Effect of sintering temperature and TiB2 content on the grain size of B4C-TiB2 composites

Journal Pre-proof Effect of sintering temperature and TiB2 content on the grain size of B4 C-TiB2 composites Yingying Liu (Data curation) (Writing - original draft), Zhenqin Li (Software), Yusi Peng (Software), Yihua Huang (Formal analysis) (Investigation) (Conceptualization), Zhengren Huang (Validation), Deku Zhang (Project administration)

PII:

S2352-4928(19)31051-7

DOI:

https://doi.org/10.1016/j.mtcomm.2019.100875

Reference:

MTCOMM 100875

To appear in:

Materials Today Communications

Received Date:

9 October 2019

Revised Date:

19 December 2019

Accepted Date:

23 December 2019

Please cite this article as: Liu Y, Li Z, Peng Y, Huang Y, Huang Z, Zhang D, Effect of sintering temperature and TiB2 content on the grain size of B4 C-TiB2 composites, Materials Today Communications (2019), doi: https://doi.org/10.1016/j.mtcomm.2019.100875

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Effect of sintering temperature and TiB2 content on the grain size of B4C-TiB2 composites

Yingying Liu a, b, Zhenqin Lia,b, Yusi Penga,b, Yihua Huang a, * [email protected], Zhengren Huang a, * [email protected], Deku Zhang c, * [email protected]

a

. State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of

Ceramics, Chinese Academy of Sciences, Shanghai 201800, No. 588, HeShuo Road, Jiading District, Shanghai, China b

. University of Chinese Academy of Sciences, Beijing 100049, China

*

School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094

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c.

Corresponding author: (Z. Huang), (Y. Huang), (D. Zhang)

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Highlights

Preparation of B4C-TiB2 composite by adding TiB2 to improve the fracture toughness of B4C while maintaining high hardness.

The main mechanism of the TiB2 phase toughening B4C ceramic is crack deflection as a

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result of the differences in their thermal expansion coefficients. The analysis of grain size distribution by electron backscattered diffraction (EBSD) shows

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that the pinning effect of TiB2 can refine B4C grain. 

Dislocations are observed in the TEM image of the B4C-TiB2 composite, which also

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improves the hardness and toughness of the material.

ABSTRACT

Boron carbide (B4C) is a ceramic with great properties such as low density, the third hardness after diamond and cubic BN. However, it is a limited use cause of its poor sinterability and low fracture toughness. Titanium diboride (TiB2) has been used as an ideal additive to get B4C ceramics with good properties. B4C-TiB2 composites were prepared by spark plasma sintering (SPS) at 1950℃ under a pressure of 50 MPa, using TiB2 and B4C powder

mixture as starting materials. The effect of TiB2 content on the mechanical performance and grain size of B4C-TiB2 composites was investigated. The B4C-TiB2 composites with 20 mol% TiB2 addition show great comprehensive properties, the relative density of 97.91%, a Vickers hardness of 29.82 ± 0.14 GPa, and fracture toughness of 3.70 ± 0.08 MPa·m1/2 respectively. The results indicated that as the TiB2 content increase, the hardness of the composite decreases and the fracture toughness increases. The main mechanism of the TiB2 phase toughening B4C ceramic is crack deflection as a result of the differences in their thermal expansion coefficients. The analysis of grain size distribution by electron backscattered diffraction (EBSD) shows that the pinning effect of TiB2 can refine B4C grain. The pinning effect is another reason for the high hardness and high toughness of the B4C-TiB2 composites.

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Dislocations are observed in the TEM image of the composite, which also improves the hardness and toughness of the material.

Keywords: spark plasma sintering, B4C-TiB2 composites, grain size, mechanical performance, pining effect

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1.Introduction

Boron carbide (B4C) has outstanding physicochemical performance, such as high melting point,

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low density, superior hardness, high thermal conductivity, and large neutron absorption surface[1-3].

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B4C is candidate materials for wear-resistant components, cutting tools, lightweight armor products and neutron radiation shielding, etc [4, 5]. However, B4C suffers from low sinterability (due to the strong B-C covalently bond and the B2O3 oxide layer) and poor fracture toughness[6, 7]. B4C

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ceramics fabricated by pressureless sintering requires high sintering temperature, long holding time, and sintering aids[8, 9]. So various sintering additives were added to improve the densification of

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B4C, such as Al2O3[10], Fe[11], Si[12]. Spark plasma sintering (SPS) attracting the attention of many researchers because it can be used for various materials to full density without additions. Boron

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carbide ceramics with fine grain and excellent properties were prepared by SPS to have been reported[13-15].

The addition of the second phase is one of the effective toughening methods. Boride is the ideal

toughening phase of B4C ceramics due to its high melting point and high hardness. Titanium boride (TiB2) additions to B4C are beneficial for both densification and fracture toughness. Moreover, no chemical reaction occurs between B4C and TiB2[16]. As observed by Xu et al. [17], 2.8 vol% TiB2 in B4C reduced the porosity of B4C ceramic to less than 2% after spark plasma sintering at 1800℃ with

a hardness of 31.6 GPa. In a study of the B4C-TiB2 composite [18], additions of 20 vol% TiB2 improved the relative density to 99.9% and the toughness from 1.8 to 3.3 MPa·m1/2 after spark plasma sintering at 2000℃. The fined-grained B4C-TiB2 composites fabricated via in-situ reactive routes. He et al.[19] prepared B4C-TiB2 composites with Ti3SiC2 and B4C as starting materials by reaction hot pressing. 10 wt% Ti3SiC2 in B4C shows excellent mechanical performances, the hardness and toughness are 3163 kg/mm2 and 7.01 MPa·m1/2, respectively. In this work, B4C-TiB2 composites were prepared via spark plasma sintering (SPS) using B4C and TiB2 powders mixture as starting materials. The fracture toughness of B4C-TiB2 composites is

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significantly improved while maintaining a high hardness. The influences of sintering temperature and TiB2 content on the relative density and mechanical performances of B4C-TiB2 composites were studied. The present work focused on the microstructure of the composites, especially the grain size.

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The toughening mechanism of the TiB2 particle and the relationship between microstructure and mechanical properties were discussed.

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2.Materials and methods 2.1Materials

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The raw materials adopted were commercial B4C and TiB2 powders. The B4C powder with a d90 size of 2.10 μm and the TiB2 powder is 3.72 μm in d90 size. The particle size distribution of the raw

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materials is illustrated in Fig.1. The morphologies and XRD images of B4C and TiB2 powders are shown in Fig.2. The Characteristics of B4C and TiB2 powders are listed in Table 1. Commercially available B4C and TiB2 powders were balls mixed in ethanol for 24h using SiC

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beads with a rotary speed of 300 rpm. The molar ratio of B4C/TiB2 was set as 95:5, 90:10, 80:20 and 70:30 respectively. After mixing, the slurry was dried at blast drying oven at 90 °C for 24 hours. The

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dried powder mixtures were passed a 200 mesh sieve to minimize segregation and agglomeration. The scanning electron micrographs of the B4C-TiB2 powder mixtures are shown in Fig.3. The powder mixtures with different contents (5, 10, 20, 30 mol%) of TiB2 are prepared and their nomenclatures are B05, B10, B20, B30 in turn (Table 2). 2.2 SPS experiments The B4C-TiB2 powder mixture was placed in a graphite mold having an inner diameter of 20

mm. A graphite sheet was placed between the powder and the mold to facilitate demolding. Then place the mold in the SPS chamber and set up the program. The selected pressure, sintering temperature, holding time and heating rate was 50 MPa, 1800-2000℃, 10 min, 100℃/min, respectively. Wait for cooling to room temperature and take out the sintered sample. 2.3 Characterization The sintered samples were simply machined then polished to 0.5μm using a diamond polishing solution. The microstructure of the B4C-TiB2 composites was characterized using SEM and TEM. The crystalline phases in B4C-TiB2 composites were analyzed by XRD. The grain sizes of the B4C

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and TiB2 and the two-phase distribution in the composites were characterized by electron backscattered diffraction (EBSD). 2.4 Mechanical testing

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The densities of the B4C-TiB2 composites were calculated by the Archimedes method in

deionized water. The theoretical density of the composites was calculated by the regulation of the

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mixture. The densities of B4C and TiB2 were taken as 2.52 and 4.68 g cm-3 (including Zr content), respectively.

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To measure the hardness of the composites, the samples were polished with diamond pastedown to 0.5 μm. The hardness of the B4C-TiB2 composites was tested by a Vickers hardness tester, and the

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load is 1 kg for 10 seconds. The fracture toughness of the B4C-TiB2 composites was based on the Vickers indentation method. The toughness was determined by the crack length of hardness indentation. The formula for calculating fracture toughness by the indentation method is:

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𝐾𝐼𝐶 = 0.16𝐻𝑣 𝑎2 𝑐 −1.5 [38]

where KIC is fracture toughness, HV is hardness, a is the impression radius, c is the indentation crack

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length. The final hardness and fracture toughness is the average of six measurements. 3.Results and discussion 3.1 Micro-morphology of the powder mixture Fig.3(a)-(d) shows the microstructure of powder mixtures with different contents of TiB2. The dark phase is B4C particles. The white phase is TiB2 particles. The TiB2 particles were uniformly distributed in the B4C matrix, as shown in Fig.3 (a)-(c). Increase the TiB2 content to 30 mol%,

agglomeration of the TiB2 particles can be observed in Fig.3 (d). This indicates that aggregation and agglomeration occur when the TiB2 content is excessive, which is mainly due to the large difference in theoretical density between B4C and TiB2. 3.2 Mechanical properties The influences of sintering temperature on relative density and Vickers hardness of B20 is shown in Fig.4. The relative density and hardness increase as the sintering temperature increase. The maximum relative density of 97.91% obtained at 1950℃. The maximum value of the hardness of the composites reaches 29.82 ± 0.14 GPa when the sintering temperature is 1950℃. In general, the

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hardness of a material is determined by the nature and density of itself. When other conditions are determined, the hardness increases as the density increases[17]. The relative density, hardness of the composites sintered at different temperatures are listed in Table 3. Fig.5 shows the relationship

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between the TiB2 content and the relative density of the B4C-TiB2 composite sintered at 1950 °C. The content of TiB2 increases from 0 mol% to 30 mol%, the relative density increase to a maximum

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at 5 mol% then decreases. The TiB2 content is between 0 mol% to 20 mol%, all of the relative densities of the composites are around 98%. When the TiB2 content is 5 mol%, the relative density of

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the composite reaches the maximum, 98.71%. With 5 mol%, the addition of TiB2 can promote the densification of B4C ceramics through the reaction between TiB2 and B2O3[17]. As the TiB2 content

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is 30 mol%, the relative density of the composite drop dramatically, the main reason is that the TiB2 ceramic has poor sinterability. The relative density of pure TiB2 ceramic only 96.71% after sintered by SPS at 2000℃ under 60 MPa[20].

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The relative density, hardness, toughness of the composites with varies TiB2 content are listed in Table 4. Fig.6 shows the fracture toughness and Vickers hardness of B4C-TiB2 composite with

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different molar fractions of TiB2. As observed, hardness decrease from 31.91 ± 0.72 GPa to 28.86 ± 0.29 GPa as the content of the TiB2 increase from 0 mol% to 30 mol%. The toughness increased from 2.62 ± 0.1 to 4.36 ± 0.1 MPa·m1/2 as the TiB2 content increase from 0 mol% to 30 mol%. Yue et al.[21] used the starting materials of B4C, TiCl4, and C to fabricated B4C-TiB2 composites by hot press. The composite with 43 wt.% (about 37.5 mol%) TiB2 shows great properties and a relative density of 99.8%, toughness of 9.4 MPa·m1/2, a flexural strength of 506 MPa, as well as Vickers

hardness of 23.6 GPa. Similar results were reported in another article based on B4C, TiO2 and phenolic resin[22]. Although the fracture toughness of the B4C-TiB2 composite synthesized by in-situ reaction sintering is greatly improved, the excessive addition of TiB2 causes a remarkable decrease in hardness. In this experiment, the toughness of B4C ceramics is effectively improved while maintaining high hardness. The addition of the TiB2 phase can toughen B4C ceramic but reduce the hardness. This is consistent with related reports[23-25]. 3.3 Phase composition The XRD image of the composite is shown in Fig.7. Fig.7 (a) shows the B4C-TiB2 composites

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with 20 mol% TiB2 sintered at different temperatures. The main phases are the B4C and TiB2 phase. There is a small peak in the XRD pattern, which is analyzed to be the peak of SiC. It shows that the powder mixtures contain a small amount of SiC, which is mainly caused by the use of SiC balls

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when mixing. Fig.7 (b) shown the B4C-TiB2 composites with different content of TiB2 sintered at 1950℃. As TiB2 content increases, characteristic diffraction peaks of B4C becomes lower,

3.4 Microstructures of sintered samples

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characteristic diffraction peaks of TiB2 becomes higher.

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The SEM patterns of the polished surface of the B20 sintered at different temperatures are illustrated in Fig.8. In these images, the black continuous phase is identified as the B4C matrix,

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whereas the white phase is TiB2. It is apparent that there are many pores in the B20 sintered at a temperature below 1950℃. No pores are observed on the surface of the B20 sintered at 1950℃, indicating that the composites are almost dense (their porosities ‹2%), as shown in Fig.8 (d).

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The surfaces of composites with varies TiB2 content are illustrated in Fig.9 (a)-(d). All composites were fabricated by SPS at 1950℃. Fig.9 (e)-(g) confirm the phase distribution. The white

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species in these typical backscattered electron images are verified as TiB2, whereas the black continuous phase is B4C. The energy spectrum results in the gray area indicate that its main elements are B, C, Si, Zr, and Ti. Among them, Si is mainly introduced due to the use of SiC ball in the mixing process, and Zr is an impurity in TiB2 raw material powder. Therefore, the main phase in the gray area is SiC. No residual pores can be observed in B4C-TiB2 composites. The content of TiB2 is between 5 mol% to 20 mol%, the TiB2 particles are small and uniformly dispersed in the B4C matrix.

As the TiB2 content increase to 30 mol%, some large TiB2 particles are detected. The grain begins to coarsen as the TiB2 content increases. To better understand the effect of TiB2 addition on the mechanical performance, the fracture surfaces of the B20 are shown in Fig.10 (a). It is apparent that the fracture surface of B4C particles is smooth and flat, whereas the TiB2 is rough and uneven. The image indicates that the transcrystalline fracture mainly occurred within the B4C particles, while intergranular mainly existed along the boundary of TiB2 grain. The same conclusion was reported by other researchers[26-28]. The SEM image of crack propagation paths of the B4C-TiB2 composites after Vickers hardness indentation is illustrated in Fig.10 (b). According to the image, it can be

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known that transgranular cracks are happened in the B4C phase, while the cracks mainly propagate intergtanularly along the grain boundaries between B4C and TiB2. The reason for crack deflection is the large difference in thermal expansion between B4C (4.5×10-6K-1[29]) and TiB2 (8.1×10-6K-1[30]).

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The crack deflection is one of the causes of TiB2 toughening B4C[18].

Fig.11 shows the TEM image of the B20 and electron diffraction patterns. There are two kinds

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of electron diffraction patterns, Fig.11-1 was in accordance with the [0 1 0] area axis diffraction mottling of B4C, Fig.11-2 was identical with the [0 1 0] area axis diffraction mottling of TiB2. As

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observed in Fig.11b the phase difference between the two sides of the grain boundary can be clearly distinguished. The grain boundaries of B4C-TiB2 clear and very narrow indicating that B4C and TiB2

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have good interfacial compatibility and no interfacial reaction. This provides the necessary conditions for the good performance of the B4C-TiB2 composite. And dislocations were seen in the grains of B4C and TiB2. When cracks reach the area in the composite with dislocations, nano crack

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nuclei of the crack will be generating due to the immovable dislocation in the composites. The front process zone (FPZ) is expanded therefore the fracture toughness and hardness of the composites are

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enhanced. The dislocation sub-boundaries enhance the fracture toughness of the poly-crystals of Al2O3 and Si3N4 was observed by Moon et al [31]. Awaji et al.[32] analyzed the toughening and strengthening of the dislocations around the second phase particles on Al2O3/SiC and Si3N4/SiC nanocomposites based on Griffith energy equilibrium. 3.5 Phase composition and grain size of the sample by EBSD Electron backscattered diffraction (EBSD) is a powerful technique that determines the phase

composition, crystallographic orientation, and grain size measurement and so on. It can be used in a variety of materials, such as semiconductors, metals, minerals, and ceramics[33-35]. The phase composition and distribution of the B4C-TiB2 composites are shown in Fig.12. There are only two phases in the composite, the red phase is the B4C matrix, the green is identified as the TiB2 phase. That is consistent with the results of phase analysis by XRD. As observed, the TiB2 grains uniformly distributed in the B4C matrix. As the content of TiB2 increases, the grain refinement of B4C and the grain coarsening of TiB2 The grain orientation of composites with different TiB2 content as indicated by the EBSD map as shown in Fig.12. Different grain orientations are represented by different

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colors. All composites are fine equiaxed grains rather than coarse dendrites. No significant grain orientation was observed.

The average grain size of the B4C and TiB2 phase in the B4C-TiB2 composites are listed in Table

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5. The grain size distribution of B4C in the B4C-TiB2 composites is illustrated in Fig.14.Most of the grain size of pure B4C ceramic is between 0.5 μm to 4 μm. The TiB2 content increase to 10 mol%,

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most of the grain size of B4C in the composite is between 0.5 μm to 3.5 μm. Continue increasing the TiB2 content to 20 mol% and 30 mol%, the grain size distribution of B4C is more concentrated,

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mainly distributed between 0.5 μm to 3 μm. The frequency of TiB2 grain size between 3 and 4 μm in composites with TiB2 content of 0 and 5 mol% is significantly higher than that of 10mol%, 20mol%

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and 30 mol% TiB2 content. The grain size of B4C decreases with the TiB2 content increase. Fig.15 shows the grain size distribution of TiB2 in the B4C-TiB2 composites. When the TiB2 content is 5 mol%, the grain size of TiB2 mainly distributed between 0.5 μm to 1.5 μm, and no grain size greater

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than 3 μm was observed. The content of TiB2 is 10 mol%, 20 mol% and 30 mol%, the grain size of TiB2 mainly distributed between 0.5 to 2.5 μm, 0.5 to 3.0 μm, and 0.5 to 3.5 μm, respectively. As

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TiB2 content increase, the TiB2 grain grow. The growth of TiB2 grains in B4C-TiB2 composites has been reported in other work[36]. The effect of TiB2 content on the average grain size of B4C and TiB2 is summarized in Fig.16.

As the TiB2 content increase from 0 to 30 mol%, the average grain size of TiB2 increase from 1.14 μm to 1.45 μm, increase by 27%. As TiB2 content increases from 0 to 30 mol%, the average grain size of B4C decreases from 1.91 μm to 1.67 μm (reduces by 12.6%). (as a whole) When the content

of TiB2 is 20 mol%, the uniformity of the mixture decreases due to the aggregation of TiB2 powder, which causes the B4C grain size to increase slightly. The reason for the B4C grain size decrease is that the pinning effect of the TiB2 particle. The TiB2 grain distribution around the B4C grains effectively hinders the slip of the B4C grain boundary and refines the B4C grain. The pinning effect of the second phase has been reported in other studies[20, 37]. 4. Conclusions B4C ceramics have broad application prospects due to its low density, superior hardness, high melting point, and other outstanding properties. However, low self-diffusion and poor sinterability,

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and the lower fracture toughness limit its widespread applications. The addition of TiB2 can

effectively improve the toughness of B4C ceramic while maintaining high hardness. In this work, B4C-TiB2 composites were fabricated by spark plasma sintering at 1950℃ under a pressure of 50

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MPa, using B4C and TiB2 powder mixture. The B4C-TiB2 composites with 20 mol% TiB2 addition show great properties, the relative density of 97.91%, a Vickers hardness of 29.82 ± 0.14 GPa, and

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toughness of 3.70 ± 0.08 MPa·m1/2 respectively. The effect of TiB2 content on the mechanical properties and grain size of B4C-TiB2 composites was investigated. The results indicated that as the

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TiB2 content increase, the hardness of the composite decreases the fracture toughness increases. The analysis of grain size distribution by EBSD shows that the pinning effect of the TiB2 particle can refine B4C grain. The average grain size of B4C in B4C-TiB2 composites decreases from 1.91 μm for

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pure B4C ceramic to 1.67μm for the 30 mol% TiB2 composites. The main mechanism of the TiB2 phase toughening B4C ceramic is crack deflection and the pinning effect. Dislocations are observed

material.

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in the TEM image of the composite, which is beneficial to enhance the hardness and toughness of the

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Prime Novelty Statement

1) Analysis grain size distribution of B4C-TiB2 composites by electron backscattered diffraction (EBSD).

2) Dislocations are observed in the TEM image of the composite. 3) The toughening effect of TiB2 is explained comprehensively from crack deflection, grain size and microstructure defects (dislocations).

Author Statement Yingying Liu: Data curation, Writing- Original draft preparation Zhenqin Li: Software Yusi Peng: Software Yihua Huang: Formal analysis, Investigation, Conceptualization Zhengren Huang: Validation

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Deku Zhang: Project administration

Conflict Interest

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We declare that we have no financial and personal relationships with other people or

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organizations that can inappropriately influence our work.

Acknowledgment

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This project supported by the National Natural Science Foundation of China (Grant Nos

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51572276) and Youth Innovation Promotion Association, CAS.

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[28] D. Wang, S. Ran, L. Shen, H. Sun, Q. Huang, Fast synthesis of B4C–TiB2 composite powders by pulsed electric

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current heating TiC–B mixture, Journal of the European Ceramic Society, 35 (2015) 1107-1112. [29] X. Du, Z. Zhang, W. Wang, W. Hao, Z. Fu, Microstructure and properties of B4C-SiC composites prepared by polycarbosilane-coating/B4C powder route, Journal of the European Ceramic Society, 34 (2014) 1123-1129.

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[30] A. Li, Y. Zhen, Q. Yin, L. Ma, Y. Yin, Microstructure and properties of (SiC, TiB2)/B4C composites by reaction hot pressing, Ceramics International, 32 (2006) 849-856. [31] Won-Jin Moona, Toshiro Ito b, Shouji Uchimurab, Hiroyasu Saka c *, Toughening of ceramics by dislocation

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sub-boundaries, Materials Science and Engineering A, (2004) 837-839. [32] S.-M.C. Hideo Awaji *, Eisuke Yagi, Mechanisms of toughening and strengthening in ceramic-based. Mechanics of Materials, 34 (2002) 411-422. [33] F.J.S.m. Humphreys, Characterisation of fine-scale microstructures by electron backscatter diffraction (EBSD), Scripta material, 51 (2004) 771-776. [34] D. Fullwood, M. Vaudin, C. Daniels, T. Ruggles, S.I.J.M.C. Wright, Validation of kinematically simulated pattern HR-EBSD for measuring absolute strains and lattice tetragonality, Materials Characterization, 107 (2015) 270-277. [35] L. Germain, D. Kratsch, M. Salib, N.J.M.C. Gey, Identification of sub-grains and low angle boundaries beyond

the angular resolution of EBSD maps, Materials Characterization, 98 (2014) 66-72. [36] Skorokhod V, Krstic V D. High strength-high toughness B4C-TiB2 composites. Journal of materials science letters, 3 (2000) 237-239. [37] S. Yamada, K. Hirao, Y. Yamauchi, S.J.J.o.t.E.C.S. Kanzaki, High strength B4C–TiB2 composites fabricated by reaction hot-pressing, Journal of the European Ceramic Society, 23 (2003) 1123-1130. [38] Evans A G, Charles E A. Fracture toughness determinations by indentation. Journal of the American Ceramic

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Society, 59(1976) 371-372.

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Figure

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Fig.1. Particle size distribution of raw powders (a): B4C , (b): TiB2.

Fig.2.SEM images and XRD results of raw powders (a)-(b): B4C , (c)-(d): TiB2.

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Fig.3. SEM images of powders mixtures. (a) B05, (b)B10, (c)B20, (d)B30.

Fig.4 Relative density and hardness of the B20 sintered at different temperatures.

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Fig.5 Impact of TiB2 content on the relative density of samples.

Fig.6 Hardness and toughness of composites as a function of TiB2 content.

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Fig.7 XRD patterns of the B4C-TiB2 composites. (a) sample B20 sintered at different

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temperatures, (b) samples with different TiB2 content sintered at 1950℃.

Fig.8. SEM images of the surface of the B20 sintered at different temperatures. (a) 1800℃, (b) 1850℃, (c) 1900℃, (d) 1950℃.

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Fig.9. SEM images of the surface of composites with different TiB2 content sintered at

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1950℃: (a) B05, (b) B10, (c) B20, (d) B30; (e)-(g) EDS spectra of B20

Fig.10. SEM image of a fracture surface and crack propagation path of the B20.

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Fig.11. TEM images of the B20 and electron diffraction patterns.

Fig.12. EBSD phase image of B4C-TiB2 composites. (a) B05, (b) B10, (c) B20, (d) B30.

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Fig.13. The grain orientation of B4C-TiB2 composites. (a) B05, (b) B10, (c) B20, (d) B30.

Fig.14. The grain size distribution of the B4C phase in B4C-TiB2 composites.

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Fig.15. The grain size distribution of the TiB2 phase in B4C-TiB2 composites.

Fig.16. The average grain size of B4C and TiB2 in B4C-TiB2 composites as a function of TiB2 content.

Table Table 1 Characteristics of B4C and TiB2 powders Particle size (μm)

Purity (wt%)

Impurity level (wt%)

D90% of particles ‹ 1.01 D50% of particles ‹ 1.47

TiB2

98.90

Si:0.37

Fe:0.07

Cr:0.01

D10% of particle ‹ 2.10

Others:0.01

D90% of particles ‹ 0.424

Zr:11.28

Si:1.62

Y:0.24

Ca:0.09

D50% of particles ‹ 1.33

86.67

D10% of particle ‹ 3.72

Fe:0.06 Others:0.04

Table.2. Composition and nomenclature of the powder mixture Designation

B4C-5mol.%TiB2

B05

B4C-10mol.%TiB2

B10

B4C-20mol.%TiB2

B20

B4C-30mol.%TiB2

B30

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Composition.

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B4C

O:0.64

Sample no.

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Table.3. mechanical properties of samples sintered at different temperature Sintering temperature(℃) 1750

2

1800

3

1850

4 5

Hardness (GPa)

79.48

11.38 ± 0.35

83.82

16.25 ± 0.28

89.20

20.67 ± 0.31

1900

97.57

26.26 ± 0.31

1950

97.91

29.82 ± 0.14

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Relative density(%)

Table.4. mechanical properties of samples with different TiB2 content

Relative Density (%)

Hardness (GPa)

Fracture Toughness (MPa·m1/2)

B00

98.03

31.91±0.72

2.62 ± 0.1

B05

98.71

31.11±0.48

3.31 ± 0.04

B10

98.52

30.26±0.12

3.46 ± 0.07

B20

97.91

29.82±0.14

3.70 ± 0.08

B30

96.71

28.86±0.29

4.36 ± 0.1

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Sample code

Grain Diameter (μm) Sample code

D (TiB2)

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D (B4C) B00

1.91

B05

1.81

B10

1.71

1.23

B20

1.75

1.35

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B30

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Table.5. Grain diameter of sintered samples

1.45