Advantages and disadvantages of graphite addition on the characteristics of hot-pressed ZrB2–SiC composites (original) (raw)
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Ceramics International, 2015
Hot pressed monolithic ZrB 2 ceramic (Z), ZrB 2-20 vol% SiC composite (ZS 20) and ZrB 2-20 vol% SiC-10 vol% nano-graphite composite (ZS 20 G n10) were investigated to determine the influence of graphite nano-flakes on the sintering process, microstructure, and mechanical properties (Vickers hardness and fracture toughness) of ZrB 2-SiC composites. Hot pressing at 1850 1C for 60 min under 20 MPa resulted in a fully dense ZS 20 G n10 composite (relative density: 99.6%). The results disclosed that the grain growth of ZrB 2 matrix was efficiently hindered by SiC particles as well as graphite nano-flakes. The fracture toughness of ZS 20 G n10 composite (7.1 MPa m 1/2) was essentially improved by incorporating the reinforcements into the ZrB 2 matrix, which was greater than that of Z ceramic (1.8 MPa m 1/2) and ZS 20 composite (3.8 MPa m 1/2). The fractographical observations revealed that some graphite nano-flakes were kept in the ZS 20 G n10 microstructure, besides SiC grains, which led to toughening of the composite through graphite nano-flakes pull out. Other toughening mechanisms such as crack deflection and branching as well as crack bridging, due to the thermal residual stresses in the interfaces, were also observed in the polished surface.
Synthesis and Sintering
The incorporation of 1 wt% hexagonal BN (hBN) into ZrB2–30 vol% SiC could noticeably better the fracture toughness, hardness, and consolidation behavior of this composite. This research intended to scrutinize the effects of various amounts of hBN (0–5 wt%) on different characteristics of ZrB2–SiC materials. The hot-pressing method under 10 MPa at 1900 °C for 120 min was employed to sinter all designed specimens. Afterward, the as-sintered samples were characterized using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and Vickers technique. The hBN addition up to 1 wt% improved relative density, leading to a near fully dense sample; however, the incorporation of 5 wt% of such an additive led to a composite containing more than 5% remaining porosity. The highest Vickers hardness of 23.8 GPa and fracture toughness of 5.7 MPa.m1/2 were secured for the sample introduced by only 1 wt% hBN. Ultimately, breaking l...
Effects of nano-graphite content on the characteristics of spark plasma sintered ZrB2–SiC composites
Materials Science and Engineering: A, 2018
In this study, ZrB 2-25 vol% SiC composite containing 0, 2.5, 5, 7.5 and 10 wt% graphite nanoflakes were prepared by spark plasma sintering (SPS) process at 1900 ºC for 7 min under 40 MPa. The fabricated composite samples were compared to examine the influences of nanographite content on the densification, microstructure and mechanical properties of ZrB 2-SiCbased ultrahigh temperature ceramics. Fully dense composites were obtained by adding 0-5 wt% nano-graphite, but higher amounts of additive led to a small drop in the sintered density. The growth of ZrB 2 grains was moderately hindered by adding nano-graphite but independent of its content. The hardness linearly decreased from 19.5 for the graphite-free ceramic to 12.1 GPa for the sample doped with 10 wt% nano-graphite. Addition of graphite nano-flakes increased the fracture toughness of composites as a value of 8.2 MPa m ½ was achieved by adding 7.5 wt% nano-graphite, twice higher than that measured for the graphite-free sample (4.3 MPa m ½). The in-situ formation of ZrC and B 4 C nano-particles as well as the presence of unreacted graphite nano-flakes led to a remarkable enhancement in fracture toughness through activating several toughening mechanisms such as crack deflection, crack bridging, crack branching and graphite pullout.
Influence of SiAlON addition on the microstructure development of hot-pressed ZrB2–SiC composites
Ceramics International, 2020
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Characterization of hot-pressed graphene reinforced ZrB 2 –SiC composite
Materials Science and Engineering: A, 2015
In this paper, the hot pressing of monolithic ZrB 2 ceramic (Z), ZrB 2-25 vol% SiC composite (ZS), as well as 5 wt% graphene reinforced ZrB 2-25 vol% SiC composite (ZSG) is investigated. The hot pressing at 1850 1C for 60 min under a uniaxial pressure of 20 MPa resulted in a near fully-dense ZSG composite (499% relative density). In addition, the influence of graphene reinforcement on the sintering process, microstructure, and mechanical properties (Vickers hardness and fracture toughness) of ZrB 2-SiC composite is discussed. It was disclosed that the grain growth of the ZrB 2 matrix was effectively stopped by SiC particles and graphene nano-platelets. The fracture toughness of ZSG composite (6.4 MPa m 1/2) was strongly enhanced by incorporating the mentioned reinforcements into the ZrB 2 matrix, which is higher than that of Z ceramic (1.8 MPa m 1/2) and ZS composite (4.3 MPa m 1/2). After the hot pressing process, the fractographical outcomes revealed that some graphene nano-platelets were kept in the composite microstructure, apart from SiC grains, which lead to the toughening of the composite through graphene nano-platelets wrapping and pull out, crack deflection, and crack bridging.
International Journal of Refractory Metals and Hard Materials, 2015
In this paper, the effects of the hot pressing parameters and SiC content on the densification of ZrB 2-based composites have been studied. This research reports a design of experiment approach, the Taguchi method, employed to analyze the processing of ZrB 2-SiC composites based on four processing parameters: the hot pressing temperature, the soaking time, the applied pressure and SiC content. In this way, an L9 orthogonal array, including nine experiments for four parameters with three levels, was used to optimize the processing factors. The analysis of variance identified the applied pressure as the most impressive parameter affecting the densification and hardness of ZrB 2-SiC composites. A relative density of~96% and a Vickers hardness of 15.2 GPa were achieved for ZrB 2-25 vol.% SiC composite with the sintering temperature of 1850°C, the soaking time of 90 min and the applied pressure of 16 MPa. The confirmation test, fulfilled under the optimal conditions, disclosed that the result of the experiment and the Taguchi prediction were alike.
A Processing–Microstructure Correlation in ZrB2–SiC Composites Hot-pressed under a Load of 10 MPa
Universal Journal of Materials Science, 2015
Monolithic ZrB 2 ceramic and its composites, with 5 to 30 vol. % SiC, has been prepared by hot pressing at temperatures of 1700, 1850 and 2000 °C, for 30 minutes under relatively low pressure of 10 MPa. Densification behavior of ZrB 2-based composites is improved by the addition of SiC particulates. The fracture surface of monolithic ZrB 2 ceramics shows a grained structure, with faceted ZrB 2 grains, as the fracture appears to spread prevalently along an intergranular path. The ZrB 2 /ZrB 2 boundary interface is seemingly free of any secondary phases. The microstructure of ZrB 2-30 vol. % SiC composite, hot-pressed at 1700 °C, is consistent with measured porosity for the sample that has ~8% open pores, nearly without closed pores. It seems that mechanical interlocking between ZrB 2 and SiC is an important mechanism for densification. In the microstructure of specimens consolidated at 1850 °C, neck formation between ZrB 2 particles is visible. In contrast, relatively fully dense samples are obtained by hot-pressing at 2000 °C. Intergranular SiC particles inside ZrB 2 grains show the occurrence of mass transfer among ZrB 2 particles, which in effect brings the elimination of pores to a fortunate ending. Efficient mixing of starting powders is very critical in order to achieve a fine-grained homogenous microstructure.
Hardness and toughness of hot pressed ZrB2–SiC composites consolidated under relatively low pressure
Journal of Alloys and Compounds, 2015
ZrB 2-based composites, containing 15, 20, 25, and 30 vol% SiC, have been prepared by hot pressing at temperatures of 1700, 1850 and 2000°C for 30 min under a relatively low pressure of 10 MPa. Densification and mechanical properties of ZrB 2-SiC composites have been investigated. Fully dense ZrB 2-30 vol% SiC composite with a relative density of 99.8% is obtained at 2000°C. The highest values of Vickers hardness (21.3 GPa) and fracture toughness (4.7 MPa m 1/2) belong to this sample. Vickers hardness increases exponentially as the relative density of composite increases. A simplified equation was developed for the Vickers hardness of the investigated ZrB 2-SiC composites as a function of relative density and SiC content. Microstructural investigation by means of optical and scanning electron microscopy shows that by addition of SiC particles, some toughening mechanisms such as crack deflection, crack branching, microcracking, crack bridging, break of large SiC grains, and crack arresting by porosity are appeared.
Role of h-BN content on microstructure and mechanical properties of hot-pressed ZrB2–SiC composites
Ceramics International, 2020
The addition of h-BN flacks (0-35 vol%) into the ZrB 2-SiC composites was investigated in the present research. The composites were consolidated at a temperature of 1800°C for 1 h under 40 MPa uniaxial pressure by a hotpressing facility. The properties of the composites, such as density, hardness, bending strength, the microstructure, and phase evolution, were evaluated with various contents of h-BN. Densification of the hot-pressed composites improved by the addition of BN, as a nearly full densification was achieved by adding 2.5 vol% BN. X-ray diffraction analysis disclosed the formation of the Zr 3 N 4 , B 4 C, and SiCN phases in the as-sintered triplet composites. The highest bending strength of 350 MPa was obtained for the composite containing 2.5 vol% BN. Due to the poor sinterability of boron nitride flakes, the addition of higher amounts of h-BN (> 5 vol%) dramatically decreased the bending strength and Vickers hardness.
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.