A spindle-shaped agglomerate toughened boron carbide ceramic and its preparation method

Abstract

The present invention discloses a spindle-shaped agglomerate toughened boron carbide ceramic and a preparation method thereof, belonging to the technical field of boron carbide ceramic toughening. w ‑T) introduces boron carbide (B4C) ceramics, and finally obtains spindle-shaped TiB2‑SiC agglomerates with unique structure to strengthen and toughen B4C ceramics. w and SiC w The study of thermal stability at 1600℃~1800℃ under vacuum conditions, as well as the formation mechanism, microstructure, mechanical properties and toughening mechanism of spindle-shaped TiB2‑SiC agglomerates as toughening phases and the thermal stress simulation of the system, showed that two types of spindle-shaped TiB2‑SiC agglomerates with interlocking grains were successfully synthesized inside the ceramic through the in situ reaction of B4C and Ti3SiC2 coatings.

Description

Technical Field

[0001] The invention relates to the technical field of boron carbide ceramic toughening, and in particular to a spindle-shaped agglomerate toughened boron carbide ceramic and a preparation method thereof. Background Art

[0002] Boron carbide (B4C) is a known superhard material. It has high hardness (>30GPa), low density (2.52g / cm 3 ), high melting point (>2400℃) and high neutron absorption capacity (3.47×10 -22 cm 2 ) are commonly used in industry, protective armor / coatings, and aerospace. Boron carbide composite ceramic materials are composite materials made of boron carbide as the main component and supplemented with other reinforcing materials. They have good thermal stability, acid and alkali resistance, low density, high hardness, high elastic modulus, and high thermal conductivity.

[0003] The existing toughened boron carbide composite ceramic materials include whisker toughened boron carbide composite ceramic materials, SiC coating toughened boron carbide composite ceramic materials and second phase dispersion toughened boron carbide ceramic composite materials. However, all of the above materials have the following problems: First, due to the poor thermal stability of whiskers, the performance improvement of whisker toughened boron carbide ceramics is limited and cannot achieve a better toughening effect; second, the material made of molten silicon and SiC w The SiC coating formed to protect the whiskers can improve the stability of the whiskers, but it will introduce a large amount of residual silicon into the boron carbide matrix, reducing the mechanical properties of the composite ceramic material; thirdly, boron carbide toughened by second phases such as silicon carbide particles and titanium diboride particles can achieve a certain toughening effect, but this toughening effect is only particle toughening and cannot introduce residual compressive stress for toughening, so the toughening effect is still limited. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a spindle-shaped agglomerate toughened boron carbide ceramic and a preparation method thereof, which effectively solves the following problems: First, due to the poor thermal stability of whiskers in the existing technology, the toughening effect of boron carbide ceramic materials is poor; second, the second-phase toughened ceramic material only has particle toughening and cannot introduce residual compressive stress, thereby failing to further improve the toughening effect of the composite ceramic material. At the same time, a spindle-shaped TiB2-SiC agglomerate with two interlocked grains is successfully synthesized inside the ceramic through the in-situ reaction of B4C and Ti3SiC2 coatings, and finally a spindle-shaped TiB2-SiC agglomerate-toughened B4C ceramic with a unique structure is obtained.

[0005] The first object of the present invention is to provide a spindle-shaped agglomerate toughened boron carbide ceramic, wherein the spindle-shaped agglomerates are distributed in the boron carbide ceramic as a toughening phase, the spindle-shaped agglomerates are an interlocking structure of TiB2 and SiC particles, and the aspect ratio of the spindle-shaped agglomerates is 3 to 15.

[0006] As a preferred embodiment, the spindle-shaped agglomerate toughened boron carbide ceramic has a relative density of ≥96%, a Vickers hardness of 30-35 GPa, and a fracture toughness of 4-6 MPa·m 1 / 2 .

[0007] A second object of the present invention is to provide a method for preparing spindle-shaped agglomerate toughened boron carbide ceramics, comprising the following steps:

[0008] Towards SiC w The Ti powder is added to anhydrous ethanol, stirred at 60-80°C, and ground to obtain a mixed powder; the mixed powder is ball-milled with chloride salt powder to obtain a mixture, and the mixed powder is heated to 800-1200°C in an inert atmosphere and sintered once to obtain SiC containing a Ti3SiC2 coating through the reaction between the Ti powder and the surface of the silicon carbide whisker. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T);

[0009] The modified silicon carbide whiskers are mixed with boron carbide powder by ball milling, and the temperature is raised to 1600-1800° C. under vacuum conditions, and secondary sintering is performed. The Ti3SiC2 coating reacts with the boron carbide in situ, and agglomerates composed of TiB2 and SiC grains interlocked are introduced into the boron carbide ceramic to obtain spindle-shaped agglomerate toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0010] As a preferred embodiment, the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%.

[0011] As a preferred embodiment, the chloride salt, SiC w The molar ratio of Ti is 14-20:3-1:1.

[0012] As a preferred embodiment, the added amount of the modified silicon carbide whiskers is 2 to 20 wt % based on the mass of the boron carbide ceramic.

[0013] As a preferred embodiment, the chloride salt is KCl and / or NaCl.

[0014] As a preferred embodiment, during the primary sintering, in an argon atmosphere, the temperature is raised to 800-1200°C at 2-5°C / min, kept at this temperature for 20-40 minutes, then lowered to 400-600°C at 2-5°C / min, and cooled to room temperature with the furnace.

[0015] As a preferred embodiment, the secondary sintering adopts SPS sintering, specifically: heating to 1600-1800° C. at 50-150° C. / min, and keeping the temperature at 30-80 MPa sintering pressure for 5-15 minutes.

[0016] As a preferred embodiment, the vacuum degree is 5-50Pa.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention provides a spindle-shaped agglomerate toughened boron carbide ceramic and a preparation method thereof, wherein spindle-shaped agglomerates are distributed as toughening phases in boron carbide ceramics. The spindle-shaped agglomerates are interlocking structures of TiB2 and SiC particles, and the toughening mechanism thereof is as follows: First, the crack propagation diagram of the spindle-shaped agglomerate toughened boron carbide ceramic shows that there are obvious crack deflection and grain pullout phenomena inside the material. When the crack passes through the spindle-shaped agglomerate, it deflects between the SiC and TiB2 grains and eventually disappears inside the spindle. The crack continuously consumes the energy at the crack tip during the gradual deflection process, so the two interlocking grain structures inside the spindle significantly enhance the fracture toughness of the B4C ceramic. Second, the crack usually continues to propagate along the weak interface between the grains, and the mismatch of the thermal expansion coefficients of the two phases inside the matrix will cause obvious residual stress inside the matrix. Boron carbide (4.5×10 -6 K -1 ) has a thermal expansion coefficient similar to that of silicon carbide (4.35×10 -6 K -1 ) is similar to titanium boride (8.1×10 -6 K -1 ) have large differences in thermal expansion coefficients, which leads to large residual stresses at the TiB2 / B4C and TiB2 / SiC interfaces. When the crack passes through the TiB2 / B4C and TiB2 / SiC interfaces, crack deflection and microcrack toughening mechanisms will exist inside the sample.

[0019] (2) The present invention is to prepare the modified silicon carbide whisker (SiC w-T) introduced boron carbide (B4C) into ceramics, ultimately resulting in spindle-shaped TiB2-SiC agglomerates reinforced with unique structures. Through studies of the formation mechanism, microstructure, mechanical properties, and toughening mechanism of spindle-shaped TiB2-SiC agglomerates as a toughening phase, as well as system thermal stress simulations, it was concluded that two interlocking spindle-shaped TiB2-SiC agglomerates were successfully synthesized within the ceramic through an in-situ reaction between B4C and Ti3SiC2 coatings. When sintered at a temperature of only 1700°C, the B4C composite material achieved a relative density of 98.89±0.02%, a hardness of 32.89±1.67GPa, a flexural strength of 515±19MPa, and a maximum fracture toughness of 5.78±1.10MPa·m. 1 / 2 The shape and aspect ratio of TiB2-SiC agglomerates significantly affect the residual stress generated in the matrix, and the residual stress in the matrix increases significantly with the increase of the aspect ratio of the agglomerates. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD pattern of the spindle-shaped agglomerate toughened boron carbide ceramic prepared in Example 1 of the present invention;

[0021] Figure 2 These are SEM images of the spindle-shaped agglomerate-toughened boron carbide ceramics prepared in Example 1 of the present invention; (a) is 500 μm, and (b) is 20 μm;

[0022] Figure 3 Cross-sectional micromorphology and element distribution diagrams of the spindle-shaped agglomerate-toughened boron carbide ceramic prepared in Example 2 of the present invention; wherein, Figures (a) to (c) are cross-sectional micromorphology diagrams;

[0023] Figure 4 The cross-sectional SEM images of the silicon carbide whisker toughened boron carbide ceramic prepared in Comparative Example 1 of the present invention; wherein (a) is 500 μm, and (b) is 20 μm;

[0024] Figure 5 The cross-sectional SEM images and element distribution maps of the silicon carbide particle-toughened boron carbide ceramic prepared in Comparative Example 2 of the present invention are shown; wherein (a) to (d) are 20 μm, 5 μm, 2 μm, and 10 μm, respectively;

[0025] Figure 6 These are crack growth diagrams (toughening mechanism diagrams) of the polished surface of the spindle-shaped agglomerate-toughened boron carbide ceramic prepared in Example 1 of the present invention; wherein, (a) is 20 μm, and (b) is 10 μm. DETAILED DESCRIPTION

[0026] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention is further described below with reference to specific examples, but the examples are not intended to limit the present invention. The following experimental and detection methods are conventional methods unless otherwise specified; the reagents and raw materials are commercially available unless otherwise specified.

[0027] The present invention mentioned in the background technology that the thermal stability of whiskers is poor, which leads to poor strengthening and toughening effect of boron carbide ceramic matrix. w The reaction between the amorphous carbon on the surface generates in situ SiC coating to protect whiskers, which will introduce a large amount of residual silicon, thereby reducing the mechanical properties of the composite material. When the second phase is added for toughening, the ceramic material only has particle toughening and cannot introduce residual compressive stress to further improve the toughening effect of the composite ceramic material. Based on the above technical problems, the present invention provides a spindle-shaped agglomerate toughened boron carbide ceramic and a preparation method thereof. In the spindle-shaped agglomerate toughened boron carbide ceramic, spindle-shaped agglomerates are distributed in the boron carbide ceramic as a toughening phase. The spindle-shaped agglomerates are an interlocking structure of TiB2 and SiC particles, and the aspect ratio of the spindle-shaped agglomerate toughening phase is 3 to 15. The relative density of the spindle-shaped agglomerate toughened boron carbide ceramic is ≥96%, the Vickers hardness is 30 to 35 GPa, and the fracture toughness is 4 to 6 MPa·m 1 / 2 .

[0028] The technical solution of the present invention is analyzed and explained in detail below.

[0029] The present invention provides a method for preparing spindle-shaped agglomerate toughened boron carbide ceramics, comprising the following steps:

[0030] Towards SiC w The Ti powder is added to anhydrous ethanol, stirred at 60-80° C., and ground to obtain a mixed powder; the mixed powder is ball-milled with chloride salt powder to obtain a mixture, wherein the chloride salt can serve as a molten salt medium to transfer heat. During sintering, the chloride salt is converted into a molten state, which plays a better heat transfer role, thereby effectively reducing the synthesis temperature of the coating; the mixed powder is heated to 800-1200° C. in an inert atmosphere, and sintered once, and the Ti powder reacts with the surface of the silicon carbide whisker to obtain a SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-SiC whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0031] The modified silicon carbide whiskers are mixed with boron carbide powder by ball milling, and the temperature is raised to 1600-1800° C. under vacuum conditions, and secondary sintering is performed. The Ti3SiC2 coating reacts with the boron carbide in situ, and agglomerates composed of TiB2 and SiC grains interlocked are introduced into the boron carbide ceramic to obtain spindle-shaped agglomerate toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2). If the sintering temperature here is lower than 1600℃, the sintering will not be dense enough. If the sintering temperature exceeds 1800℃, the material will be over-burned, affecting the comprehensive performance of the composite material.

[0032] The present invention achieves the technical effects of toughening the boron carbide composite ceramic material by toughening the particles and introducing residual stress by introducing the modified silicon carbide whiskers into the boron carbide matrix.

[0033] In order to prepare a Ti3SiC2 coating of suitable thickness on the surface of silicon carbide whiskers, thereby providing better protection for the silicon carbide whiskers, the chloride salt, SiC w The molar ratio of Ti is 14-20:3-1:1.

[0034] To ensure uniform dispersion of silicon carbide whiskers within the boron carbide ceramic and achieve optimal toughening effects, the modified silicon carbide whiskers are added in an amount of 2 to 20 wt% based on the mass of the boron carbide ceramic. If the amount of modified silicon carbide whiskers added exceeds 20 wt%, not only will the manufacturing cost of the composite material increase, but it will also lead to poor dispersion of the toughening phase and agglomeration, which in turn reduces its toughening effect. If the amount of modified silicon carbide whiskers added to the boron carbide ceramic is less than 2 wt%, optimal toughening effects cannot be achieved.

[0035] In order to further achieve better heat transfer effect during the coating synthesis process, the chloride salt used in the present invention is KCl and / or NaCl. When the chloride salt is KCl and NaCl, KCl, NaCl, SiC w The molar ratio of Ti is 7 to 10:7 to 10:3 to 1:1.

[0036] To obtain spindle-shaped agglomerates with a better structure, the primary sintering process involves heating the material to 800-1200°C at a rate of 2-5°C / min in an argon atmosphere, holding the temperature for 20-40 minutes, then cooling it to 400-600°C at a rate of 2-5°C / min, and then cooling it to room temperature in the furnace. The secondary sintering process uses SPS sintering, specifically: heating the material to 1600-1800°C at a rate of 50-150°C / min, and holding the temperature at a sintering pressure of 30-80 MPa for 5-15 minutes. Because SPS sintering integrates plasma activation, hot pressing, and resistance heating, it utilizes bulk heating and surface activation to achieve ultra-rapid densification sintering of the material, resulting in a fast heating rate, short sintering time, low sintering temperature, and uniform grain size, which is beneficial for controlling the fine structure and high density of the sintered body. Furthermore, the low sintering temperature and short holding time of SPS sintering can reduce the effects of high temperatures on the thermal stability of silicon carbide whiskers.

[0037] It should be noted that the vacuum degree is 5 to 50 Pa. If the vacuum degree is too low, the whiskers, Ti3SiC2 coating and boron carbide will be highly oxidized. If the vacuum degree is too high, on the one hand, it is difficult to implement the instrument and requires higher vacuum equipment, and on the other hand, it significantly increases the manufacturing cost of the composite ceramic material.

[0038] The technical effects of the present invention are described below through specific embodiments and comparative examples.

[0039] Example 1

[0040] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0041] According to KCl, NaCl, SiC w With a molar ratio of 10:10:2:1 to SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 70 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1100 ° C at 4 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 500 ° C at 4 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0042] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 9wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 5Pa, and the temperature was raised to 1700℃ at a rate of 100℃ / min. The mixture was kept at a sintering pressure of 50MPa for 10min. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0043] Example 2

[0044] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0045] According to KCl, NaCl, SiC w With a molar ratio of 7:7:1:1 to SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 60 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 800 ° C at 2 ° C / min in an argon atmosphere, kept warm for 20 minutes, and then cooled to 400 ° C at 2 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0046] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 10 wt % of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 5 Pa, and the temperature was raised to 1600 ° C. at a rate of 50 ° C. / min. The mixture was kept at a sintering pressure of 30 MPa for 5 minutes. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0047] Example 3

[0048] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0049] According to KCl, NaCl, SiC wThe molar ratio of Ti is 7:10:3:1, and the SiC w The Ti powder and the Ti powder were added with anhydrous ethanol, stirred at 80°C, and ground to obtain a mixed powder; the NaCl powder and the KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1200°C at 5°C / min in an argon atmosphere, kept warm for 40 minutes, and then cooled to 600°C at 5°C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain a SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0050] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 20 wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 50 Pa, and the temperature was raised to 1800 ° C at a rate of 150 ° C / min. The mixture was kept at a sintering pressure of 80 MPa for 15 minutes. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0051] Example 4

[0052] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0053] According to KCl, NaCl, SiC w The molar ratio of Ti is 10:7:2:1, and the SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 70 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1100 ° C at 4 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 500 ° C at 4 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0054] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 2 wt % of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 20 Pa, and the temperature was raised to 1700 ° C. at a rate of 100 ° C. / min. The mixture was kept at a sintering pressure of 50 MPa for 10 minutes. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0055] Example 5

[0056] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0057] According to KCl, NaCl, SiC w The molar ratio of Ti is 7:10:2:1, and the SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 60 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1000 ° C at 4 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 400 ° C at 4 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0058] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 9wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 10 Pa, and the temperature was raised to 1700° C. at a rate of 100° C. / min. The mixture was kept at a sintering pressure of 50 MPa for 10 min. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0059] Example 6

[0060] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0061] According to KCl, NaCl, SiC w With a molar ratio of 10:10:2:1 to SiC w The mixture was heated to 1200°C at a rate of 2°C / min in an argon atmosphere, kept at that temperature for 30 minutes, and then cooled to 600°C at a rate of 2°C / min, and cooled to room temperature in the furnace. The Ti powder reacted with the surface of the silicon carbide whisker to obtain a SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0062] The modified silicon carbide whiskers were ball-milled and mixed with boron carbide powder, with the addition amount of the modified silicon carbide whiskers being 15 wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum degree of 10 Pa, with the temperature raised to 1700 ° C. at a rate of 100 ° C. / min, and kept at a sintering pressure of 50 MPa for 10 min. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0063] Example 7

[0064] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0065] According to KCl, NaCl, SiC w The molar ratio of Ti is 7:8:1:1, and the SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 70 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1100 ° C at 4 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 500 ° C at 4 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w-T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0066] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 9wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 10 Pa, and the temperature was raised to 1700° C. at a rate of 100° C. / min. The mixture was kept at a sintering pressure of 50 MPa for 10 min. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0067] Example 8

[0068] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0069] According to KCl, NaCl, SiC w The molar ratio of Ti is 10:8:3:1, and the SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 70 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1000 ° C at 3 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 500 ° C at 3 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0070] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 9wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 10 Pa, and the temperature was raised to 1600° C. at a rate of 100° C. / min. The mixture was kept at a sintering pressure of 60 MPa for 8 minutes. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0071] In order to further illustrate the technical effects of the present invention, the present invention also provides a comparative example, which is as follows:

[0072] Comparative Example 1

[0073] Compared with Example 1, the difference is that the silicon carbide whiskers are not modified.

[0074] A method for preparing silicon carbide whisker toughened boron carbide ceramics comprises the following steps:

[0075] Silicon carbide whiskers and boron carbide powder were ball-milled and mixed, wherein the amount of silicon carbide whiskers added was 9wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 10 Pa, and the temperature was increased to 1700°C at a rate of 100°C / min. The mixture was sintered at a pressure of 50 MPa for 10 min to obtain silicon carbide whisker toughened boron carbide ceramic (B4C-SiC w ).

[0076] Comparative Example 2

[0077] Compared with Example 1, the silicon carbide particles SiC p , rather than silicon carbide whiskers.

[0078] B4C-SiC p Preparation of Ti3SiC2 ceramics: B4C-SiC prepared in Example 1 of the present invention w B4C-SiC / Ti3SiC2 ceramics were prepared by the process of p / Ti3SiC2 ceramics for comparison of micromorphology and mechanical properties.

[0079] A method for preparing silicon carbide particle-toughened boron carbide ceramics comprises the following steps:

[0080] According to KCl, NaCl, SiC p With a molar ratio of 10:10:2:1 to SiC p The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 70 ° C, and ground to obtain a mixed powder; the NaCl powder and the KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1100 ° C at 4 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 500 ° C at 4 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide particles to obtain SiC containing Ti3SiC2 coating. p , and obtain modified silicon carbide particles (SiC p -Ti3SiC2, also known as SiC p -T);

[0081] The modified silicon carbide particles were mixed with boron carbide powder by ball milling. The amount of the modified silicon carbide particles added was 9 wt% of the mass of the boron carbide ceramic. The modified silicon carbide particles were sintered by SPS at a vacuum of 10 Pa, and the temperature was increased to 1700 ° C at a rate of 100 ° C / min. The temperature was kept at a sintering pressure of 50 MPa for 10 minutes. The Ti3SiC2 coating reacted with the boron carbide in situ to obtain silicon carbide particle toughened boron carbide ceramic (B4C-SiC p / Ti3SiC2).

[0082] Comparative Example 3

[0083] Compared with Example 1, the difference is that the addition amount of the modified silicon carbide whiskers is reduced from 9 wt % to 1 wt %.

[0084] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0085] According to KCl, NaCl, SiC w With a molar ratio of 10:10:2:1 to SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 70 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1100 ° C at 4 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 500 ° C at 4 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0086] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling. The amount of the modified silicon carbide whiskers added was 1 wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 5 Pa, and the temperature was raised to 1700 ° C at a rate of 100 ° C / min. The mixture was kept at a sintering pressure of 50 MPa for 10 minutes. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0087] Comparative Example 4

[0088] Compared with Example 1, the difference is that the addition amount of modified silicon carbide whiskers is increased from 9 wt % to 25 wt %.

[0089] A method for preparing spindle-shaped agglomerate toughened boron carbide ceramics comprises the following steps:

[0090] According to KCl, NaCl, SiC w With a molar ratio of 10:10:2:1 to SiC w The Ti powder and the KCl powder were added to anhydrous ethanol, stirred at 70 ° C, and ground to obtain a mixed powder; NaCl powder and KCl powder were ball-milled to obtain a mixed salt; the mixed powder and the mixed salt were ball-milled to obtain a mixture, the mixed powder was heated to 1100 ° C at 4 ° C / min in an argon atmosphere, kept warm for 30 minutes, and then cooled to 500 ° C at 4 ° C / min, and cooled to room temperature with the furnace, and the Ti powder reacted with the surface of the silicon carbide whisker to obtain SiC containing Ti3SiC2 coating. w , and obtain modified silicon carbide whiskers (SiC w -Ti3SiC2, also known as SiC w -T), the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100 to 600 nm, a length of 10 to 50 μm, and a metal impurity content of <1 wt%;

[0091] The modified silicon carbide whiskers were mixed with boron carbide powder by ball milling, wherein the amount of the modified silicon carbide whiskers added was 25 wt% of the mass of the boron carbide ceramic. The mixture was sintered by SPS at a vacuum of 5 Pa, and the temperature was raised to 1700 ° C. at a rate of 100 ° C. / min. The mixture was kept at a sintering pressure of 50 MPa for 10 minutes. The Ti3SiC2 coating reacted with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked were introduced into the boron carbide ceramic to obtain spindle-shaped agglomerates toughened boron carbide ceramics (B4C-SiC w / Ti3SiC2).

[0092] The properties of the spindle-shaped agglomerate toughened boron carbide ceramics obtained in Examples 1 to 8 of the present invention and the materials prepared in Comparative Examples 1 to 4 were tested, and the specific test results are as follows.

[0093] Depend on Figure 1 It can be seen that the main phases of the mixed powder are B4C, Ti3SiC2 and β-SiC. After spark plasma sintering at 1700℃ for 10 minutes, the phases of the composite material are B4C, TiB2, SiC and C respectively.

[0094] In order to further determine the B4C-SiC w The densification temperature of the B4C composite material is as follows: Figure 2 As shown in Figure 2, there are a large number of closed pores in the cross section of the composite material prepared at 1600℃, as shown in Figure 2. Figure 3As shown in Figure 2, the increase in temperature significantly densifies the internal structure of the material, and no obvious pores exist in the cross section. Spindle-shaped agglomerates are uniformly dispersed in the B4C matrix as the second phase, with a size of 30μm to 130μm, as shown in Figure 2. Figure 2 As shown, the B4C matrix clearly fractures primarily through transgranular fracture, while the TiB2-SiC agglomerates fracture primarily through intergranular fracture. The spindle structure of the second phase is primarily composed of interlocking TiB2 and SiC grains, with grain sizes ranging from 0.5μm to 3μm. The high-contrast white phase is TiB2, while the low-contrast gray phase is SiC.

[0095] Depend on Figure 4 It can be seen that B4C-SiC sintered at 1700℃ w There are obvious pores inside the cross section of the ceramic. w It is degraded into particles dispersed in the B4C matrix. After testing, the density of the sample is only 82.23%. w The hardness and bending strength of ceramics are 24.02±1.34GPa and 425±50MPa. w The presence of does not reduce the sintering densification temperature of B4C ceramics. w In the Ti3SiC2 / Ti3SiC2 composite material, the Ti3SiC2 coating reacts with the B4C matrix in situ to form TiB2 and SiC phases, which reduces the sintering densification temperature of the system and effectively promotes the densification of B4C ceramics. w The hardness of the / Ti3SiC2 composite material is 32.89±1.67GPa; the flexural strength is 515±19MPa, and the fracture toughness is 5.78±1.10MPa·m 1 / 2 , which are significantly higher than B4C-SiC w The fine grains (TiB2 and SiC) formed by the in-situ reaction are beneficial to improving the hardness and bending strength of the matrix material, while the new spindle-shaped agglomerate morphology improves the fracture toughness of the material.

[0096] In Comparative Example 2, the prepared SiC p -T was introduced into the B4C matrix and the B4C-9wt%SiC was sintered at 1700℃ p / Ti3SiC2 composite material cross-section SEM analysis, such as Figure 5 As shown, no TiB2-SiC aggregates were observed within the cross-section of the material. The TiB2 and SiC particles were uniformly dispersed within the matrix. Testing revealed a relative density of 94.02%, indicating incomplete densification. This indicates that spherical aggregates cannot be produced using similar methods.

[0097] In order to study the toughening mechanism of spindle-shaped TiB2-SiC aggregates in B4C ceramics, the micromorphology of the polished surface and fracture surface of the sample prepared in Example 1 were observed respectively. Figure 6 From the crack propagation diagram of the polished surface of the sample, it can be seen that obvious crack deflection and grain pullout phenomena are observed inside the sample. When the crack passes through the spindle-shaped agglomerate, it deflects between the SiC and TiB2 grains and eventually disappears inside the spindle. The crack will continuously consume the energy at the crack tip during the gradual deflection process. Therefore, the two interlocking grain structures inside the spindle significantly enhance the fracture toughness of B4C ceramics. Generally, cracks usually continue to propagate along the weak interface between the grains. The mismatch of the thermal expansion coefficients of the two phases inside the matrix will cause obvious residual stress inside the matrix. Boron carbide (4.5×10 -6 K -1 ) has a thermal expansion coefficient similar to that of silicon carbide (4.35×10 -6 K -1 ) is similar to titanium boride (8.1×10 -6 K -1 The large difference in thermal expansion coefficients between TiB2 / B4C and TiB2 / SiC results in large residual stresses at the TiB2 / B4C and TiB2 / SiC interfaces. When a crack penetrates the TiB2 / B4C and TiB2 / SiC interfaces, crack deflection and microcrack toughening mechanisms occur within the sample.

[0098] Therefore, the special spindle-shaped aggregate structure and the mismatch of thermal expansion coefficients between the phases are the main factors leading to the improvement of the fracture toughness of the system. The thermal expansion mismatch stress P at the interface can be calculated according to formula (1).

[0099]

[0100] Where m and p represent the matrix B4C and the second phase (TiB2 or SiC), Δα=α p -α m 、ν m and ν p is Poisson's ratio, E m and E p The Young's modulus of the matrix B4C and the second phase (TiB2 or SiC) are respectively. At ΔT = 1973-298K = 1675K, the micro-residual stress P value caused by the different thermal expansion coefficients of B4C and TiB2 is 2640MPa. Similarly, the calculated P value of SiC and TiB2 is 2665MPa.

[0101] In summary, the present invention is to modify silicon carbide whiskers (SiC wThe researchers introduced boron carbide (B4C) into TiB2-SiC ceramics, ultimately yielding spindle-shaped TiB2-SiC agglomerates with a unique structure. The dual toughening approach of introducing whiskers and residual compressive stress into the ceramic matrix significantly enhanced the toughening effect of the boron carbide ceramics.

[0102] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A spindle-shaped agglomerate toughened boron carbide ceramic, characterized in that: The spindle-shaped agglomerates are distributed in the boron carbide ceramic as a toughening phase, the spindle-shaped agglomerates are interlocking structures of TiB2 and SiC particles, and the aspect ratio of the spindle-shaped agglomerates is 3 to 15; The method for preparing the spindle-shaped agglomerate toughened boron carbide ceramic comprises the following steps: Towards SiC w The Ti powder and ethanol are added, stirred at 60-80°C, and ground to obtain a mixed powder; the mixed powder is ball-milled with chloride salt powder to obtain a mixture, and the mixed powder is heated to 800-1200°C in an inert atmosphere and sintered once to obtain SiC containing Ti3SiC2 coating through the reaction between Ti powder and the surface of silicon carbide whiskers. w , obtaining modified silicon carbide whiskers; the silicon carbide whiskers are β-silicon carbide whiskers with an average diameter of 100~600 nm, a length of 10~50μm, and a metal impurity content of <1wt%; the chloride salt, SiC w The molar ratio of Ti is 14~20:3~1:1; The modified silicon carbide whiskers are mixed with boron carbide powder by ball milling, and the temperature is raised to 1600-1800° C. under vacuum conditions, and secondary sintering is performed. The Ti3SiC2 coating reacts with the boron carbide in situ, and agglomerates of TiB2 and SiC grains interlocked are introduced into the boron carbide ceramic to obtain spindle-shaped agglomerate-toughened boron carbide ceramic. The added amount of the modified silicon carbide whiskers is 2-20 wt% based on the mass of the boron carbide ceramic.

2. The spindle-shaped agglomerate toughened boron carbide ceramic according to claim 1, characterized in that: The chloride salt is KCl and / or NaCl.

3. The spindle-shaped agglomerate toughened boron carbide ceramic according to claim 1, characterized in that: During the primary sintering, the temperature is raised to 800-1200°C at a rate of 2-5°C / min under an argon atmosphere, kept at this temperature for 20-40 minutes, then lowered to 400-600°C at a rate of 2-5°C / min, and cooled to room temperature in the furnace.

4. The spindle-shaped agglomerate toughened boron carbide ceramic according to claim 1, characterized in that: The secondary sintering adopts SPS sintering, specifically: heating to 1600-1800° C. at 50-150° C. / min, and keeping the temperature at 30-80 MPa sintering pressure for 5-15 minutes.

5. The spindle-shaped agglomerate toughened boron carbide ceramic according to claim 1, characterized in that: The vacuum degree of the vacuum is 5~50Pa.

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