Step 1: molding green body mixing: using 12mm and 6mm carbon fiber as reinforcement (volume ratio 4:1), pass through length fibre Dimension coupling enhancing, is 25 μm of h-BN below as lubricant component using the graphite of 1000 mesh and average particle size, is 56%B with carbon yield The phenolic resin of rank heat curing type is the presoma of adhesive and matrix carbon, and ingredient is as shown in the table, and powder raw material leads to after weighing It crosses three-dimensional material mixer to mix well, then short carbon fiber and mixed powder is stirred evenly in high-speed mixer.

Table 1. is molded green body component list

Cold pressing: solid-state mixture uniformly being filled into 150mm × 200mm mold, on a hydraulic press cold moudling, is suppressed Pressure is 5MPa.

Hot pressing: adherence pressure to 25MPa is warming up to 150 DEG C in the state that pressure is 25MPa and makes B rank phenolic resin Adequately softening is without significant crosslinking curing under a certain pressure, a hot pressing after keeping the temperature a period of time, keeps resin viscous Property flowing, wetting fibre, hole reduces, and 180 DEG C is warming up under state of pressure keeping, resin is heated to occur part crosslinking curing, heat preservation Secondary hot pressing is to predetermined thickness after 30min, so that the bubble discharge that solidification process generates, hole healing, full densification

Solidification: 280 DEG C are gradually warming up to, heat-insulation pressure keeping 2h in mold, so that phenolic resin sufficiently solidifies

Step 2: preparation porous C/C-BN green body

Carbonization: under micro-positive pressure (1.03atm), inert gas shielding, 900 DEG C of carbonizations are gradually warming up to, preparation low-density is more Hole C/C-BN green body

2. carbonization technique parameter list of table

Graphitization: under the protection of micro-positive pressure nitrogen atmosphere, C/C-BN porous body carries out 2000-2300 DEG C in high temperature furnace High-temperature heat treatment, to improve the percent opening and degree of graphitization of C/C-BN porous material.Since h-BN is in 1450 DEG C, normal pressure argon gas It is nonwetting to silicon liquid to contact angle θ=117 ± 3 ° of silicon liquid under atmosphere, hinder silicon liquid sprawling in hole, the carbon on surface layer and Si, which sufficiently reacts, generates fine and close SiC hard shell, hinders the further infiltration of silicon liquid, so that siliconising process terminates ahead of time.Graphite Change processing can be solved the problems, such as effectively due to adding h-BN to cause silicon liquid that can not penetrate into green body.

Step 3: reaction infiltration method prepares C/C-BN-SiC green body

Melting siliconising: theoretical be placed in graphite crucible with 2 times of silicon amount of silicon powder is taken to pave, by porous C/C-BN composite material Green body is laid on silicon powder and gently presses.1300 DEG C of heat preservation 30min steady temperature fields are warming up to, from 1300 DEG C of speed with 20 DEG C/min Degree is rapidly heated to 1680 DEG C, and whole process vacuumizes later, is gradually warmed up to 1800 DEG C, 1800 DEG C of heat preservation 60min.It finally closes true Sky pump, applying argon gas to normal pressure, sample furnace cooling.Reaction infiltration process is completed in 1680 DEG C to 1800 DEG C temperature sections, because 1650 DEG C or so, non-wetted-wetting transformation (θ=90 °) occurs for h-BN and silicon liquid.Contact angle is 90 ± 5 °, at 1650 DEG C or more Green body can be improved to the wetability of silicon liquid in siliconising, improves siliconising effect.By the difference of porous body density before expected density and siliconising Can calculate melting siliconising during need generate SiC content, and then calculate Si reacted with C in theory silicon amount.

5. siliconizing treatment processes parameter list of table

It is graphitized the influence to siliconising effect:

Increase through Overheating Treatment green body percent opening, siliconising effect is preferable, and remaining porosity is less after siliconising, so at heat Reason is conducive to silicon liquid infiltration green body, can effectively solve the problems, such as due to adding h-BN to cause silicon liquid that can not penetrate into green body.

Influence of the siliconizing treatment processes to siliconising effect

Traditional siliconizing treatment processes parameter:

Green body after graphitization heat treatment is by the green body parameter before and after traditional siliconizing treatment processes:

The siliconising effect of traditional siliconizing treatment processes is relatively poor, and residual percent opening is higher, mainly since h-BN powder is to silicon The nonwetting property of liquid causes, and the technique after optimizing can realize nearly Quan Zhimi.

Antioxidant effect detection

It makes pottery C0 (C/C-SiC) relative to unmodified carbon, carbon modified makes pottery (C/C-BN-SiC) C10 and C20 oxidation rate whole A temperature section (600-1300 DEG C) averagely reduces 28.54% and 53.22%, after h-BN has replaced carbon-based formulations, significantly improves The antioxidant effect of carbon pottery.

Frictional behaviour detection

Fig. 3: braking curve of constant (0.6Mpa) C0 (unmodified) the carbon pottery of pressure under different braking speed

(a) v=5m/s (b) v=10m/s (c) v=15m/s (d) v=20m/s

As speed increases, hind wing phenomenon is more obvious, high-frequency vibration aggravation, braking curve is more and more unstable, when turn When speed reaches 6000r/min, the later period is being braked, what coefficient of friction was acutely shaken, along with the sound of hard hit, this is because In the braking later period, speed is lower, and the hard phase instant contact time outstanding extends, and relatively depth is embedded between hard phase to be caused mutually to block It is stagnant.

Fig. 4: braking curve of constant (0.6Mpa) C10 (modification) the carbon pottery of pressure under different braking speed

(a) v=5m/s (b) v=10m/s (c) v=15m/s (d) v=20m/s

It makes pottery relative to unmodified carbon, h-BN carbon modified is made pottery, and (C10) coefficient of friction is lower but friction process is more steady, braking Noise is smaller, when revolving speed reaches 6000r/min, does not occur braking the phenomenon that later period coefficient of friction is acutely shaken, this is to be Since C10 test ring rubbing surface hard phase is relatively fewer, and h-BN is applied to surface in friction process and plays the role of lubrication, keeps away The mutual clamping stagnation of hard phase is exempted from.

The average friction coefficient of the said goods C10 of the present invention is between 0.5-0.6, and friction curve is more steady, in pressure 0.6MPa, revolving speed 6000r/min (20m/s), under friction condition, quality wear rate is 4.3mg/ time, and it is compound to be far below C/C-SiC The quality wear rate (13.33mg/ times) of material.

Claims

1. a kind of preparation method of the nearly densification C/C-BN-SiC composite friction material entirely of low cost, it is characterised in that: including following Step:

Step 1:

By volume, with taking 30-35% carbon fiber, 0%-15% graphite powder, 10%-25%h-BN powder, 35-45% heat curing type Phenol-formaldehyde resin powder；By with the raw material compression moulding after mixing taken, C/C-BN biscuit is obtained；

Step 2:

It is gradually warming up to 850-1000 DEG C in high temperature furnace, so that resin in green body is slowly decomposed carbonization, then in nitrogen atmosphere 2000 DEG C -2300 DEG C are warming up to, heat preservation obtains C/C-BN porous body；

Step 3:

It weighs theoretical be placed in graphite crucible with 1.5-2.5 times of silicon amount of silicon powder to pave, C/C-BN porous body is laid in silicon It on powder and gently presses, is subsequently placed in vacuum high temperature furnace and carries out the nearly full densification C/C-BN-SiC compound friction material of melting siliconising preparation Material after in-furnace temperature is more than 1300 DEG C, is warming up to 1680 during melting siliconising with the heating rate of at least 15 DEG C/min DEG C -1800 DEG C, and in 1680 DEG C of -1800 DEG C of heat preservations, obtain nearly full densification C/C-BN-SiC composite friction material.

2. a kind of preparation method of the closely full densification C/C-BN-SiC composite friction material of low cost according to claim 1, It is characterized by: in step 1, carbon fiber by a kind of short carbon fiber and two class short carbon fibers by volume, a kind of short carbon fiber: Two class short carbon fibers=3-5:1 composition；The length of one kind short carbon fiber is 5-7 millimeters, and the length of two class short carbon fibers is 10-14 millimeters.

3. a kind of preparation method of the closely full densification C/C-BN-SiC composite friction material of low cost according to claim 1, It is characterized by: h-BN is in powdered, and its partial size is less than or equal to 25 microns in step 1.

4. a kind of preparation method of the closely full densification C/C-BN-SiC composite friction material of low cost according to claim 1, It is characterized by: in step 1, by volume, with taking 30-35% carbon fiber, 5%-15% graphite powder, 10%-25%h-BN powder End, 35-45% thermoset phenolic resin powder.

5. a kind of preparation method of the closely full densification C/C-BN-SiC composite friction material of low cost according to claim 1, It is characterized by: will be packed into mold after mixing with the raw material taken in step 1；First apply the pressure of 3-10MPa, then Adherence pressure to 20-30MPa and be warming up to 120-160 DEG C make B rank phenolic resin adequately soften under a certain pressure without Significant crosslinking curing occurs, keeps the temperature 20-50min, flows resin viscosity, wetting fibre, hole is reduced, under state of pressure keeping It is warming up to 170-190 DEG C, resin is heated to occur part crosslinking curing, the bubble row that heat preservation 20-40min generates solidification process Out, hole heals, full densification.It is gradually then warming up to 230-320 DEG C, heat-insulation pressure keeping 1-2h in mold, so that phenolic aldehyde tree Rouge sufficiently solidifies.

6. a kind of preparation method of the closely full densification C/C-BN-SiC composite friction material of low cost according to claim 1, It is characterized by: being warming up to 2000 DEG C -2300 DEG C in nitrogen atmosphere in step 2,2-3h is kept the temperature, the porous base of C/C-BN is obtained During body, furnace pressure 1-1.1atm.

7. a kind of preparation method of the closely full densification C/C-BN-SiC composite friction material of low cost according to claim 1, It is characterized by: weigh theoretical be placed in graphite crucible with the silicon powder of silicon amount 1.5-2.5 in step 3 and pave, C/C-BN is more Hole green body is laid on silicon powder and gently presses, and is subsequently placed in vacuum high temperature furnace, is first warming up to 1200-1300 DEG C of heat preservation 20-40min Then steady temperature field is rapidly heated with the speed of 20-50 DEG C/min to 1680 DEG C, whole process vacuumizes later, is gradually warmed up 1800 DEG C, 1800 DEG C of heat preservation 50-70min；Finally close vacuum pump, applying argon gas to normal pressure, sample furnace cooling.

8. a kind of low cost described in -7 any one nearly full densification C/C-BN-SiC composite friction material according to claim 1 Preparation method, it is characterised in that: in products obtained therefrom, the volumn concentration of h-BN is more than or equal to 10%.

9. a kind of low cost described in -7 any one nearly full densification C/C-BN-SiC composite friction material according to claim 1 Preparation method, it is characterised in that: the porosity of products obtained therefrom is less than 6%.

10. the nearly densification C/C-BN-SiC composite friction material entirely of a kind of low cost described in -7 any one according to claim 1 Preparation method, it is characterised in that:

The coefficient of friction of products obtained therefrom is between 0.5-0.6, at pressure 0.6MPa, the friction condition of revolving speed 6000r/min, quality Wear rate is less than or equal to 4.3mg/ times.