SiC chopped fibers reinforced ZrB2: Effect of the sintering aid (original) (raw)
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Effect of Milling on the Mechanical Properties of Chopped SiC Fiber-Reinforced ZrB2
Materials, 2013
This work aims at studying the effect of the milling conditions on the microstructure and mechanical properties of a ZrB 2 -5 vol% Si 3 N 4 matrix reinforced with chopped Hi-Nicalon SiC fibers. Several composites were obtained using different milling conditions in terms of time, speed and type of milling media. The composites were prepared from commercial powders, ball milled, dried and shaped, and hot pressed at 1720 °C. Their relative bulk densities achieved values as high as 99%. For each material the fiber length distribution, the extent of reacted fiber area and matrix mean grain size were evaluated in order to ascertain the effects of milling time, milling speed and type of milling media. While the fracture toughness and hardness were statistically the same independently of the milling conditions, the flexural strength changed. From the results obtained, the best milling conditions for optimized mechanical properties were determined.
Combined effect of SiC chopped fibers and SiC whiskers on the toughening of ZrB2
2014
ZrB 2 -based composites were toughened by the simultaneous additions of SiC chopped fibers and SiC whiskers. The fracture toughness measured by Chevron Notched Beam in flexure was of the order of 6 MPa m 1/2 and the 4-pt flexural strength around 500 MPa. The values of mechanical properties are compared to those of unreinforced ZrB 2 and composites reinforced by solely fibers or whiskers in order to understand whether a synergistic whiskers-fibers toughening action is present or not in these composites. The combination of two different reinforcing agents is a successful strategy to obtain a super reinforcement provided that densification, reinforcing agents chemical integrity and secondary phases composition and amount are properly controlled.
Toughened ZrB2-based ceramics through SiC whisker or SiC chopped fiber additions
2010
In order to improve the fracture toughness, SiC whiskers or SiC chopped fibers were added to a ZrB 2 matrix in volumetric fraction of 10 and 20 vol.%. The composites were hot-pressed between 1650 and 1730 • C and their final relative densities were higher than 95%. Even at the lowest sintering temperature, the whiskers showed an evident degradation. On the other hand, the fibers maintained their initial shape and a strong interface formed between matrix and reinforcement. The fracture toughness of the composites increased from 30 to 50% compared to the baseline material, with the fibers showing a slightly higher toughening effect. In the whiskers-reinforced composites, the room-temperature strength increased when 10 vol.% whiskers were added. In the fibers-reinforced composites, the room-temperature strength decreased regardless the amount of fibers added. The high-temperature strength of the composites was higher than that of the baseline material for both types of reinforcement.
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.
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.
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.
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.
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...