Influence of ZrH2 addition on pulsed electric current sintered ZrB2–SiC composites (original) (raw)
Related papers
Journal of the Ceramic Society of Japan, 2010
Dense ZrB 2 SiC and HfB 2 SiC composites were fabricated at 1800°C by spark plasma sintering (SPS) using TaSi 2 as sintering aid. The volume content of SiC was 530% and that of TaSi 2 was 5% in the initial compositions. The additive of TaSi 2 contributed to the densification of composites by the decomposition and simultaneous solid solution of Ta atoms into boride grains which was probably associated with the decrease of activation energy of boride grain boundaries. With increasing SiC content, the electrical conductivity of ZrB 2 SiC and HfB 2 SiC composites decreased from 19.89 to 11.99 and 22.29 to 13.42 © 10 5 ³ ¹1 •m ¹1 respectively. Generally, the thermal conductivity of composites showed an increasing tendency with increasing SiC content, indicating the maximum values of 49.93 and 118.39 W/m•K respectively for ZrB 2 SiC and HfB 2 SiC composites produced with 30 vol % SiC content in the initial compositions. Additionally, the Vickers hardness of composites increased with the increment of SiC content from 16.9 to 20.2 and 24.0 to 28.5 GPa for ZrB 2 SiC and HfB 2 SiC composites respectively. The fracture toughness of ZrB 2 SiC composites showed an increasing tendency from 3.70 to 4.44 MPa•m 1/2 with increasing SiC content while those of HfB 2 SiC composites did not show a changing tendency and was in a range of 3.28 3.54 MPa•m 1/2. The elastic moduli of composites declined from 464.8 to 453.2 and 494.4 to 481.9 GPa for ZrB 2 SiC and HfB 2 SiC composites respectively with increasing SiC content.
Synergistic influence of SiC and C3N4 reinforcements on the characteristics of ZrB2-based composites
Journal of Asian Ceramic Societies
In this work, ZrB 2-SiC and novel C 3 N 4-doped ZrB 2-SiC composites were manufactured at 1850° C under an external load of 40 MPa for 6 min via spark plasma sintering. The effects of C 3 N 4 on the mechanical characteristics (flexural strength, Vickers hardness, and fracture toughness) and microstructure of the ZrB 2-SiC-based composites were investigated. By adding 5 wt% g-C 3 N 4 , a fully dense ceramic composite was fabricated, compared to the C 3 N 4-free ZrB 2-SiC composite with a relative density of 95%. Removal of ZrO 2 and B 2 O 3 from the surface of ZrB 2 particles via chemical reactions with C 3 N 4 , and the in-situ synthesis of ZrC and BN as new phases were studied by XRD and SEM analyses. Indentation fracture toughness, flexural strength, and Vickers hardness improved from 4.5 MPa.m 1/2 , 460.2 MPa and 17.4 GPa to 6.1 MPa.m 1/2 , 580.2 MPa and 21.2 GPa, respectively, by adding g-C 3 N 4 to the ZrB 2-SiC ceramic.
Journal of the European Ceramic Society, 2010
ZrB 2-SiC composites were fabricated by spark plasma sintering (SPS) using TaSi 2 as sintering additive. The volume content of SiC was in a range of 10-30% and that of TaSi 2 was 10-20% in the initial compositions. The composites could be densified at 1600 • C and the core-shell structure with the core being ZrB 2 and the shell containing both Ta and Zr as (Zr,Ta)B 2 appeared in the samples. When the sintering temperature was increased up to 1800 • C, only (Zr,Ta)B 2 and SiC phases could be detected in the samples and the core-shell structure disappeared. Generally, the composites with core-shell structure and fine-grained microstructure showed the higher electrical conductivity and Vickers hardness. The completely solid soluted composites with coarse-grained microstructure had the higher thermal conductivity and Young's modulus.
Journal of the Ceramic Society of Japan, 2018
ZrB 2 SiC composite ceramics were fabricated by spark plasma sintering SiC powders with various mixtures of ZrB 2 , Zr, Al and graphite components, toughening the ceramics through the in-situ synthesis of ZrAlC microstructures. Different microstructures of ZrAlC toughened ZrB 2 SiC (ZSA) composite ceramics were formed during the sintering process by varying the components ball milled with the ZrB 2 powders prior to sintering. When the milled ZrB 2-based powders contained Al, the major ZrAlC phase changed into Zr 3 Al 4 C 6 from the designed Zr 2 Al 4 C 5 , and the layered ZrAlC grains formed with a large aspect ratio in the ZSA ceramics due to the formation of an Al-based coating layer covering the ZrB 2 powders during milling process. The Zr and Al co-milled ZrB 2-based powders further improved the toughness of composite ceramics through a more uniform distribution and the larger aspect ratio of ZrAlC grains. As a result, the ZSA ceramic made using the milled powders of ZrB 2 , Zr and Al showed the highest fracture toughness of 5.96 MPa•m 1/2 , about 10% higher than that of the ceramic made using milled ZrB 2 and Zr powders. The toughening mechanisms are shown to be crack deflection and bridging caused by ZrAlC grains. This work points to a possible pathway to control the microstructure of ZrAlC grains for toughening ZrB 2 SiC composite ceramics.
Scripta Materialia, 2007
Four kinds of composites, ZrB 2 -SiC, ZrB 2 -SiC-ZrC, ZrB 2 -SiC-ZrN and ZrB 2 -SiC-AlN, were synthesized in situ via reactive hot pressing (RHP) and reactive spark plasma sintering (R-SPS), using Zr, Si, B 4 C, BN and Al as raw materials. The synthesis process plays a critical role in the microstructural features of the composites obtained. The R-SPS process can lead to a more homogeneous and finer microstructure due to its high heating rates and short holding time, while the RHP process is likely to result in coarse microstructures due to a long enough holding time for grains growth.
Mechanical and oxidation behavior of spark plasma sintered ZrB2–ZrC–SiC composites
Journal of the Ceramic Society of Japan, 2012
ZrB 2 ZrCSiC composites were prepared by spark plasma sintering (SPS) at temperatures of 1750°C for 300 s under a pressure of 40 MPa. Densification, microstructural, mechanical properties and oxidation behavior of the composites were investigated. Fully dense ZrB 2 ZrCSiC composites with a relative density of more than 99% were obtained at 1750°C for 300 s. Vickers hardness of ZrB 2 ZrCSiC composites decreased with increasing ZrC content from 20 to 40 vol %, and composite containing 60 vol % ZrB 2 , 20 vol % ZrC and SiC sintered at 1750°C for 300 s had the highest value of 21.1 GPa. The crack mode for the same composite was zigzag, and resulted in remarkable crack deflections and the highest fracture toughness value of 5.5 MPa•m 1/2. Oxidation of composites resulted in formation of protective layered oxide structures consisted of ZrO 2 and SiO rich layer in the form of SiO 2 or SiO, and normalized mass change results increased with increasing oxidation temperature.
2010
Starting from a ZrB 2 matrix, composites containing 10, 20 vol% of SiC whiskers and 20 vol% of SiC-chopped fibers were sintered by spark plasma sintering at 15001C. The addition of whiskers allowed both strengthening (740-770 MPa) and toughening (5.1-5.7 MPa . m 1/2 ) compared with the reference material. In the fiber-reinforced composite, the increase in fracture toughness (5.5 MPa . m 1/2 ) was accompanied by a decrease of strength (370 MPa). Toughening mechanisms were explored through the analysis of crack propagation. Crack deflection, crack pinning, and thermal residual stresses were the most important mechanisms identified. The experimental toughness increase was successfully compared with the values predicted by theoretical models. Compared with the baseline material, the reinforced composites showed an increased strength at 12001C in air. The highest value, 450 MPa, was for the fiber-reinforced composite.
In the present paper, ZrB 2-HfB 2 composite was produced by pressureless sintering method and SiC, MoSi 2 and B 4 C particles were used as additive. In order to produce composite samples, ZrB 2 powder was first milled for 2 hours and then the reinforcing particles were added to milled powder. The mixture was formed by cold isostatic press (CIP) and after pyrolysis, was sintered at 2100⁰C. In order to compare the effect of different additives on pressureless sintering behavior of ZrB 2-HfB 2 composite, the shrinkage percentage of samples were measured before and after sintering and the microstructure of samples were examined using Scanning Electron microscopy (SEM), equipped with EDS spectroscopy. Bending test was used to measure the strength and the elastic modulus of samples was measured by resonance frequency method. The results show that samples containing MoSi 2 and SiC nano-particles have the maximum flexural strength and elastic modulus. The reason is the better effect of MoSi 2 particles on sintering process and densification comparing to B 4 C particles.
Ceramics International, 2018
ZrB 2-based ceramics, reinforced with 25 vol% SiC whiskers (SiC w) as well as 0, 2.5, 5 and 7.5 wt% carbon nanoparticles (C np), were prepared by spark plasma sintering (SPS) at 1900 ºC under 40 MPa for 7 min in a vacuum environment. The influences of C np content on densification behavior, microstructure evolution, hardness and fracture toughness of ZrB 2-SiC w ceramics were investigated. Compared to the carbon-free sample, the grain growth of ZrB 2 matrix was moderately decreased (~20%) after the addition of C np. The in-situ formation of B 4 C and ZrC phases was attributed to the elimination of surface oxide impurities through their chemical reactions with the C np additive. All composite samples approached their theoretical densities. A hardness of 21.9 GPa was obtained for ZrB 2-SiC w sample, but the hardness values linearly decreased by the addition of soft carbon additives and reached 14.6 GPa for the composite doped with 7.5 wt% C np. The fracture toughness showed another trend and increased from 4.7 MPa m ½ for the carbon-free sample to 7.1 MPa m ½ for 5 wt% C np-reinforced composite. The formation of new carbides and the presence of unreacted C np resulted in toughness improvement. Various toughening mechanisms such as crack branching, bridging, and deflection were detected and discussed.
Applied Physics A, 2005
A fully dense ZrB 2 ceramic containing 10 vol. % ultra-fine α-SiC particulate was successfully hot pressed at 1900 • C for 20 min and 40-50 MPa of applied pressure. Faceted ZrB 2 grains (average size ≈ 3 µm) and SiC particles dispersed regularly characterized the base material. No extra secondary phases were found. The introduction of the ultra-fine α-SiC particulate was recognized as the key factor that enabled both the control of the diboride grain growth and the achievement of full density. The mechanical properties offered an interesting combination of data: 4.8 ± 0.2 MPa √ m fracture toughness, 507 ± 4 GPa Young's modulus, 0.12 Poisson's ratio, and 835 ± 35 MPa flexural strength at room temperature. The flexural strength measured at 1500 • C (in air) provided values of 300 ± 35 MPa. The incorporated ultra-fine α-SiC particulate was fundamental, sinterability apart, to enhancing the strength and oxidation resistance of ZrB 2. The latter property was tested at 1450 • C for 20 h in flowing dry air. In such oxidizing conditions, the formation of a thin external borosilicate glassy coating supplied partial protection for the faces of the material exposed to the hot environment. The oxidation attack penetrated into the material's bulk and created a 200-µm-thick zirconia scale. The SiC particulate included in the oxide scale, lost by active oxidation, left carbon-based inclusions in the formerly occupied sites.