Mechanical Properties Of Si3N4 Ceramics Research Articles

Fabrication of Si3N4 ceramics with adjustable microstructure and mechanical properties via Y2O3 contents in ZrN–AlN–Y2O3 ternary sintering additives

To adapt to the different application environments, Si3N4 ceramics are required to have different mechanical properties. Therefore, in this study, Si3N4 ceramics with adjustable mechanical properties were fabricated via using ZrN–AlN–Y2O3 ternary sintering additives and hot-pressing at 1650 °C for 30 min. Subsequently, the effect of the Y2O3 concentration on the phase assemblage, microstructure, mechanical properties, and crack propagation of Si3N4 ceramics was systematically investigated. The results demonstrated that Si3N4 ceramics presented adjustable microstructure and mechanical properties with the Y2O3 contents added in the range of 0∼8 wt%. With the increase of Y2O3 contents, the average aspect ratio of Si3N4 grains had an increase of 61.77%, increasing from 3.95 to 6.39. Besides, the Si3N4 grains and the formed YAG intergranular phase exhibited a fairly good combination at the nano-scale. Si3N4 grains and intergranular phase were the main influence factors on the mechanical properties of Si3N4 ceramics. As a result, the bending strength was from 700.99 ± 38.72 to 961.13 ± 36.84 MPa. The fracture toughness exhibited a range of 4.87 ± 0.11 to 6.10 ± 0.23 MPa⋅m1/2, while Vickers hardness achieved a high level of 16.09 ± 0.16 to 19.98 ± 0.39 GPa.

Effect of additive content on texture evolution and mechanical properties of Si3N4 ceramics prepared by hot pressing

The purpose of this research is to investigate influence of additive content on sintering behavior, texture evolution and mechanical properties of Si3N4 ceramics systematically. Si3N4 ceramics with different additive contents are prepared by hot pressing at 1750 °C for 1h. XRD analysis confirms that the densification process is dominated by particle rearrangement instead of phase transformation. Grain morphology characterization demonstrates that additive content affects relative amount between textured β-Si3N4 grains and β-Si3N4 nuclei during initial sintering. During subsequent sintering, β-Si3N4 nuclei surrounded by residual liquid phase elongated randomly, and then weaken texture degree of Si3N4 ceramics. The texture degree of Si3N4 ceramics decreases first and then increases as additives increase steadily. Based on the CTE misfit model and the stochastic model of crack propagation, texture degree, residual stress and grain size have a synergistic effect on crack propagation behavior of β-Si3N4 ceramics. The outstanding flexural strength (1096 MPa) and fracture toughness (10.61 MPa ∙ m1/2) is achieved in hot pressed SN21 with a relatively high texture degree (fL = 0.213).

Effect of Er2O3/MgO ratio on mechanical and thermal properties of Si3N4 ceramics

AbstractSi3N4 ceramics with high mechanical properties and thermal conductivity, exhibiting fine and bimodal microstructure, were prepared by adjusting the Er2O3/MgO ratio and hot‐pressing sintering at 1800°C for 4 h. The microstructure, grain distribution, lattice oxygen content, mechanical properties, and crack propagation process of the sintered bulk samples were systematically investigated. It was found that a low Er2O3/MgO ratio contributed to the densification of Si3N4 ceramics, whereas a high Er2O3/MgO ratio favored the grain growth of Si3N4 ceramics. In this research, the grain size distribution and average diameters as well as their impact on mechanical properties were examined. When the ratio of Er2O3/MgO was 3:1, Si3N4 had a larger average diameter and higher thermal conductivity, but the mechanical properties were somewhat reduced. When the ratio of Er2O3/MgO was 2:2, the sample displayed enhanced mechanical performance, which can be explained by the formation of a bimodal structure. The research indicates that it is feasible to control the microstructure and optimize the mechanical properties of Si3N4 ceramics by tailoring the sintering additives.

Realizing mechanical property improvement and coloration in Si3N4 ceramics by rare earth-doping

Si3N4 ceramics, due to their exceptional comprehensive performance, have potential applications in electronic products under the 5th generation mobile communication technology. However, their development is hindered by a lack of color variety and inherent brittleness. To address these issues, we propose the use of an appropriate colorant-sintering additive to enhance densification, promote the growth of β grains and facilitate the formation of a chromogenic phase. This approach aims to simultaneously adjust the color and mechanical properties of Si3N4 ceramics. STEM-EDS results indicate the presence of Re-enriched hollow structures within the Si3N4 matrix. These hollow structures may serve as one of the color centers of silicon nitride. The combined effects of the stress field surrounding the hollow structure, elongated β-Si3N4 grains and intensive dislocations result in strong mechanical properties of Si3N4 ceramics, in which the flexural strength is 852.7 ± 55.8 MPa and the fracture toughness is 11.7 ± 1.0 MPa m1/2.

Effect of sintering aids content and powder characteristics on gas pressure sintered Si3N4 ceramics

The Si3N4 raw powder, sintering aids, and sintering process are the most critical factors affecting the thermal conductivity and mechanical properties of Si3N4 ceramics. The impact of sintering aids content and powder characteristics on gas pressure sintered Si3N4 ceramics was investigated in this study. Lower aids content facilitated phase transformation prior to densification, promoting a pronounced bimodal microstructure. Based on in-situ shrinkage behavior, liquid phase sintering of Si3N4 ceramics can be divided into three stages without clear boundaries. Between 1200 and 1400 °C, higher oxygen and metallic impurities favored particle rearrangement. Between 1400 and 1800 °C, the dissolution and precipitation process was probably controlled by the α-phase ratio and particle size. Above 1800 °C, subsequent grain growth was primarily facilitated by the Ostwald ripening process, leading to a reduced densification rate. Higher oxygen content leading to greater weight loss during sintering. Higher Fe resulted in a darker color of sintered Si3N4 ceramics. High α-phase content promoted the formation of a bimodal microstructure and ensured superior mechanical properties. Reduced levels of oxygen and aluminum were prerequisites for achieving high thermal conductivity. Powders prepared by silicon nitriding method were cost-effective materials for the preparation of high-performance Si3N4 ceramic substrates.

Mechanical and thermal properties of Si3N4 ceramics prepared by gelcasting using high-solid-loading slurries

In this study, according to the Dinger model, aqueous Si3N4 slurries with a solid loading of 63 vol% and a viscosity lower than 1.0 Pa s were successfully prepared using two-grade Si3N4 powders with D50 = 7.2 μm and 9.4 μm as starting materials. These resulting slurries exhibited good rheological properties and suspension stability. Notably, the presence of β-Si3N4 seeds existed in the starting materials effectively reduced the nucleation barrier by transforming homogeneous nucleation into heterogeneous nucleation. Consequently, it facilitated the reconstructive phase transformation of α-Si3N4 to β-Si3N4, promoted the anisotropic growth of β-Si3N4 nucleation, and resulted in the final formation of the bimodal microstructure. This unique microstructure significantly enhanced the mechanical properties of Si3N4 ceramics, resulting in a high flexural strength of 1011.4 MPa and a fracture toughness of 14.8 MPa m1/2. These excellent properties were achieved through the combination of gelcasting and gas pressure sintering. Simultaneously, the Si3N4 ceramics exhibited a low thermal conductivity of 47.7 W m−1 K−1, mainly owing to the low density of 95.3 %, the presence of low-thermal-conductivity silicate-based noncrystalline substances, and the possible existence of lattice oxygen in Si3N4 crystals.

Effects of MgO-RE2O3 and SiO2-RE2O3 (RE = La, Nd, Gd, Ho and Lu) complex sintering additives on the phase composition, microstructure and mechanical properties of dual-phase Si3N4 ceramics

Dual-phase (α+β)-Si3N4 ceramics with MgO-RE2O3 and SiO2-RE2O3 (RE = La, Nd, Gd, Ho and Lu) complex sintering additives were prepared by SPS at 1650 and 1700 °C. The effect of sintering additives on the phase transition, microstructure evolution and mechanical properties of the Si3N4 ceramics were studied. For the MgO-RE2O3 samples, as the RE radius increased, the phase transition was decelerated, the percentage of rod-like grains and fracture toughness decreased and the hardness showed a hill-shape curve. It is proposed that the effect of RE radius is connected with the segregation behavior of RE cations on the surface of Si3N4 grains. For the SiO2-RE2O3 samples, as the RE radius increased, the phase transition was accelerated and the percentage of rod-like grains increased. It is suggested that the effect of RE radius is related with the liquid phase viscosity and nitrogen solubility.

Effect of the ratio of Y2O3 and MgSiN2 sintering additives on the microstructure, thermal and mechanical properties of Si3N4 ceramics

To investigate the mechanism of the influence of the sintering additive ratio on the microstructure evolution of silicon nitride (Si3N4) ceramics, Si3N4 ceramics were prepared by gas pressure sintering using different ratios of Y2O3/MgSiN2 as additives. Varying the ratio of Y2O3/MgSiN2 changed the composition of the liquid phase, thereby affecting the densification process and phase transformation rate of Si3N4 ceramics, and ultimately changing their microstructure. The reduction in the Y2O3/MgSiN2 ratio raised the N/O and Si/O ratios in the system, which increased the liquid phase viscosity. The Si3N4 grain distribution varied from "normal to bimodal". In the case of increasing the proportion of MgSiN2 and prolonging the sintering time, more of the glass phase evaporated, which reduced the content of the low thermal conductivity phase and increased the continuity of Si3N4/Si3N4. Therefore, Si3N4 ceramics with 1 wt% Y2O3 and 5 wt% MgSiN2 exhibited excellent properties after sintering at 1900 °C for 12 h, with thermal conductivity, bending strength, and fracture toughness of 106.7 Wm−1K−1, 776 MPa, and 11.66 MPa m1/2, respectively.

Additive manufacturing of complex-shaped and porous silicon nitride-based components for bionic bones

Si3N4 is a novel implant material with promising applications in the replacement of human hard tissues. The biomimetic human bone structure used in this study was created using digital light-processing technology. The effect of pore-forming agent content on the curing and mechanical properties of Si3N4 ceramics was studied. The obtained results indicated that with an increase in the pore-forming agent content, the cure depth of the ceramic suspension first increased and then decreased, while the excess cure width decreased. Furthermore, as the pore-forming agent content increased, the porosity of the sample increased, whereas the compressive strength and Young's modulus decreased. The maximum porosity of the sample at the optimal mass ratio (pore-forming agent: Si3N4 = 5:10) is 58.48 ± 0.49%, and the compressive strength and Young's modulus are 79.01 ± 6.78 MPa and 18.18 ± 0.26 GPa, respectively.

Cure behaviour and mechanical properties of Si3N4 ceramics with bimodal particle size distribution prepared using digital light processing

Digital light processing is a vital additive manufacturing technology used for manufacturing ceramic parts. The particle size distribution of ceramic suspensions significantly affects the cure behaviour and mechanical properties of ceramics. In this study, the cure behaviour and mechanical properties of Si3N4 ceramics with a bimodal particle size distribution were studied. The results indicated that the suspension with coarse particles had a higher cure depth for a lower absorbance but poor mechanical properties. The bending strength of the samples with the optimal ratio (coarse:fine particles = 3:7) reached a maximum of 728.7 ± 10.33 MPa, which is 16.5% higher than that of the samples prepared using only fine particles.

Thermal and mechanical properties of Si3N4 ceramics obtained via two-step sintering

Si3N4 ceramics were prepared using novel two-step sintering method by mixing α-Si3N4 as raw material with nanoscale Y2O3–MgO via Y(NO3)3 and Mg(NO3)2 solutions. Si3N4 composite powders with in situ uniformly distributed Y2O3–MgO were obtained through solid–liquid (SL) mixing route. Two-step sintering method consisted of pre-deoxidization at low temperature via volatilization of in situ-formed MgSiO3 and densification at high temperature. Variations in O, Y, and Mg contents in Si3N4–Y2O3–MgO during first sintering step are discussed. O and Mg contents decreased with increasing temperature because SiO2 on Si3N4 surface reacted with MgO to form low-melting-point MgSiO3 compound, which is prone to volatilize at high temperature. By contrast, Y content hardly changed due to high-temperature stability of Y–Si–O–N quaternary compound. In the second sintering step, skeleton body was densified, and the formation of Y2Si3O3N4 secondary phase occurred simultaneously. Two-step sintered Si3N4 ceramics had lower total oxygen content (1.85 wt%) than one-step sintered Si3N4 ceramics (2.51 wt%). Therefore, flexural strength (812 MPa), thermal conductivity (92.1 W/m·K), and fracture toughness (7.6 MPa⋅m1/2) of Si3N4 ceramics prepared via two-step sintering increased by 28.7%, 16.9%, and 31.6%, respectively, compared with those of one-step sintered Si3N4 ceramics.

Investigation on thermal conductivity and mechanical properties of Si3N4 ceramics via one-step sintering

High thermal conductivity Si3N4 ceramics were fabricated using a one-step method consisting of reaction-bonded Si3N4 (RBSN) and post-sintering. The influence of Si content on nitridation rate, β/(α+β) phase rate, thermal conductivity and mechanical properties was investigated in this work. It is of special interest to note that the thermal conductivity showed a tendency to increase first and then decrease with increasing Si content. This experimental result shows that the optimal thermal conductivity and fracture toughness were obtained to be 66 W (m K)-1 and 12.0 MPa m1/2, respectively. As a comparison, the nitridation rate and β/(α+β) phase rate in a static pressure nitriding system, i.e., 97% (MS10), 97% (MS15), 97% (MS20) and 8.3% (MS10), 8.3% (MS15), 8.9% (MS20), respectively, have obvious advantages over those in a flowing nitriding system, i.e., 91% (MS10), 91% (MS15), 93% (MS20) and 3.1% (MS10), 3.3% (MS15), 3.3% (MS20), respectively. Moreover, high lattice integrity of the β-Si3N4 phase was observed, which can effectively confine O atoms into the β-Si3N4 lattice using MgO as a sintering additive. This result indicates that one-step sintering can provide a new route to prepare Si3N4 ceramics with a good combination of thermal conductivity and mechanical properties.

Thermal conductivity and mechanical properties of Si3N4 ceramics with binary fluoride sintering additives

Silicon nitride (Si3N4) ceramics were fabricated by gas pressure sintering (GPS) using four sintering additives: Y2O3–MgO, Y2O3–MgF2, YF3–MgO, and YF3–MgF2. The phase composition, grain growth kinetics, mechanical properties, and thermal conductivities of the Si3N4 ceramics were compared. The results indicated that the reduction of YF3 on SiO2, induced a high Y2O3/SiO2 secondary phase ratio, which improved the thermal conductivity of the Si3N4 ceramics. The depolymerization of F atom reduces the diffusion energy barrier of solute atom and weakens the viscous resistance of anion group, which was beneficial to grain boundary migration. Besides exhibiting a lower grain growth exponent(n = 2.5)and growth activation energy (Q = 587.94 ± 15.35 kJ/mol), samples doped with binary fluorides showed excellent properties, including appreciable thermal conductivity (69 W m−1 K−1), hardness (14.63 ± 0.12 GPa), and fracture toughness (8.75 ± 0.18 MPa m1/2), as well as desirable bending strength (751 ± 14 MPa).

Effect of ZrB2 and its oxide impurities (ZrO2 and B2O3) on hot-pressed Si3N4 ceramics at low temperature

Based on the previous work on Si3N4-ZrB2, the addition of 2.5 vol.% ZrB2 promoted α- to β-Si3N4 phase transformation, bimodal microstructure, and toughness and strength improvement after hot-pressing at 1500 °C. However, the mechanism needed to be further explored. In the present work, the effect of ZrB2 and its oxide impurities (ZrO2 and B2O3) on phase composition, microstructure and mechanical properties of Si3N4 ceramics with MgO-Yb2O3 additives were studied. Results showed that the addition of B2O3 had no influence on Si3N4 ceramics, whereas the addition of ZrO2 inhibited the α- to β-Si3N4 phase transformation, formed an uniform equiaxed microstructure, and deceased the toughness and strength. The positive effect of oxide impurities can be eliminated. Based on the STEM analysis, the possible reason was that the addition of ZrB2 led to the formation of Si-Mg-O-N-Yb-Zr-B liquid phase, and then promoted α- to β-Si3N4 phase transformation.

Influence of hexagonal boron nitride nanosheets on phase transformation, microstructure evolution and mechanical properties of Si3N4 ceramics

Fully dense Si3N4 materials with 1 wt.% (∼ 1.5 vol.%) and 2 wt.% (∼ 3.0 vol.%) h-BN nanosheets were prepared by spark plasma sintering at 1750 °C with the dwell of 7 min under a pressure of 50 MPa in a vacuum. BN nanosheets with different dimensions were prepared by ultrasound-assisted liquid phase exfoliation of h-BN powder, followed by centrifugation at different speeds (1000 rpm and 3000 rpm). The addition of BN nanosheets hindered the particle rearrangement stage of sintering, which resulted in the delayed α→β phase transformation of Si3N4. To study a direct effect of BN nanosheets on the mechanical properties of Si3N4, the results were compared to the monolithic Si3N4 with similar grain size and α/β-Si3N4 ratio. The addition of 2 wt.% h-BN nanosheets (1000 rpm) increased both the fracture toughness (∼ 26 %) and the strength (∼ 45 %) of Si3N4, when compared to the monolithic Si3N4 with similar microstructure.

Enhanced mechanical properties of Si3N4 ceramics with ZrB2-B binary additives prepared at low temperature

Phase composition, microstructures, and mechanical properties of silicon nitride (Si3N4) ceramics were investigated with ZrB2 and B additives. Results showed that the addition of ZrB2 and/or B in 2.5 and 5 vol.% promoted the phase transformation of α- to β-Si3N4 phase and the formation of bimodal microstructure after hot-pressing at 1500 °C. With the introduction of 2.5 vol.% (ZrB2-B) binary additives, fracture toughness and strength of Si3N4 ceramics increased significantly from 5.2 MPa m1/2 and 384 MPa to 7.2 MPa m1/2 and 675 MPa, respectively. However, the hardness of ceramics decreased slightly from 23.5 GPa to 21.3 GPa, which was still higher than typical values reported on Si3N4 ceramics (15˜17 GPa).

Effect of powder characteristics on the thermal conductivity and mechanical properties of Si3N4 ceramics sintered by Spark plasma sintering

The effect of powder characteristics on the thermal conductivity and mechanical properties of silicon nitride (Si 3 N 4 ) ceramics were investigated systematically by using two α-Si 3 N 4 powders a ...

Effect of nano-sized sintering additives on microstructure and mechanical properties of Si3N4 ceramics

Nano-sized sintering additives such as MgO, Al2O3, Y2O3 and La2O3 are added to process Si3N4 based ceramics. The effects of such sintering additives on the phase transformation, mechanical properties and microstructure of silicon nitride were investigated. XRD analysis of sintered silicon nitride with these sintering additives have shown the complete transformation of α-Si3N4 into β-Si3N4. The silicon nitride ceramics sintered with nano-sized additives (4MgO-4Al2O3–5La2O3) have exhibited the highest fracture toughness. This is not only due to the weak glass|grain interface but also due to the formation of high aspect ratio grains (β-Si3N4). Superior mechanical properties of Si3N4 can be obtained by way of adding small and large RE3+ radii RE2O3 (Y2O3 and La2O3) together than the addition of single RE2O3.

The effect of T-ZnOw addition on the microstructure, mechanical and antibacterial properties of Si3N4 ceramics for biomedical applications

Si3N4 ceramics with constant proportion of sintering aids and different mass percentages of tetra-needle-like ZnO whisker (T-ZnOw) added were prepared by gas pressure sintering process at 1700 °C under an applied pressure of 4 MPa for 2 h. The microstructure, mechanical and antibacterial properties of Si3N4 ceramics were characterized and investigated. The results indicated that T-ZnOw could be well- dispersed in the sintered ceramic matrix and grain size of Si3N4 ceramics became larger with the addition of T-ZnOw. Moreover, the mechanical properties of Si3N4 ceramics with T-ZnOw added were slightly lower than those of samples without T-ZnOw added for the unnoticeable negative effects of T-ZnOw. Additionally, Si3N4 ceramics with T-ZnOw added possessed superior antibacterial rate against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) compared with samples without T-ZnOw added owing to generation and release of reactive oxygen and Zn2+ ions that could inhibit the growth of bacteria.

Comparative study of fluoride and non-fluoride additives in high thermal conductive silicon nitride ceramics fabricated by spark plasma sintering and post-sintering heat treatment

High thermal conductivity silicon nitride (Si3N4) ceramics fabricated using fluoride and non-fluoride additives were comparatively investigated in this study for the first time. Three series of sintering aids, namely, MgF2-Y2O3, MgSiN2-Y2O3 and MgO-Y2O3 were used to fabricate Si3N4 ceramics by spark plasma sintering (SPS) at 1650 ℃ for 5 min and post-sintering heat treatment at 1900 ℃ for 4 h. Microstructure, thermal conductivity, and mechanical properties of Si3N4 ceramics were comparative investigated. Results indicate that MgF2 as sintering additive for Si3N4 ceramics is able to effectively reduce the temperature of liquid phase in SPS process. The proportion of large grains is about 34% in fluoride-doped sample, which is more than those samples using MgSiN2 and MgO as sintering aids (24% and 25%, respectively). Thermal conductivity of ceramics is 76, 64, and 60 Wm−1 K−1 for samples with MgF2, MgSiN2 and MgO, respectively. Fluoride-doped sample displayed good mechanical properties including bending strength (857.6 MPa), hardness (14.9 GPa), and fracture toughness (7.7 MPa m1/2).