Low temperature sintering of Si₃N₄ceramics by spark plasma sintering technique

Abstract

Low temperature sintering of a-Si 3 N 4 matrix ceramics was developed in the present study using 4 wt-%MgO together with Al 2 O 3 or AlPO 4 as the sintering additives and spark plasma sintering technique. The results suggested that a-Si 3 N 4 ceramics could be densified at low sintering temperature by adjusting both the sintering temperature and sintering additive content. For low temperature sintered a-Si 3 N 4 ceramics, using MgO and Al 2 O 3 as the sintering additives, the densification is not complete at a temperature lower than 1600uC, and the mechanical strength is ,200 MPa. When MgO and AlPO 4 were used as the sintering additives, the increase in AlPO 4 content not only declines the sintering temperature but also promotes the mechanical property of the sintered Si 3 N 4 ceramics. It was the AlPO 4 phosphate binder that played a significant role in low temperature sintering of Si 3 N 4 ceramics.

Effect of ZrB2 content on phase assemblage and mechanical properties of Si3N4–ZrB2 ceramics prepared at low temperature

“…The toughness value of Si 3 N 4 -30 vol% ZrB 2 sample was higher or comparable with reported toughness values (6-10 MPa m 1/2 ) for Si 3 N 4 ceramics with obviously self-reinforced microstructure prepared at high temperature. [6][7][8] The strength values of Si 3 N 4 -30 vol% ZrB 2 sample were much higher than the reported strength values (300-500 MPa) for Si 3 N 4 ceramics prepared at low temperature, 12,13 but comparable or lower with the reported strength values (600-1000 MPa) for Si 3 N 4 ceramics with obviously self-reinforced microstructure prepared at high temperature. 6,[8][9][10] The high fracture toughness and fracture strength resulted from the reinforcing effects of the bimodal microstructures.…”

“…Si 3 N 4 ceramics prepared at low temperature contained major α‐Si 3 N 4 phase with high intrinsic hardness and demonstrated fine‐grained equiaxed microstructure, which led to high hardness (16‐20 GPa) . However, Si 3 N 4 ceramics prepared at low temperature showed low fracture toughness (3‐5 MPa m 1/2 ), and low flexural strength (300‐500 MPa) . It is worthy to manipulate the ratio of α‐ to β‐phase to better balance the mechanical properties (a combination of high hardness, strength, and toughness).…”

“…6 For comparison, the toughness values from the literature were obtained by a single-edge notched beam (SENB) method. Due to the reinforcing effect of bimodal microstructures, Si 3 N 4 ceramics showed high fracture toughness (6-10 MPa m 1/2 ) and high flexural strength (600-1000 MPa), whereas it possessed a relatively low Vickers hardness (13)(14)(15)(16) GPa). [6][7][8][9][10] Si 3 N 4 ceramics prepared at low temperature contained major a-Si 3 N 4 phase with high intrinsic hardness and demonstrated fine-grained equiaxed microstructure, which led to high hardness (16)(17)(18)(19)(20).…”

“…toughness (3-5 MPa m 1/2 ), 12 and low flexural strength (300-500 MPa). 12,13 It is worthy to manipulate the ratio of ato b-phase to better balance the mechanical properties (a combination of high hardness, strength, and toughness).…”

An Overview of Bearing Candidates for the Next Generation of Reusable Liquid Rocket Turbopumps

“…However, the machining property of Si 3 N 4 ceramic is poor due to its brittleness. The Si 3 N 4 rollers are usually fabricated by a sintering process with the necessary subsequent refining processes [30]. Their most common failure case falls into the breakdown mode.…”