Microstructure and mechanical properties of B₄C–TiB₂–SiC composites toughened by composite structural toughening phases

Abstract

B 4 C-TiB 2 -SiC composites toughened by composite structural toughening phases, which are the units of (TiB 2 -SiC) composite, were fabricated through reactive hot pressing with B 4 C, TiC, and Si as raw materials. The units of (TiB 2 -SiC) composite with the size of 10-20 lm are composed of interlocking TiB 2 and SiC with the size of 1-5 lm. The addition of TiC and Si can effectively promote the sintering of B 4 C ceramics. The relative densities of all the B 4 C composites with different contents of TiB 2 and SiC are close to completely dense (98.9%-99.4%), thereby resulting in superior hardness (33.1-36.2 GPa). With the increase in the content of TiB 2 and SiC, the already improved fracture toughness of the B 4 C composite continuously increases (5.3-6.5 MPaÁm 1/2 ), but the flexure strength initially increases and then decreases. When cracks cross the units of the (TiB 2 -SiC) composite, the cracks deflect along the interior boundary of TiB 2 and SiC inside the units. As the crack growth path is lengthened, the crack propagation direction is changed, thereby consuming more crack extension energy. The cumulative contributions improve the fracture toughness of the B 4 C composite. Therefore, the composite structural toughening units of the (TiB 2 -SiC) composite play an important role in reinforcing the fracture toughness of the composites. K E Y W O R D S boron carbide, ceramic matrix composites, hot pressing, mechanical properties, microstructure

Preparation of B4C composites toughened by MoB2/Mo2B5‐SiC interlocking structure via reactive hot pressing

“…Aside from the independent second-phase particles, the interlocking MoB 2 / Mo 2 B 5 and SiC with a particle size of approximately 10-25 μm are formed in the obtained composites. The interlocking structure is similar to the units of (TiB 2 -SiC) composite structural toughening phases fabricated in previous researches of Xiaorong Zhang et al [17][18][19] Hence, we successfully fabricate the B 4 C composites with MoB 2 /Mo 2 B 5 -SiC interlocking structure via reactive hot pressing with B 4 C and MoSi 2 as raw material. The amount of the second-phase particles (MoB 2 /Mo 2 B 5 and SiC) increases with the increasing MoSi 2 content.…”

“…Metal carbides such as Cr 2 C 3 11 and metaloxides 12,13 can also enhance the sinterability of B 4 C because they can react with B 4 C to form metal borides in situ. To change the single toughening structure, Xiaorong Zhang et al 17,18 successfully fabricated B 4 C-TiB 2 -SiC composites toughened by composite structural toughening phases, where the introduced second-phase particles (TiB 2 and SiC) are interlocked, rather than disperse independently in the matrix. This effect can notably improve the mechanical properties of B 4 C ceramics.…”

“…Despite the good results obtained by simply introducing one or two kinds of independent second-phase particles into B 4 C, the toughening effect is still limited due to the same independently dispersed toughening structure. To change the single toughening structure, Xiaorong Zhang et al 17,18 successfully fabricated B 4 C-TiB 2 -SiC composites toughened by composite structural toughening phases, where the introduced second-phase particles (TiB 2 and SiC) are interlocked, rather than disperse independently in the matrix. The method in their experiment is reactive hot pressing and the initial materials are B 4 C, TiC, and Si.…”

In situ toughened two‐phase B12(C, Si, B)3–SiC ceramics fabricated via liquid silicon infiltration

“…However, their naturally low fracture toughness and poor sinterability (sintering temperature >2000°C) limit their applications . Therefore, toughening phases, such as TiB 2 , ZrB 2 , and Al 2 O 3 are used to improve the fracture toughness of B 4 C ceramics, which generally ranges from 3 to 6.5 MPa·m 1/2 . Sintering additives, such as Al, B, C, Al 2 O 3 , or Al 2 O 3 –Y 2 O 3 , have been employed to decrease the sintering temperature and improve the SiC ceramic fracture toughness, which ranges from 2.5 to 8 MPa·m 1/2 .…”

Titanium diboride–silicon carbide–boron carbide ceramics with super‐high hardness and strength

“…Several examples of transition‐metal diboride‐silicon carbide‐boron carbide ceramics have been demonstrated. Grigoriev reported that additions of transition‐metal diborides and B 4 C improved the densification of SiC‐based compositions, with hardness values of ~26 GPa at a load of 5 N. Zhang et al demonstrated that reaction hot‐pressed B 4 C compositions reinforced with TiB 2 and SiC had hardness values up to ~36 GPa. Fahrenholtz et al reported a ZrB 2 –SiC–B 4 C ceramic with a hardness of ~43 GPa at 0.49 N.…”