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1.
Pressureless Sintering of Zirconium Diboride Using Boron Carbide and Carbon Additions 总被引:1,自引:0,他引:1
Sumin Zhu William G. Fahrenholtz Gregory E. Hilmas Shi C. Zhang 《Journal of the American Ceramic Society》2007,90(11):3660-3663
The synergistic roles of boron carbide and carbon additions in the enhanced densification of zirconium diboride (ZrB2 ) by pressureless sintering have been studied. ZrB2 was sintered to >99% relative density at 1900°C. The combination of 2 wt% boron carbide and 1 wt% carbon promoted densification by removing surface oxide impurities (ZrO2 and B2 O3 ) and inhibiting grain growth. Four-point bending strength (473±43 MPa), Vickers' microhardness (19.6±0.4 GPa), fracture toughness (3.5±0.6 MPa·m1/2 ), and Young's modulus (507 GPa) were measured. Thermal gravimetry showed that the combination of additives did not have an adverse effect on the oxidation behavior. 相似文献
2.
Pressureless Sintering of Zirconium Diboride 总被引:3,自引:0,他引:3
Adam L. Chamberlain William G. Fahrenholtz Gregory E. Hilmas 《Journal of the American Ceramic Society》2006,89(2):450-456
Zirconium diboride (ZrB2 ) ceramics were sintered to a relative density of ∼98% without applied external pressure. Densification studies were performed in the temperature range of 1900°–2150°C. Examination of bulk density as a function of temperature revealed that shrinkage started at ∼2100°C, with significant densification occurring at only 2150°C. At 2150°C, isothermal holds were used to determine the effect of time on relative density and microstructure. For a hold time of 540 min at 2150°C, ZrB2 pellets reached an average density of 6.02±0.04 g/cm3 (98% of theoretical) with an average grain size of 9.0±5.6 μm. Four-point bend strength, elastic modulus, and Vickers' hardness were measured for sintered ZrB2 and compared with values reported for hot-pressed materials. Vickers' hardness of sintered ZrB2 was 14.5±2.6 GPa, which was significantly lower when compared with 23 GPa for hot-pressed ZrB2 . Strength and elastic modulus of the ZrB2 were 444±30 MPa and 454 GPa, which were comparable with values reported for hot-pressed ZrB2 . The ability to densify ZrB2 ceramics without hot pressing should enable near-net shape processing, which would significantly reduce the cost of fabricating ZrB2 components compared with conventional hot pressing and machining. 相似文献
3.
Pressureless Sintering of Boron Carbide 总被引:4,自引:0,他引:4
B4 C powder compacts were sintered using a graphite dilatometer in flowing He under constant heating rates. Densification started at 1800°C. The rate of densification increased rapidly in the range 1870°–2010°C, which was attributed to direct B4 C–B4 C contact between particles permitted via volatilization of B2 O3 particle coatings. Limited particle coarsening, attributed to the presence or evolution of the oxide coatings, occurred in the range 1870°–1950°C. In the temperature range 2010°–2140°C, densification continued at a slower rate while particles simultaneously coarsened by evaporation–condensation of B4 C. Above 2140°C, rapid densification ensued, which was interpreted to be the result of the formation of a eutectic grain boundary liquid, or activated sintering facilitated by nonstoichiometric volatilization of B4 C, leaving carbon behind. Rapid heating through temperature ranges in which coarsening occurred fostered increased densities. Carbon doping (3 wt%) in the form of phenolic resin resulted in more dense sintered compacts. Carbon reacted with B2 O3 to form B4 C and CO gas, thereby extracting the B2 O3 coatings, permitting sintering to start at ∼1350°C. 相似文献
4.
Jie Yin Zhaoquan Zhang Zhengren Huang Hui Zhang Yongjie Yan Xuejian Liu Yan Liu Dongliang Jiang 《International Journal of Applied Ceramic Technology》2014,11(6):1039-1044
Dense (97.3%) zirconium diboride (ZrB2) ceramics were obtained via gelcasting and pressureless sintering. Four wt% B4C was used as sintering aid. ZrB2, SiC, and B4C can codisperse well in the alkaline region, using a polyacrylate dispersant. Compared with monolithic ZrB2 (Z), the mechanical properties of ZrB2‐SiC (ZS) were enhanced. The Vickers hardness and fracture toughness of ZS were (13.1 ± 0.6) GPa and (2.5 ± 0.4) MPa m1/2, respectively. 相似文献
5.
Kathy Lu Xiaojing Zhu Karthik Nagarathnam 《Journal of the American Ceramic Society》2009,92(7):1500-1505
Sintering of pure B4 C and Ni2 B nanolayer-coated B4 C was studied from 1300° to 1600°C, with the holding time at the peak temperatures being 2 or 10 h. Compacts were made by uniaxial die compaction and combustion-driven compaction. Pure B4 C sample shows less sintering at all conditions. Ni2 B-coated B4 C sample shows more extensive densification, neck formation, and grain shape accommodation. The combustion driven compaction process accelerates sintering by offering higher green density to start with. The Ni2 B species on the B4 C particle surfaces melts into a nickel–boron-containing liquid phase during heating, remains as liquid during sintering, and then transforms into Ni4 B3 and NiB during cooling. High-resolution composition analysis shows that there is no nickel diffusion into bulk B4 C during the sintering process. However, there is boron diffusion into the Ni2 B coating layer. Carbon diffusion cannot be directly measured but is believed to be a simultaneous process as boron diffusion. A multievent sintering process has been proposed to explain the observations. 相似文献
6.
Effect of Iron and Boron Carbide on the Densification and Mechanical Properties of Titanium Diboride Ceramics 总被引:4,自引:0,他引:4
Eul Son Kang Cheol Woo Jang Chae Hyun Lee Chong Hee Kim Do Kyung Kim 《Journal of the American Ceramic Society》1989,72(10):1868-1872
The effect of Fe and B4 C on the sintering behavior and mechanical properties of TiB2 ceramics have been studied. Sintering was performed in an Ar atmosphere at 2000° using attrition-milled TiB2 powder (mean particle size = 0.8 μm). When a small amount of Fe (0.5 wt%) was added, abnormal grain growth occurred and the sintered density was low. In the case of B4 C added along with 0.5 wt% Fe, however, abnormal grain growth was remarkably suppressed, and the sintered density was increased up to 95% of theoretical. But with excess Fe addition (5 wt%), B4 C grains did not act as a grain growth inhibitor, and B4 C grains were frequently trapped in large TiB2 grains. The best mechanical properties were obtained for the TiB2 –10 wt% B4 C–0.5 wt% Fe ceramics, which exhibited a three-point bending strength of 400 MPa and a fracture toughness of 5.5 MPa · m1/2 . 相似文献
7.
Low-Temperature Densification of Zirconium Diboride Ceramics by Reactive Hot Pressing 总被引:2,自引:1,他引:1
Adam L. Chamberlain William G. Fahrenholtz Gregory E. Hilmas 《Journal of the American Ceramic Society》2006,89(12):3638-3645
Zirconium diboride–silicon carbide ceramics with relative densities in excess of 95% were produced by reactive hot pressing (RHP) at temperatures as low as 1650°C. The ZrB2 matrix was formed by reacting elemental zirconium and boron. Attrition milling of the starting powders produced nanosized (<100 nm) Zr particulates that reacted with B below 600°C. The reaction resulted in the formation of nanoscale ZrB2 crystallites that could be densified more than 250°C below the temperatures required for conventional ZrB2 powder. Because of the low-temperature densification, the resulting ZrB2 grain sizes were as small as 0.5±0.30 μm for specimens densified at 1650°C and 1.5±1.2 μm for specimens densified at 1800°C. Vickers hardness, elastic modulus, and flexure strength of fully dense materials produced by RHP were 27, 510, and 800 MPa, respectively. 相似文献
8.
William G. Fahrenholtz Gregory E. Hilmas Shi C. Zhang Sumin Zhu 《Journal of the American Ceramic Society》2008,91(5):1398-1404
Zirconium diboride (ZrB2 ) was densified by pressureless sintering using <4-wt% boron carbide and/or carbon as sintering aids. As-received ZrB2 with an average particle size of ∼2 μm could be sintered to ∼100% density at 1900°C using a combination of boron carbide and carbon to react with and remove the surface oxide impurities. Even though particle size reduction increased the oxygen content of the powders from ∼0.9 wt% for the as-received powder to ∼2.0 wt%, the reduction in particle size enhanced the sinterability of the powder. Attrition-milled ZrB2 with an average particle size of <0.5 μm was sintered to nearly full density at 1850°C using either boron carbide or a combination of boride carbide and carbon. Regardless of the starting particle size, densification of ZrB2 was not possible without the removal of oxygen-based impurities on the particle surfaces by a chemical reaction. 相似文献
9.
Tamoghna Chakrabarti Lingappa Rangaraj Vikram Jayaram 《Journal of the American Ceramic Society》2014,97(10):3092-3102
Densification mechanisms involved during reactive hot pressing (RHP) of zirconium carbide (ZrC) have been studied. RHP has been carried out using zirconium (Zr) and graphite (C) powders in the molar ratios 1:0.5, 1:0.67, 1:0.8, and 1:1 at 40 MPa, 800°C–1200°C for different durations. The volume fractions of phases formed, including porosity, are determined from the measured density and from Rietveld analysis. Increased densification with an increasing nonstoichiometry in carbon has been observed. Microstructural and X‐ray diffraction observations coupled with the predictions of a model based on the constitutive laws governing plastic flow of zirconium suggest that the better densification of nonstoichiometric compositions arise from the higher amount of starting Zr and also the longer duration of its availability for plastic flow during RHP. Volume shrinkage due to reaction between Zr and C and the gradual elimination of the soft metal phase limit the final density achievable. Based on these observations, a two‐step RHP carried out at 800°C and 1200°C leads to a better densification than a single RHP at 1200°C. 相似文献
10.
Matiur Rahman Ching C. Wang Weihua Chen Sheikh A. Akbar Cathleen Mroz 《Journal of the American Ceramic Society》1995,78(5):1380-1382
The electrical resistivities of hot-pressed samples of Ti1- x Zr x B2 ( x = 0.0, 0.3, 0.5, 0.7, 1.0) were measured by a four-point ac technique over the range 298 to 1573 K in an argon atmosphere. The hot-pressed samples for the intermediate compositions were found to be mixtures of two solid-solution phases. The resistivities for all compositions were found to increase linearly with temperature and can be described by ρ( T ) =ρ298 +φ( T - 298). The room-temperature resistivity ρ298 (μΩ cm) and the temperature coefficient of resistivity φ (nΩ·cm/K) for ZrB2 were determined to be 7.8 and 10, both of which increase with the content of TiB2 . These values for TiB2 were determined to be 20.4 and 36, respectively. 相似文献
11.
Jason M. Lonergan William G. Fahrenholtz Greg E. Hilmas 《Journal of the American Ceramic Society》2014,97(6):1689-1691
Thermal properties were characterized for zirconium diboride produced by reactive hot pressing and compared to ZrB2 ceramics that were hot pressed from commercial powders. No sintering additives were used in either process. Thermal conductivity was calculated from measured values of heat capacity, thermal diffusivity, and density for temperatures ranging from 298 to 2273 K. ZrB2 produced by reactive hot pressing achieved near full density, but had a small volume fraction of ZrO2, whereas hot‐pressed ZrB2 contained porosity and carbon inclusions. Reactive hot pressing produced a ceramic with higher thermal diffusivity and heat capacity, resulting in thermal conductivities of 127 W·(m·K)?1 at 298 K and 80 W·(m·K)?1 at 2273 K, which were up to ~30% higher than typically reported for hot‐pressed ZrB2. 相似文献
12.
Gregory J. K. Harrington Greg E. Hilmas William G. Fahrenholtz 《Journal of the American Ceramic Society》2013,96(11):3622-3630
The role of carbon additions and oxygen content on the densification of zirconium diboride (ZrB2) was studied. ZrB2 with up to 1 wt% added carbon was hot pressed at temperatures of 2000°C and 2100°C. Nominally pure ZrB2 hot pressed at 2100°C achieved relative densities >95.5%. Carbon and oxygen analysis indicate that oxygen removal was facilitated by the reduction of oxides with carbon or the removal of boria (B2O3) as a vapor. Therefore, by removing oxides from the particle surfaces, carbon additions of ≥0.5 wt% enabled densification to proceed to >96.5% of theoretical at 2000°C. Raman spectroscopy revealed the formation of boron carbide (B4.3C) in specimens with carbon additions of ≥0.75 wt%. The formation of B4.3C was eliminated via a 1 wt% addition of zirconium hydride (ZrH2), as a source of zirconium, resulting in the formation of carbon as the only residual second phase. Grain sizes were in the range of 7–10 μm (2000°C) and 12–16 μm (2100°C) and only appeared to be controlled by temperature, as no trends due to the evaluated carbon or oxygen contents were observed. 相似文献
13.
Si3 N4 test bars containing additions of BN, B4 C, and C, were hot isostatically pressed in Ta cladding at 1900° and 2050°C to 98.9% to 99.5% theoretical density. Room-temperature strength data on specimens containing 2 wt% BN and 0.5 wt% C were comparable to data obtained for Si3 N4 sintered with Y2 O3 , Y2 O3 and Al2 O3 , or ZrO2 . The 1370°C strengths were less than those obtained for additions of Y2 O3 or ZrO2 but greater than those obtained from a combination of Y2 O3 and Al2 O3 . Scanning electron microscope fractography indicated that, as with other types of Si3 N4 , roomtemperature strength was controlled by processing flaws. The decrease in strength at 1370°C was typical of Si3 N4 having an amorphous grainboundary phase. The primary advantage of non-oxide additions appears to be in facilitating specimen removal from the Ta cladding. 相似文献
14.
Carmen M. Carney Pavel Mogilvesky Triplicane A. Parthasarathy 《Journal of the American Ceramic Society》2009,92(9):2046-2052
Dense samples of ZrB2 –20 vol% SiC were successfully fabricated by spark plasma sintering without the use of sintering aids. Oxidation behavior of these samples was characterized by exposing them to 1400°, 1500°, and 1600°C in an ambient atmosphere for 150 min, and by measuring the weight gains of the sample and crucible, as well as the thickness of the oxide scale and the glassy outer layer. The effects of gravity on the viscous outer layer are shown to result in significant heterogeneity within a sample. The oxidation scales were characterized by scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy analysis. The oxide scale was found to be composed of three layers: (1) a SiO2 -rich glassy outer layer, (2) an intermediate layer of a ZrO2 matrix with interpenetrating SiO2 , and (3) a layer containing a ZrO2 matrix enclosing partially oxidized ZrB2 with Si–C–B–O glass inclusions. 相似文献
15.
Xianwu Du Zhixiao Zhang Yang Wang Jilin Wang Weimin Wang Hao Wang Zhengyi Fu 《Journal of the American Ceramic Society》2015,98(5):1400-1406
The hot‐pressing kinetics of boron carbide at different stages in the hot‐pressing process was investigated. Based general densification equation and pore‐dragged creep model, the densification and grain growth kinetics were analyzed as a function of various parameters such as sintering temperature, sintering pressure and dwell time. Stress exponent of n ≈ 3 at the initial dwell stage suggests the plastic deformation may dominates the densification. The further TEM observations and the calculation based on effective stress and plastic yield stress also indicate that plastic deformation may occur and account for the large increase in density at the initial stage of sintering. Calculated grain size exponent of m ≈ 3 suggests that the grain‐boundary diffusion dominates the densification at the final stage. During the final stage of sintering, grain growth may be determined by evaporation/condensation and grain‐boundary migration. 相似文献
16.
The microstructure of a ZrB2 -platelet-reinforced ZrC x composite was examined using transmission electron microscopy and X-ray diffraction. The composites, which are formed by the reaction of molten Zr with B4 C, contain a small amount of residual Zr, the amount of which can be varied by altering the processing conditions. Results on two different materials are reported, one with a low Zr content, ∼2.5 vol%, and the other with a very low Zr content, ∼0.5 vol%. In the former, metallic Zr was found at triple points and as a grain boundary phase between the boride and carbide, and to a lesser degree between the boride grains. In the latter, it was only found as a ternary Zr–ZrB2 –ZrC x eutectic at the triple points. Both materials showed a nearly random distribution of the boride and carbide constituents, though specific crystallographic relationships were found between the various constituents. 相似文献
17.
Zhihui Lü Dongliang Jiang Jingxian Zhang Qingling Lin 《Journal of the American Ceramic Society》2009,92(10):2212-2217
Aqueous tape casting of ZrB2 powder with sintering additives was investigated. The dispersion of ZrB2 suspensions in aqueous media was studied and characterized in terms of zeta potential, sedimentation, and rheological measurements. A well-stabilized suspension with a high solid content (up to 45 vol%) was prepared in the alkaline pH region with 0.4 wt% Lopon 885 as the dispersant. Several suspensions with different compositions of binder and plasticizer were prepared for comparison. Crack-free green tapes with a maximum thickness of approximately 250 μm were obtained with a binder content of 18–23 wt%. The green tapes had high qualities, such as homogeneity, good flexibility, and a smooth surface. Results showed that the slurries at selected formulations met the needs of the tape-casting process. 相似文献
18.
Adrian Goldstein Ygal Geffen Ayala Goldenberg 《Journal of the American Ceramic Society》2001,84(3):642-644
The heating of B4 C–YTZP (where YTZP denotes yttria-stabilized zirconia polycrystals) mixtures, under an argon atmosphere, generates B4 C–ZrB2 composites, because of a low-temperature (<1500°C) carbide–oxide reaction. Composites derived from mixtures that include ≥15% YTZP are better sintered than monolithic B4 C that has been fired under the same conditions. Firing to ∼2160°C (1 h dwell) generates specimens with a bulk density of ≥91% of the theoretical density (TD) for cases where the initial mixture includes ≥15% YTZP. Mixtures that include 30% YTZP allow a fired density of ≥97.5% TD to be attained. The behavior of the B4 C–YTZP system is similar to that of the B4 C–TiO2 system. Dense B4 C–ZrB2 composites attain a hardness (Vickers) of 30–33 GPa. 相似文献
19.
20.
《中国耐火材料》2019,(4)
The oxidation behaviors of fused zirconium diboride and chemosynthetic zirconium diboride as well as morphology and composition of their oxidation products were researched by FESEM-EDS and XRD. The two kinds of zirconium diboride were heated at 700 ℃, 900 ℃, 1 100 ℃ and 1 300 ℃ for 3 h in air, respectively. The results show that ZrO_2 and B_2O_3(l) are generated from the chemosynthetic zirconium diboride oxidized at 700 ℃ for 3 h or the fused zirconium diboride oxidized at 800 ℃ for 24 h; B_2O_3(l) dissolves into water and then H_3BO_3 crystallizes. 相似文献