Optimization of effective parameters on thermal shock resistance of ZrB 2 -SiC-based composites prepared by SPS: Using Taguchi design (original) (raw)
Related papers
2016
The main goal of this study is optimization of densification of ZrB2-SiC composites reinforced with chopped Cf prepared by SPS. Taguchi method is employed as statistical design of experiment (DOE) to optimize densification parameters including SiC, Cf, MoSi2, HfB2 and ZrC content, milling time of Cf and SPS parameters such as temperature, time and pressure. Each of these factors was examined on four levels in order to obtain the optimum conditions. A total of 32 samples were prepared in accordance to the L32 array proposed by the Taguchi method. By using statistical analysis of variance (ANOVA), it has been concluded that the most significant effect on the densification is related to temperature, MoSi2 and time by 50.2%, 20.7% and 9.8% portion, respectively. Also, the results showed that pressure with 0.8%, ZrC with 1.9% and HfB2 with 1.9% portion have the least effect on open porosity. The other parameters including SiC, milling time (M.t) and Cf have 2.9%, 3.6% and 3.8% portion on...
Ceramics International, 2017
In this work, Taguchi experimental design technique was applied to determine the most influential additives and SPS parameters for optimizing fracture toughness of ZrB 2-SiC based composites. In this case, nine factors (SiC, C f , MoSi 2 , HfB 2 and ZrC content, milling time of C f and SPS parameters such as temperature, time and pressure) were examined on four different levels in order to obtain the optimum mixture. A total of 32 mixtures were prepared in accordance to the L32 array proposed by the method. Fracture toughness of all composites was measured by single edge-notch beam test. SEM was applied to evaluate microstructure. It has been concluded that the open porosity up to 10% has no significant effect on fracture toughness but in higher values, it is varied inversely with its changes. The results showed that temperature with 34.7% and SiC with 29.7% have significant effect on fracture toughness. C f , M.t, HfB 2 , pressure and time with 2.3%, 3.2%, 0.05%, 0.44% and 2.3% have influence on fracture toughness, respectively. ZrC has 7.8% and MoSi 2 has 6.3% on fracture toughness.
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.
Ceramics International, 2013
The effect of SiC content, additives, and process parameters on densification and structure-property relations of pressureless sintered ZrB 2 -(10-40 vol%) SiC particulate composites have been studied. The ZrB 2 -SiC composite powders mixed by ball-milling with 1.2 wt% C (added as phenolic resin) and 3 wt% B 4 C have been uniaxially cold-compacted and sintered in argon environment at 1950-2050 1C for 2 h, or at 2000 1C for durations between 1/2 and 3 h. The amount of densification is found to increase with sintering duration, and by prior holding at 1250 and 1600 1C for reduction of oxide impurities (ZrO 2 , B 2 O 3 and SiO 2 ) on powder particle surfaces by the aforementioned additives. Presence of SiC with average size smaller than that of ZrB 2 appears to aid in densification by enhancing green density, increasing WC content by erosion of milling media, and inhibiting matrix grain growth. Both SiC and WC appear to aid in reduction of oxide impurities. Furthermore, the impurities enriched in W, Fe and Co obtained from milling media are found to be segregated at ZrB 2 grain boundaries, and appear to assist in densification by forming liquid phase, which completely wets the ZrB 2 grains. Hardness increases with SiC content or with sintering duration till 1 h, but decreases for periods Z2 h due to grain growth. The experimentally measured elastic moduli approaches corresponding theoretically predicted values with increasing SiC content due to reduction in porosity.
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.
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...
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.
Chemical Engineering Journal, 2014
Fine grained ZrB 2 -SiC-hBN composite were reactively densified from coarse precursors. Employ the SHS ignited in ZrN-Si-B 4 C systems to improve microstructure homogeneity. Strength reliability and strain tolerance of obtained ceramics were much improved. a b s t r a c t A novel top down approach was developed to fabricate dense ZrB 2 -SiC-BN (ZSN) composites with a finegrained (<1 lm) microstructure using coarse-grained ($10 lm) ZrN and Si precursors that reacted with fine ($0.5 lm) B 4 C powders at 1850°C. The results show that the ''reaction'' and ''densification'' mechanisms acting during sintering could be separated or happen simultaneously by changing the pressure loading strategy. Loading cycles not only have a substantial influence on the microstructure homogeneity and the strength reliability of as sintered composites, but might alter the electric current path during the Spark Plasma Sintering process as well. A residual compressive stress of 361 MPa, generated upon the SiC grains in the ZSN composites, was measured by Raman spectroscopy. The fine SiC grains tended to form larger clusters in the dense microstructure if the loading cycle is inappropriate, which was further employed to interpret the observed scattering of strength values in one batch of ZSN. The 48ZrB 2 -24SiC-28BN (number in vol%) composite has an average strength of 473 MPa, which was 94% of that of in situ densified ZrB 2 -SiC ceramics (ZS). Considering the corresponding Younǵ s modulus was only half of that for ZS, the in situ ZSN composite owns a better mechanical strain tolerance.