Effects of Grain Grading on Microstructures and Mechanical Behaviors of Pressureless Solid‐State‐Sintered SiC

Abstract

S‐SiC ceramics with >96% of densification degree were derived from 0.8‐ to 8.6‐μm graded powders for the first time after sintered at 2210°C. Grain grading generated a 21.8% increase in green density and a 40.8% decrease in sintering shrinkage (low to 12.2%). The introduction of micrometer‐sized coarse particles suppressed abnormal grain growth owing to their pinning effect, thus resulting in equiaxial grains. Dramatically improved fracture toughness peaked to 3.77 MPa·m1/2 at 50 wt% of added coarse powder. Sintering mechanism of graded powders can be deduced as the bonding of coarse SiC particle through solid‐state sintering of fine powder.

Effects of initial α-phase content on the electrical, thermal, and mechanical properties of pressureless solid-state sintered SiC ceramics

“…According to Biswas's work [9] on the exural strength of hot-pressed SiC ceramics sintered with Al-B-C additives, the exural strength measured using the three-point bending method was approximately 150 MPa higher than that obtained using the four-point bending method. Thus, the exural strength values (289-335 MPa) of the present specimens measured by four-point bending are estimated to be superior to those (312-435 MPa, three-point bending) of PSS SiC ceramics with 0.5-1 wt% B 4 C and 3.1-4.7 wt% C [10,15,16]. Magnani et al [11,13] reported high exural strengths of 530-556 MPa for two-step sintered SiC ceramics with ne-grained microstructure compared to those (320-467 MPa) of PSS SiC ceramics with coarse-grained microstructures reported in other works [3,4,6,15,16].…”

“…Thus, the exural strength values (289-335 MPa) of the present specimens measured by four-point bending are estimated to be superior to those (312-435 MPa, three-point bending) of PSS SiC ceramics with 0.5-1 wt% B 4 C and 3.1-4.7 wt% C [10,15,16]. Magnani et al [11,13] reported high exural strengths of 530-556 MPa for two-step sintered SiC ceramics with ne-grained microstructure compared to those (320-467 MPa) of PSS SiC ceramics with coarse-grained microstructures reported in other works [3,4,6,15,16]. A ne-grained microstructure is bene cial in improving exural strength because of the reduced critical aw size [11,13].…”

“…A decreased critical aw size with increasing initial α-phase content indicates a superior sinterability of α-SiC compared to β-SiC powders, which is also indicated by a decreased scatter in exural strength values with the addition of α-SiC powders (refer to Table 4). 10,11,13,15,16]. A wide distribution of exural strength is due to the difference in composition, processing conditions and measurement methods among the various works.…”

“…According to Rudnayova et al's work[58] on the fracture toughness of hot pressed Si 3 N 4 ceramics measured using IF, ISB, and SENB methods, the fracture toughness varied by 3 MPa m 1/2 depending on the method and indentation load. Nonetheless, the literature[11,15] revealed that the low fracture toughness of PSS SiC ceramics is attributed to a strong interfacial bonding between the SiC grains, leading to a poor crack-microstructure interaction. Li et al's work[16] on PSS SiC ceramics with 0-5 wt% graphene suggests that the fracture toughness could be improved by adding graphene to promote crack de ection at SiC-graphene interfaces.…”

Si‐rich pressureless sintering of the gelcasted Ti3SiC2 bulk ceramic

“…In addition, a trimodal distribution is shown in Figure 1D, and the peaks were detected at 0.135, 2.164, and 17.191 μm, respectively. This means that a good gradation exists in the Ti 3 SiC 2 particles, which is beneficial to increase the solid loading content 41,42 …”