OXIDATION-INDUCED SHAPE MEMORY FIBER AND PREPARATION METHOD AND APPLICATION THEREOF

Abstract

The present disclosure relates to an oxidation-induced shape memory fiber comprising a tension-bearing core material and/or a tension-bearing core material coated with an antioxidative coating, and an oxidizable pressure-bearing coating. The oxidizable pressure-bearing coating is coated outside the tension-bearing core material and/or the tension-bearing core material coated with an antioxidative coating; the oxidizable pressure-bearing coating is in compressive stress state and/or the tension-bearing core material coated with an antioxidative coating and the oxidizable pressure-bearing coating are in tension-compression balance state. The disclosure also relates to preparation and application thereof, the preparation is: reserving anchoring end, exerting tension force on tension-bearing core material and/or tension-bearing core material coated with an antioxidative coating, followed by coating oxidizable pressure-bearing coating thereon. The oxidation-induced shape memory fiber is applicable to high temperature oxidation environment.

Claims

1. An oxidation-induced shape memory fiber, characterized in that the oxidation-induced shape memory fiber comprises a tension-bearing core material and an oxidizable pressure-bearing coating, the oxidizable pressure-bearing coating is coated outside of the tension-bearing core material and the end of the tension-bearing core material is not coated with the oxidizable pressure-bearing coating; the end of the tension-bearing core material which is not coated with the oxidizable pressure-bearing coating is defined as an anchoring end; under the equivalent oxidation conditions and experimental situations, the oxidation speed of the oxidizable pressure-bearing coating is bigger than the oxidation speed of the tension-bearing core material; the oxidizable pressure-bearing coating is in a compressive stress state along the length direction of the tension-bearing core material; and the tension-bearing core material and the oxidizable pressure-bearing coating are in a tension-compression balance state along the length direction of the tension-bearing core material.

2. The oxidation-induced shape memory fiber according to claim 1, characterized in that the tension-bearing core material is composed of an antioxidative material or a non-antioxidative material coated with an antioxidative material coating.

3. The oxidation-induced shape memory fiber according to claim 1, characterized in that an extremely oxidizable coating is arranged between the tension-bearing core material and the oxidizable pressure-bearing coating; the cross-section of the oxidation-induced shape memory fiber is the tension-bearing core material, the extremely oxidizable coating and the oxidizable pressure-bearing coating from inside to the outside in succession, under the equivalent oxidation conditions and experimental situations, the antioxidative ability of the three materials, namely tension-bearing core material, the oxidizable pressure-bearing coating and the extremely oxidizable coating, decreases successively while the cross-section oxidation loss rate increases successively; the oxidizable pressure-bearing coating is in a compressive stress state along the length direction of the tension-bearing core material; and the tension-bearing core material and the oxidizable pressure-bearing coating are in a tension-compression balance state along the length direction of the tension-bearing core material.

4. The oxidation-induced shape memory fiber according to claim 1, characterized in that the outer surface of the end or other positions of the memory fiber is coated with a second antioxidative coating; the sections where the surface of the end or other positions of the memory fiber is coated with the second antioxidative coating are defined as reinforced anchoring ends.

5. The oxidation-induced shape memory fiber according to claim 1, characterized in that the oxidation environment includes at least one of gas oxidation and liquid oxidation; the core material is chosen from at least one of C, SiC, B.sub.4C and metal fiber; the antioxidative coating is chosen from at least one of SiC, B.sub.4C, ZrC, TiC, HfC, TaC, NbC, Si.sub.3N.sub.4, BN, AN, TaN, CrSi.sub.2, MoSi.sub.2, TaSi.sub.2, WSi.sub.2, HfSi.sub.2, Nb.sub.5Si.sub.3, V.sub.5Si.sub.3, CrB.sub.2, TiB.sub.2, ZrB.sub.2 or the multiphase composite coating Hf—Ta—C and Hf—Si—C or is multilayer coated; the oxidizable pressure-bearing coating is chosen from a C coating and a carbon-rich coating.

6. The oxidation-induced shape memory fiber according to claim 1, characterized in that the anchoring end plays a role of anchoring within a matrix; the anchor type of the anchoring end is chosen from the anchoring type with an exposed end; the exposed length of the anchoring type with an exposed end is l′; the l′ meets the formula: $l^{'} \geq \frac{d σ_{f 1}}{4 \bar{τ}} .$

7. A preparation method for the oxidation-induced shape memory fiber according to claim 1, characterized in that reserving an anchoring end, exerting tension force on the core material or the core material with an antioxidative coating; then preparing a layer of oxidizable pressure-bearing coating on the surface thereof; removing the tension force to obtain a sample; or reserving an anchoring end, exerting tension force on the core material or the core material with an antioxidative coating; then preparing a layer of oxidizable pressure-bearing coating on the surface thereof; removing the tension force, followed by coating a second antioxidative layer on a preset part of the oxidizable pressure-bearing coating; or reserving an anchoring end, exerting tension force on the core material or the core material with an antioxidative coating; then preparing a layer of extremely oxidizable coating on the surface thereof, followed by coating an oxidizable pressure-bearing coating outside thereof; removing the tension force to obtain a sample; the exerted tension force is 30% to 90% of the bearing force for the tension-bearing fiber or the tension-bearing fiber with the antioxidative coating.

8. The preparation method for the oxidation-induced shape memory fiber according to claim 7, characterized in that in the whole oxidation-induced shape memory fiber, in order to allow the prestressing force exerted on the outside by the memory fiber to reach the maximum, the optimal acquisition method is: under the condition that the cross-sectional area of the oxidation-induced shape memory fiber is constant, the magnitude of the prestressing force storage for the memory fiber is closely related to the volume fraction V.sub.f of the tension-bearing fiber and the axial force F of the tension-bearing fiber is $\begin{matrix} F = σ_{f}^{p} A_{f} = \frac{E_{c} V_{c} σ_{o} A_{f}}{E_{c} V_{c} + E_{f} V_{f}} = \frac{E_{c} V_{c} σ_{o} V_{f} A}{E_{c} V_{c} + E_{f} V_{f}} = \frac{(1 - V_{f}) V_{f}}{E_{c} (1 - V_{f}) + E_{f} V_{f}} E_{c} σ_{o} A & (14) \end{matrix}$ when F reaches the maximum, prestressing force to the outside from memory fiber will reach the maximum; to calculate the extremum of the axial force for the tension-bearing fiber, firstly differentiating F: $\begin{matrix} F^{'} = \frac{(1 - 2 V_{f}) [E_{c} (1 - V_{f}) + E_{f} V_{f}] - (V_{f} - V_{f}^{2}) (E_{f} - E_{c})}{{[E_{c} (1 - V_{f}) + E_{f} V_{f}]}^{2}} E_{c} σ_{o} A & (15) \end{matrix}$ that is $\begin{matrix} F^{'} = \frac{(E_{c} - E_{f}) V_{f}^{2} - 2 E_{c} V_{f} + E_{c}}{{[E_{c} (1 - V_{f}) + E_{f} V_{f}]}^{2}} E_{c} σ_{o} A & (16) \end{matrix}$ taking F′=0:
(E.sub.c−E.sub.f)V.sub.f.sup.2−2E.sub.cV.sub.f+E.sub.c=0 (17) when E.sub.c=E.sub.f, then V.sub.f=½, at this time F can take extremum, namely the Fmax; $V_{f}^{2} - \frac{2 E_{c}}{E_{c} - E_{f}} V_{f} + \frac{E_{c}}{E_{c} - E_{f}} = 0,$ when E.sub.c≠E.sub.f, specific to the equation taking $a = \frac{E_{c}}{E_{c} - E_{f}},$ since E.sub.c>0, E.sub.f>0 then a<0 or a>1, so Δ=4a.sup.2−4a>0, the original equations have two different real roots: $\begin{matrix} V_{f} = a \pm \sqrt{a^{2} - a} = \frac{E_{c} \pm \sqrt{E_{c} E_{f}}}{E_{c} - E_{f}} = \frac{1 \pm \sqrt{E_{f} / E_{c}}}{1 - E_{f} / E_{c}} & (18) \end{matrix}$ further since 0<V.sub.f<1, when E.sub.c<E.sub.f, then $V_{f} = \frac{1 + \sqrt{E_{f} / E_{c}}}{1 - E_{f} / E_{c}} < 0;$ when E.sub.c>E.sub.f, then $V_{f} = \frac{1 + \sqrt{E_{f} / E_{c}}}{1 - E_{f} / E_{c}} > 1,$ and then the real root $V_{f} = \frac{1 + \sqrt{E_{f} / E_{c}}}{1 - E_{f} / E_{c}}$ does not meet the condition of 0<V.sub.f<1 and should be abandoned; and when $\begin{matrix} V_{f} = a - \sqrt{a^{2} - a} = \frac{E_{c} - \sqrt{E_{c} E_{f}}}{E_{c} - E_{f}} & (19) \end{matrix}$ V.sub.f meets the condition of formula 19 and can allow F to take the maximum value, namely Fmax.

9. An application of the oxidation-induced shape memory fiber according to claim 1, characterized in that the oxidation-induced shape memory fiber is applied to reinforce the matrix; the matrix includes at least one of a ceramic matrix, a metal matrix and a concrete matrix and when the oxidation-induced shape memory fiber is applied in the ceramic matrix or the metal matrix, its volume consumption is 20-80 v %.

10. The application of the oxidation-induced shape memory fiber according to claim 9, characterized in that when the material of the matrix is SiC and the core material of the oxidation-induced shape memory fiber is SiC fiber, the oxidizable pressure-bearing coating is C coating; when the material of the matrix is SiC and the core material of the oxidation-induced shape memory fiber is C fiber with SiC coating, the oxidizable pressure-bearing coating is C coating; when the oxidation-induced shape memory fiber is applied in the ultra-high temperature ceramic phase of Zr—Ti—C—B quaternary boron carbide and the core material of the oxidation-induced shape memory fiber is C fiber with SiC coating, the oxidizable pressure-bearing coating is a C coating or carbon-rich B.sub.x—C or carbon-rich Si.sub.y—C, wherein x≤2, y≤0.5.

11. The application of the oxidation-induced shape memory fiber according to claim 9, characterized in that the oxidation-induced shape memory fiber is applied in the reinforced matrix to obtain a composite material with self-healing function; in addition to configuring the memory fiber in the self-healing composite material, it further needs to anchor the memory fiber in the matrix and the antioxidantive ability of the matrix is higher than that of pressure-bearing coating of the memory fiber; the pressure-bearing coating comprises a carbon-rich pressure-bearing coating.

12. The application of the oxidation-induced shape memory fiber according to claim 9, characterized in that the antioxidantive ability of each constitute of the self-healing composite material reinforced by the oxidation-induced shape memory fiber meet the following conditions: the tension-bearing core material and the matrix>the oxidizable pressure-bearing coating>the extremely oxidizable coating.

13. The application of the oxidation-induced shape memory fiber according to claim 11, characterized in that the atomic ratio of C element in the carbon-rich pressure-bearing coating is bigger than the elemental stoichiometric ratio of the normal compounds and the stoichiometric ratio of M, K and C elements in carbon-rich M.sub.x-K.sub.yC pressure-bearing coating meets x+y custom-character 2, wherein M represents at least one of IVA group metal elements or absence thereof, K represents at least one elements of B, Si, N or absence thereof.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0145] FIG. 1 is the preparation principle of the shape memory fiber;

[0146] FIG. 2 is the shape restoration mechanism of the oxidation-induced shape memory fiber;

[0147] FIG. 3 is the self-healing principle map for the oxidation driven memory fiber;

[0148] FIG. 4 is the self-healing principle map for the memory fiber with an eternal anchoring end;

[0149] FIG. 5 is the self-healing principle map of the tension-bearing fiber coated with the antioxidative protection coating;

[0150] FIG. 6 is the self-healing principle map of the tension-bearing fiber coated with the extremely oxidizable coating;

[0151] FIG. 7 is the schematic map for the type of the memory fiber;

[0152] FIG. 8 is the stereo schematic map of the anchoring end;

[0153] FIG. 9 is the mechanic model of the memory fiber;

[0154] FIG. 10 shows that changes to the dosage and the initial tensile stress of the memory fiber influence the prestressing force of the matrix;

[0155] FIG. 11 is the schematic map of the simple device for the continual preparation memory fiber;

[0156] FIG. 12 is the schematic map of the finite element model;

[0157] FIG. 13 is the schematic map of the unit grid division;

[0158] FIG. 14 is the schematic map of comparison result for the simulated oxidation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0159] Sample Calculation for the Memory Fiber Reinforced Composite Material

[0160] Basic Parameters of the Material

[0161] The pressure-bearing coating of the memory fiber adopts C coating, the tension-bearing fiber adopts SiC fiber and the preparation method for the pressure-bearing coating adopts CVD method. When the volume fraction (v %) of the tension-bearing fiber is 14.2 v %, the volume fraction of the pressure-bearing coating is 85.8 v % and the prestressing force stored in the tension-bearing fiber reaches the maximum. The dosage of the memory fiber in the composite material is 50 v %, basic parameters of the pressure-bearing coating, the tension-bearing fiber and the matrix are shown in table 1. As materials of the tension-bearing fiber and the matrix are the same and the swelling coefficients are the same, after the pressure-bearing coating is oxidized, there is no thermal stress between the tension-bearing fiber and the matrix. The anchoring manner of the memory fiber in the matrix adopts the anchoring type with an exposed end. Namely by subjecting C coating in the end of the SiC tension-bearing fiber in the memory fiber to erosion treatment or by avoiding C coating in the end of the SiC tension-bearing fiber, the SiC tension-bearing fiber with an exposed end is directly bonding and anchoring within the matrix, the length l′ of the anchoring end is ≥50d (d is the diameter of the fiber).

TABLE-US-00001 TABLE 1 basic parameters for the pressure-bearing coating, the tension-bearing fiber and the matrix material type C material SiC pressure- tension- bearing bearing SiC material parameter coating fiber matrix elasticity modulus/Gpa 11 400 400 volume fraction 85.8%*50% 14.2%*50% 50% initial tension stress σ.sub.0 — 2000 MPa —

[0162] The maximum axial stress of the matrix:

[0163] assuming that the memory fiber is monodirectionally and uniformly distributed in the matrix, the cross-section of the pressure-bearing coating is lost and the compressive stress exerted on the matrix by the retraction of the memory fiber shape restoration reaches the maximum value.

[0164] the stress stored in the tension-bearing fiber is:

[00044] $\begin{matrix} σ_{f}^{p} = \frac{1 1 \times 1 0^{3} \times 85.8 % \times 2000}{1 1 \times 1 0^{3} \times 85.8 % + 400 \times 1 0^{3} \times 14.2 %} = 2 8 5 & (MPa) \end{matrix}$

[0165] the prestressing force exerted on the matrix by the retraction of the tension-bearing fiber is:

[00045] $\begin{matrix} σ_{m}^{p} = - \frac{4 0 0 \times 1 0^{3} \times 7.1 % \times 285}{4 0 0 \times 1 0^{3} \times 7.1 % + 400 \times 1 0^{3} \times 50 %} = - 3 5.4 & (MPa) \end{matrix}$

[0166] It can be known from the above calculation results that the precompressive stress exerted on the matrix by the memory fiber reaches 35.4 MPa and if the volume fraction of the memory fiber and the initial tension force of the tension-bearing fiber continue to increase, then the compressive stress exerted on the matrix will continue to increase.

[0167] As shown in FIG. 10, when the volume fraction V.sub.s of the memory fiber and the initial tension force σ.sub.o of the tension-bearing fiber continue to increase, the precompressive stress of the matrix will continue to increase. Therefore, the size of the compressive stress can be controlled by the size and volume fraction of the initial tension stress of the memory fiber, which means the exertion of pressure press can contribute to close cracks of the matrix, decrease the stress concentration, increase the rigidity, improve the antioxidantive ability and improve the tenacity.

Embodiment 1

[0168] The tension-bearing fiber of the memory fiber in the present embodiment adopts SiC fiber, the pressure-bearing coating of the tension-bearing fiber adopts the oxidative C coating and the matrix material is SiC ceramics material. The memory fiber adopts the anchoring type with an exposed end and without the oxidative coating, namely the end exposed with the SiC tension-bearing fiber is bonding and anchoring with the SiC matrix and the length of the anchoring end is no less than 50d.

[0169] The tension-bearing fiber adopts SiC fiber with a diameter about 11 μm. The continual preparation device of deposing the oxidative coating is shown in FIG. 11, wherein the SiC fiber enters the deposition furnace from the fibril emitting reel to deposit the coating and then furl the fibril receiving reel. During the deposition process, a constant tension force is exerted by adjusting the loading pulley to allow the initial tension stress σ.sub.o of the SiC fiber to maintain 1800 MPa. The cleavage structure of the SiC core memory fiber is SiC core/C coating, namely the pyrolytic carbon pressure-bearing coating (oxidative pressure-bearing coating) is deposited on the surface of the SiC tension-bearing fiber. The method that the SiC pressure-bearing fiber deposits C coating is as follow:

[0170] The chemical vapor deposition (CVD) is adopted to deposit C coating, wherein the initial tension stress of the SiC tension-bearing fiber is 1800 MPa, the gas source adopts the mixing gas of propylene and tetrachloromethane with the respective gas flow being 500 ml/min and 400 ml/min, the deposition temperature is 1000° C., the pressure within the deposition furnace is 0.5-1.5 kPa, the fibril movement speed o the fiber in the furnace is 1 mm/min and the whole process is protected by argon. When the coating reaches the designed thickness, the deposition is finished, the tension force of the fiber is removed and the deposition furnace is cooled to room temperature, wherein the thickness of the pyrolytic carbon oxidative pressure-bearing coating is about 5 μm.

[0171] An oxidation-induced shape memory fiber with a diameter about 21 μm can be prepared by the above-mentioned method and the pressure-bearing coating of the memory fiber is the C coating with a thickness of 5 μm. The C coating with a length about 5 mm in the end of the SiC tension-bearing fiber of the memory fiber is removed by slight erosion to pre-reserve the anchoring end exposed with the SiC tension-bearing fiber, namely the end exposed with the SiC tension-bearing fiber is bonding and anchoring within the matrix. Then the oxidation-induced shape memory fiber is compiled into a prefab and the density of the prefab is 0.9 g/cm.sup.3. The chemical vapor infiltration (CVI) is adopted to prepare the memory fiber reinforced SiC ceramics matrix self-healing composite material and the preparation method is:

[0172] The prefab is put into a normal isothermal CVI deposition furnace to perform SiC deposition, wherein the deposition temperature is 1100° C., the raw gas adopts argon or nitrogen as the diluent gas with a gas flow of 900 ml/min, methyltrichlorosilane is chosen as the reaction gas and the flow of methyltrichlorosilane is 1.0 g/min, hydrogen is chosen as the vector and the flow of hydrogen is 500 ml/min, the reaction period is 200 hours, and the density of the finally prepared memory fiber reinforced SiC ceramics matrix self-healing composite material is 2.3 g/cm.sup.3.

Embodiment 2

[0173] The tension-bearing fiber of the memory fiber in the present embodiment adopts SiC fiber, the pressure-bearing coating adopts the oxidative carbon-rich B—C coating and the matrix material is SiC ceramics material. The memory fiber adopts the anchoring type with an exposed end and without the oxidative coating, namely the end exposed with the SiC tension-bearing fiber is bonding and anchoring with the SiC matrix and the length of the anchoring end is no less than 50d.

[0174] The tension-bearing fiber adopts SiC fiber with a diameter about 11 μm. The continual preparation device of deposing the oxidative coating is shown in FIG. 11, wherein the SiC fiber enters the deposition furnace from the fibril emitting reel to deposit the coating and then furl the fibril receiving reel. During the deposition process, a constant tension force is exerted by adjusting the loading pulley to allow the initial tension stress σ.sub.o of the SiC fiber to maintain 1800 MPa. The cleavage structure of the SiC core memory fiber is SiC core/pyrolytic C coating/carbon-rich B—C coating, namely the first coating of the SiC tension-bearing fiber is pyrolytic C coating (transition layer) and the second coating is the carbon-rich B—C coating (oxidative pressure-bearing coating). Each deposition step for the coating of the SiC tension-bearing fiber is as follow:

[0175] step 1: the first coating is deposited by the chemical vapor deposition (CVD), wherein a constant tension force is exerted by the loading pulley to allow the initial tension stress σ.sub.o of the SiC tension-bearing fiber to be 1800 MPa, then the coating is continually deposited on the surface of the SiC tension-bearing fiber, the gas source for deposition adopts the mixing gas of propylene and tetrachloromethane with the respective gas flow being 400 ml/min and 400 ml/min, the deposition temperature is 1000° C., the internal pressure of the deposition furnace is 0.5-1.3 kPa, the fibril movement speed of the fiber in the furnace is 200 mm/min, the whole process is protected by argon, the deposited pyrolytic C coating with the thickness of 0.1 μm is obtained and the pyrolytic C coating is firstly oxidized by the entered oxidation mediums to quicken the restoration speed of the memory fiber.

[0176] step 2: the second coating is deposited on the surface of the first coating with the same method and the tension force is the same with that in step 1, wherein the reaction gas for deposition is CH.sub.4, BCl.sub.3 and hydrogen, the diluent gas is argon, the fibril movement speed of the fiber in the furnace is 3 mm/min and the deposition temperature is 1100° C. The gas flow of CH.sub.4, BCl.sub.3 and hydrogen is respectively 500 ml/min, 400 ml/min and 1200 ml/min, the gas flow of argon is 600 ml/min, the pressure is 9-10 KPa, when the coating reaches the designed thickness, the deposition is finished, the tension force of the fiber is removed and cooled to room temperature to obtain the carbon-rich B—C ceramics coating with a thickness about 4.2 μm, wherein the stoichiometric ratio of B element and C element in the carbon-rich B—C ceramics coating is about 1.2:1.

[0177] A SiC core oxidation-induced shape memory fiber with a diameter about 19.6 μm can be prepared by the above-mentioned method and the pressure-bearing coating of the memory fiber is the second coating, i.e. the carbon-rich B—C ceramics coating with a thickness of 4.2 μm. The surface pyrolytic C coating with a length about 5 mm in the end of the SiC core and carbon-rich B—C coating are removed by slight erosion and alkali to pre-reserve the anchoring end exposed with the SiC core, namely the end exposed with the SiC tension-bearing fiber is bonding and anchoring with the SiC matrix. Then the memory fiber is compiled into a prefab and the density of the prefab is 1 g/cm.sup.3. The chemical vapor infiltration (CVI) is adopted to prepare the memory fiber reinforced SiC ceramics matrix self-healing composite material and the preparation method is:

[0178] The prefab is put into a normal isothermal CVI deposition furnace to perform SiC matrix deposition, wherein the deposition temperature is 1100° C., the raw gas adopts argon or nitrogen as the diluent gas with a gas flow of 900 ml/min, methyltrichlorosilane is chosen as the reaction gas and the flow thereof is 1.0 g/min, hydrogen is chosen as the vector and the flow of hydrogen is 500 ml/min, the reaction period is 220 hours, and the density of the finally prepared memory fiber reinforced SiC ceramics matrix self-healing composite material is 2.2 g/cm.sup.3.

Embodiment 3

[0179] The present embodiment adopts the C fiber coated with the SiC protection coating as the tension-bearing fiber and the pressure-bearing coating adopts the oxidative coating, the matrix material is SiC ceramics material. The length for the anchoring end of the memory fiber is no less than 50d and the anchoring end adopts the anchoring type with an exposed end and without the oxidative coating to ensure that the end of C core fiber coated with the SiC protection coating is bonding and anchoring with the SiC matrix.

[0180] C fiber adopts the PAN matrix T1000 carbon fiber produced by TORAY INDUSTRIES, INC. and the diameter of C fiber is about 5 μm. Before the deposition of the coating, the colloid on the surface of C fiber is removed by refluxing acetone, C fiber is immersed in the acetone solution of 70° C. in the reflux device for 48 hours to remove the colloid on the surface of C fiber, and then the carbon fiber is taken out and dried. The continual preparation device of deposing the oxidative coating is shown in FIG. 11, wherein the SiC fiber enters the deposition furnace from the fibril emitting reel to deposit the coating and then furl the fibril receiving reel. During the deposition process, a constant tension force is exerted by adjusting the loading pulley to allow the initial tension stress σ.sub.o of the SiC fiber to maintain 2000 MPa. The cleavage structure of the SiC core memory fiber is C fiber/pyrolytic C coating/SiC coating/C coating, wherein the first coating of the C fiber is composed of the pyrolytic C coating (transition layer) and the second coating is SiC coating (protection coating) and the third coating is C coating (oxidative pressure-bearing coating). Deposition steps for each coating of C fiber are as follow:

[0181] step 1: the first coating is deposited by the chemical vapor deposition (CVD), wherein the initial tension stress σ.sub.o of the SiC tension-bearing fiber to be 2000 MPa, the gas source adopts the mixing gas of propylene and tetrachloromethane with the respective gas flow being 400 ml/min and 400 ml/min, the deposition temperature is 1000° C., the internal pressure of the deposition furnace is 0.5-1.3 kPa, the fibril movement speed of the fiber in the furnace is 200 mm/min, the whole process is protected by argon, the deposited pyrolytic C coating with the thickness of 0.1 μm is obtained to improve the interface bonding of the C fiber and the SiC protection coating.

[0182] step 2: the second coating is deposited on the surface of the first coating with the CVD method and the tension force of the fiber is the same with that in step 1, wherein the reaction gas adopts methyltrichlorosilane and hydrogen is vector with a vector gas flow of 400 ml/min, the diluent gas is argon with a gas flow of 500 ml/min, the pressure is 18 KPa, the fibril movement speed of the fiber in the furnace is 120 mm/min and the deposition temperature is 1000° C. and the tension-bearing fiber is obtained by deposition, which has SiC coating with a thickness of about 0.4 nm as the protection coating of C fiber, namely it has the antioxidative protection coating with the C fiber as the core.

[0183] step 3: the third coating is continued to deposit on the surface of the second coating with the CVD method and the tension force of the fiber is the same with that in step 1. The gas source adopts the mixing gas of propylene and tetrachloromethane with the respective gas flow being 500 ml/min and 400 ml/min, the deposition temperature is 1000° C., the fibril movement speed of the fiber in the furnace is 5 mm/min, the whole process is protected by argon. When the coating reaches the designed thickness, the deposition is finished, the tension force of the fiber is removed and the deposition furnace is cooled to room temperature to obtain the pyrolytic carbon oxidative pressure-bearing coating with a thickness about 3.8 μm.

[0184] An oxidation-induced shape memory fiber with a diameter about 13.6 μm is prepared through the above-mentioned three steps and the pressure-bearing coating of the memory fiber is third coating, namely the pyrolytic carbon with the thickness of 3.8 μm. The end of C fiber coated with the SiC protection coating is subjected to slight erosion to remove C coating with a length about 5 mm on the surface of the SiC protection coating and to expose the SiC protection coating and bond and anchor within the matrix. Then the oxidation-induced shape memory fiber is compiled into a prefab and the density of the prefab is 0.4˜0.6 g/cm.sup.3, the memory fiber reinforced SiC ceramics matrix self-healing composite material is prepared by the chemical vapor infiltration (CVI) and the embedding method, steps thereof are as follow:

[0185] step 4: the pyrolytic carbon deposited on the prefab is densified with the isothermal CVI process, wherein the deposition uses the soaking vacuum induced gas phase deposition furnace, the deposition temperature is 1100° C., the precursor of the carbon source adopts the diluent gas of propylene (CH.sub.4) and hydrogen (H.sub.2) and the volume ratio of CH.sub.4 to H.sub.2 is 1:2, the deposition goes on for about 200 hours to prepare the porous memory fiber/carbon composite material with a density about 1.4 g/cm.sup.3.

[0186] step 5: the above-mentioned densified composite material is put into high temperature reaction furnace to perform the silicon permeation by melting, wherein the dosage of silicon powder used for embedding is 1.2 times of the theoretical demanding value, the purity of the silicon powder is 99% and the granularity is 0.01-0.1 mm. The reaction furnace is vacuumized to −0.1 MPa, the vacuum is kept for 30 minutes, argon is aerated to the normal pressure, the temperature in the furnace is increased to 1500° C. 1600° C. at a speed of 5° C./min and the heat is preserved for 1-2 hours, then it is cooled to room temperature at the speed of 10° C./min to obtain the memory fiber reinforced SiC ceramics matrix self-healing composite material with a density about 2.0 g/cm.sup.3.

Embodiment 4

[0187] The present embodiment adopts the C fiber coated with the SiC protection coating as the tension-bearing fiber, the pressure-bearing coating adopts the oxidative carbon-rich B—C coating and the matrix material is SiC ceramics material. The length of the anchoring end in the memory fiber is no less than 50d and the anchoring end adopts the anchoring type with an exposed end and without the oxidative coating to ensure that the end of the tension-bearing fiber bonds and anchors with the SiC matrix.

[0188] Before the deposition of the coating, the colloid on the surface of C fiber is removed by refluxing acetone, C fiber is immersed in the acetone solution of 70° C. in the reflux device for 48 hours to remove the colloid on the surface of C fiber, and then the carbon fiber is taken out and dried. The continual preparation device of deposing the oxidative coating is shown in FIG. 11, wherein the SiC fiber enters the deposition furnace from the fibril emitting reel to deposit the coating and then furl the fibril receiving reel. During the deposition process, a constant tension force is exerted by adjusting the loading pulley to allow the initial tension stress σ.sub.o of the SiC fiber to maintain 2000 MPa. The cleavage structure of the memory fiber is C fiber/pyrolytic C coating/SiC coating/carbon-rich B—C coating, namely the first coating of the C fiber is composed of the pyrolytic C coating (transition layer) and the second coating is SiC coating (protection coating) and the third coating is carbon-rich B—C coating (oxidative pressure-bearing coating). Deposition steps of each coating of C fiber are as follow:

[0189] step1: the first coating is deposited by the chemical vapor deposition (CVD), wherein the initial tension stress σ.sub.o of the C fiber is 2000 MPa, the gas source adopts the mixing gas of propylene and tetrachloromethane with the respective gas flow being 400 ml/min and 400 ml/min, the deposition temperature is 1000° C., the internal pressure of the deposition furnace is 0.5-1.3 kPa, the fibril movement speed of the fiber in the furnace is 200 mm/min, the whole process is protected by argon and a pyrolytic C coating with the thickness of 0.1 μm is obtained to improve the interface bonding of the C fiber and the SiC protection coating.

[0190] step 2: the second coating is deposited on the surface of the first coating with the CVD method and the tension force of the fiber is the same with that in step 1. methyltrichlorosilane is chosen as the reaction gas, hydrogen as the vector with the vector gas flow of 400 ml/min, argon as the diluent gas with the gas flow of 500 ml/min, the pressure is 18 KPa, the fibril movement speed of the fiber in the furnace is 120 mm/min, the deposition temperature is 1000° C. and the tension-bearing fiber is obtained by deposition, which has SiC coating with a thickness of about 0.4 μm as the protection coating of C fiber, namely it has the antioxidative protection coating with the C fiber as the core.

[0191] step 3: the third coating is continued to deposit on the surface of the second coating with the CVD method and the tension force of the fiber is the same with that in step 1. The gas source for deposition adopts CH.sub.4, BCl.sub.3 and hydrogen, the fibril movement speed of the fiber in the furnace is 4 mm/min, the deposition temperature is 1100° C. The gas flow of CH.sub.4, BCl.sub.3 and hydrogen is respectively 500 ml/min, 500 ml/min and 1000 ml/min, the gas flow of argon is 600 ml/min, the pressure is 9-10 KPa, when the coating reaches the designed thickness, the deposition is finished, the tension force of the fiber is removed and cooled to room temperature to obtain the carbon-rich B—C ceramics coating with a thickness about 3.3 μm, wherein the stoichiometric ratio of B element and C element in the carbon-rich B—C ceramics coating is about 1.6:1.

[0192] An oxidation-induced shape memory fiber with a diameter about 12.6 μm can be prepared by the above-mentioned three steps and the pressure-bearing coating of the memory fiber is the third coating, i.e. the carbon-rich B—C ceramics coating with a thickness of 3.3 μm. The end of C fiber coated with the SiC protection coating is washed with slight erosion and strong alkali to remove carbon-rich B—C coating with a length about 5 mm on the surface of the SiC protection coating to expose SiC protection coating and bond and anchor within the matrix. Then the oxidation-induced shape memory fiber is compiled into a prefab and the density of the prefab is 1.3 g/cm.sup.3. The chemical vapor infiltration (CVI) is adopted to prepare the memory fiber reinforced SiC ceramics matrix self-healing composite material and the preparation method is:

[0193] The prefab is put into a normal isothermal CVI deposition furnace to perform SiC deposition, wherein the deposition temperature is 1100° C., the raw gas adopts argon as the diluent gas with a gas flow of 900 ml/min, methyltrichlorosilane is chosen as the reaction gas and the flow thereof is 1.0 g/min, hydrogen is chosen as the vector and the flow of hydrogen is 500 ml/min, the reaction period is 200 hours, and the density of the finally prepared memory fiber reinforced SiC ceramics matrix self-healing composite material is 2.15 g/cm.sup.3.

Simulation Verification for Values of Closing the Crack:

[0194] 1, A finite element model is built with parameters in embodiment 1, and the finite element model is shown in FIG. 12, wherein the memory fiber enforce SiC ceramics matrix self-healing composite material is composed of A member, B member and the memory fiber, the overall size of the model is 60.1 mm×12 mm×4 mm (length×width×thickness) and the memory fiber is arranged and distributed along the length direction of the model. There is a perforative crack with a width of 0.1 mm preserved between A member (30 mm×12 mm×4 mm) and B member (30 mm×12 mm×4 mm) of the model and the SiC matrix, which acts as the channel of the oxidation mediums. Both the two A and B members of the model are connected with 12 member fibers whose length is 58.9 mm and diameter is 1 mm and the tension-bearing fiber of each fiber adopts the SiC fiber whose diameter is 0.6 mm and the strength is 3000 MPa, wherein the anchoring ends exposed on both ends all have the length of 1.2 mm. The initial tension stress of the SiC tension-bearing fiber by pre-exerting stress is 2000 MPa, the pressure-bearing coating is C coating and the thickness is 0.2 mm. The model grind division is shown in FIG. 13, the size of grids in the matrix is 0.2 mm and the pressure-bearing coating, the tension-bearing fiber and the matrix units are treated with conode. All unit nodes on the end face of A member in the model are restrained in the x axis direction, wherein the node in the lower right corner of outside end face is restrained in yz plane, other nodes in the outside end face are free on the yz plane and the entire B member is free. The environment temperature is set as 800° C., the air pressure is 1 barometric pressure and it is a pure oxygen environment. The oxidation speed of the SiC material is set as 0.01 mm/min and the oxidation speed of the C coating material is set as 5 mm/min. The hardware used in the present simulation is a computer; the Hypermesh software is used to build the model and the ANSYS finite element analysis software is used to perform equivalent simulation analysis; of course, all software including finite element software such as ABAQUS that can realize the present simulation function can be used in the present disclosure.

[0195] The models in the control group is basically the same with the memory fiber enforce SiC ceramics matrix self-healing composite material model and the distinction lies in that there is not mechanic and interactive force between the SiC fiber in the control group and the C coating, namely after the C coating of the reinforced fiber is oxidized and corroded, retraction does not occur in the SiC core fiber.

[0196] 2, The simulation oxidation contrast phenomenon and process are shown in FIG. 14, wherein the left figure shows the memory fiber forced composite material, a cross-section loss occurs in the C coating in the crack after 10 s of oxidation, an extremely small closing occurs in the crack, the width of the crack becomes 0.06 mm after 120 s and the crack is completely closed after 240 s; the right figure shows the control group, wherein a cross-section loss occurs in the C coating in the crack and the width of the crack is observed with no changes after 10 s of oxidation, the width of the crack is still observed with no changes after 120 s and there is no changes observed in the width of the crack after 240 s.

[0197] 3, conclusions: it can be discovered from the simulation results that as self-healing function occurs in the memory fiber enforce SiC ceramics matrix self-healing composite material, during the oxidation experiment process and when the oxidation mediums enters the internal of the material to oxidize the C pressure-bearing coating to allow the memory fiber to be excited and retracted, exert pressure on the SiC matrix, close cracks, cut the oxidation channel, which can improve the antioxidantive ability of the composite material; however as the reinforced fiber in the test piece of the control group does not have memory function, after C coating simulation is oxidized and lost, the SiC fiber will not retract and exert pressure on the matrix to close the matrix, the C pressure-bearing coating will continue to be oxidized by the oxidation mediums from the outside and the fiber inside of the material will continue to be oxidized, which can result in the structural invalidation of the composite material very easily; therefore, it has obvious advantages to adopt the memory fiber in self-healing and antioxidantive ability aspect.

[0198] Of course, the above explanation is merely a preferred embodiment of the present disclosure, and the present disclosure is not limited to the above embodiment. It should be noted that all equivalent replacements made by those skilled in the art under the teaching of the present specification are within the essential scope of the present specification, and it should be protected by the present disclosure.

OXIDATION-INDUCED SHAPE MEMORY FIBER AND PREPARATION METHOD AND APPLICATION THEREOF

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