Investigation of Effective Parameters on Densification of ZRB2-SIC Basedcomposites Using Taguchi Method (original) (raw)
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Materials Chemistry and Physics, 2017
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 open porosity respectively.
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.
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.
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...
Ceramics International, 2015
ZrB 2-25 vol% SiC ceramic composites were prepared by hot pressing in order to investigate the effects of processing parameters and SiC particle size (20 nm, 200 nm and 5 mm) on the densification behavior. At this study, an experimental design technique (Taguchi method) was used to specify the significance of four factors and to obtain the optimal conditions. The statistical analysis distinguished the applied pressure as the most effective parameter on the relative density of ZrB 2-SiC composites. A relative density of $100% was obtained at the optimal processing conditions: temperature of 1850 1C, holding time of 90 min, pressure of 16 MPa and SiC particle size of 200 nm. The confirmation test, performed under optimum conditions, indicated that the experimental outcomes were equal with the expected values from the Taguchi prediction. The mechanisms of enhanced densification of hot pressed ZrB 2-SiC ceramic composites were discussed.
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.
Fractographical assessment of densification mechanisms in hot pressed ZrB2-SiC composites
The controlling densification mechanisms of hot pressed monolithic ZrB2 ceramics and ZrB2-based composites, containing 15 and 30 vol. % SiC, at different consolidating temperatures were investigated, based on scanning electron microscopy micrographs of fracture surfaces, relative densities, and average grain size of ZrB2. For the hot pressed samples at 1700 °C, particles fragmentation in the composite samples, mechanical interweaving, and rearrangement without sizeable chemical bonding were appointed as dominant densification mechanisms. Neck formation between ZrB2/ZrB2 was observed at 1850 °C and plastic deformation of ZrB2 grains were nominated as controlling densification mechanisms. Reduction of porosity in the hot pressed specimens at 2000 °C was related to grain boundary diffusion mechanism. Colossal grain growth in monolithic ZrB2 ceramic proposed the occurrence of detrimental mechanisms such as grain coarsening and evaporation/condensation. Presence of intergranular SiC particles between ZrB2 grains impeded extremist grain growth.
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.
Effect of open porosity on flexural strength and hardness of ZrB2-based composites
Ceramics International, 2015
In this work, Taguchi L32 experimental design was applied to optimize flexural strength and hardness of ZrB2-based composites which were prepared by SPS. With this aim, batch ZrB2based composites tests were performed to achieve targeted experimental design with nine factors (SiC, Cf, MoSi2, HfB2 and ZrC content, milling time of Cf and SPS parameters such as temperature, time and pressure) at four different levels. Flexural strength of all composites was measured by three-point bending test. Hardness measurement was done by Vickers indenter. SEM was applied to evaluate microstructure. The results showed that SiC grain size plays important role on flexural strength and correlation between flexural strength and open porosity is low while hardness strongly depends to open porosity. Grain size variation in the range of ~ 1.5 µm to ~ 8 µm has little effect on hardness.