High‐Strength B4C–TaB2 Eutectic Composites Obtained via In Situ by Spark Plasma Sintering

The in situ synthesis/consolidation of B₄C–TaB₂ eutectic composites by spark plasma sintering (SPS) is reported. Samples for the evaluation of bending strength were cut from specimens with diameters of 30 mm. The sample prepared for the three‐point flexural strength test had fibers of tantalum diboride with diameter of 1.3 ± 0.4 μm distributed in the B₄C matrix, thereby reducing composites brittleness and yielding an indentation fracture toughness of up to 4.5 MPa·m^1/2. Furthermore, the Vickers hardness of B₄C–TaB₂ eutectics formed by SPS was as high as 26 GPa at an indentation load of 9.8 N. The flexural strength of the B₄C–TaB₂ system has been reported for the first time. Some steps were identified in the load–displacement curve, suggesting that micro‐ and macrocracking occurred during the flexural test. Ceramic composites with a eutectic structure exhibited a room‐temperature strength of 430 ± 25 MPa. Compared with other eutectic composites of boron carbide with transition‐metal diborides, room‐temperature strength the B₄C–TaB₂ was 40% higher than that of B₄C–TiB₂ ceramics, demonstrating advantage of the in situ synthesis/consolidation of eutectic composites by SPS.     

Plasma Processing of B4C–TiB2 Eutectic Composite Powders

The production of a composite powder of eutectic B₄C–TiB₂ is demonstrated via an atmospheric plasma processing method. Feedstock material is prepared for plasma processing by mixing and spray drying monolithic B₄C and TiB₂ to produce a flowable precursor powder. These powders are fed through a plasma torch, where they are melted and actively quenched in flight with argon gas. Plasma processed powders are composed of crystalline B₄C and TiB₂, with some additional B₂O₃ oxide phase. The plasma processing method results in the production of monolithic B₄C and TiB₂ nanoparticles, but some larger particles (generally ≥10 μm in diameter) are shown to contain the traditional lamellar eutectic microstructure. The eutectic interphase spacing ranges from 100 to 650 nm, and the composite microstructure is present through the entire thickness of the eutectic particles. Future work on plasma processing of eutectic powders should focus on methods utilizing passive in‐flight quenching to increase the average particle size.     

Spark Plasma Sintering of Superhard B4C–ZrB2 Ceramics by Carbide Boronizing

A carbide boronizing method was first developed to produce dense boron carbide‐ zirconium diboride (“B₄C”–ZrB₂) composites from zirconium carbide (ZrC) and amorphous boron powders (B) by Spark Plasma Sintering at 1800°C–2000°C. The stoichiometry of “B₄C” could be tailored by changing initial boron content, which also has an influence on the processing. The self‐propagating high‐temperature synthesis could be ignited by 1 mol ZrC and 6 mol B at around 1240°C, whereas it was suppressed at a level of 10 mol B. B₈C–ZrB₂ ceramics sintered at 1800°C with 1 mole ZrC and 10 mole B exhibited super high hardness (40.36 GPa at 2.94 N and 33.4 GPa at 9.8 N). The primary reason for the unusual high hardness of B₈C–ZrB₂ ceramics was considered to be the formation of nano‐sized ZrB₂ grains.     

放电等离子烧结制备Ti/Al2O3复合材料

Ti基金属复合材料是一种新型高温结构材料.本文利用放电等离子烧结技术,在温度1250℃、压力30MPa、真空度6Pa,保温时间10min条件下,制备了相对致密度较高的Ti/Al2O3复合材料.借助XRD,SEM,EDS等测试手段对该复合材料的物相组成、界面反应、微观结构以及致密度进行了观察与分析.结果表明:利用SPS技术制备Ti/Al2O3的复合材料,晶粒细小且分布均匀,结构致密、2相之间结合状态良好,相对致密度随材料中陶瓷相含量的增多而有所降低.Ti,Al2O32相之间无明显界面化学反应发生.     

ZrB2–SiC–G Composite Prepared by Spark Plasma Sintering of In‐Situ Synthesized ZrB2–SiC–C Composite Powders

To avoid introduction of milling media during ball‐milling process and ensure uniform distribution of SiC and graphite in ZrB₂ matrix, ultrafine ZrB₂–SiC–C composite powders were in‐situ synthesized using inorganic–organic hybrid precursors of Zr(OPr)₄, Si(OC₂H₅)₄, H₃BO₃, and excessive C₆H₁₄O₆ as source of zirconium, silicon, boron, and carbon, respectively. To inhabit grain growth, the ZrB₂–SiC–C composite powders were densified by spark plasma sintering (SPS) at 1950°C for 10 min with the heating rate of 100°C/min. The precursor powders were investigated by thermogravimetric analysis–differential scanning calorimetry and Fourier transform infrared spectroscopy. The ceramic powders were analyzed by X‐ray diffraction, X‐ray photoelectron spectroscopy, and scanning electron microscopy. The lamellar substance was found and determined as graphite nanosheet by scanning electron microscopy, Raman spectrum, and X‐ray diffraction. The SiC grains and graphite nanosheets distributed in ZrB₂ matrix uniformly and the grain sizes of ZrB₂ and SiC were about 5 μm and 2 μm, respectively. The carbon converted into graphite nanosheets under high temperature during the process of SPS. The presence of graphite nanosheets alters the load‐displacement curves in the fracture process of ZrB₂–SiC–G composite. A novel way was explored to prepare ZrB₂–SiC–G composite by SPS of in‐situ synthesized ZrB₂–SiC–C composite powders.     

放电等离子烧结工艺制备Ti_2AlC材料的研究

以元素粉钛、铝、碳为原料 ,采用放电等离子烧结工艺在 1 1 0 0℃的温度下成功地制备了高纯、致密Ti2 AlC材料。合成材料的X -射线衍射 (XRD)和扫描电镜 (SEM)分析的结果表明 :多晶体Ti2 AlC形貌为板状结晶 ,晶粒大小平均约为 2 0 μm ,厚度在 3～ 5 μm。     

放电等离子烧结工艺制备Ti2A1C材料的研究

以元素粉钛、铝、碳为原料,采用放电等离子烧结工艺在1100℃的温度下成功地制备了高纯、致密Ti2AlC材料.合成材料的X-射线衍射(XRD)和扫描电镜(SEM)分析的结果表明:多晶体Ti2AlC形貌为板状结晶,晶粒大小平均约为20μm,厚度在3～5μm.     

Boron Carbide–Zirconium Boride In Situ Composites by the Reactive Pressureless Sintering of Boron Carbide–Zirconia Mixtures

The heating of B₄C–YTZP (where YTZP denotes yttria-stabilized zirconia polycrystals) mixtures, under an argon atmosphere, generates B₄C–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 B₄C 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 B₄C–YTZP system is similar to that of the B₄C–TiO₂ system. Dense B₄C–ZrB₂ composites attain a hardness (Vickers) of 30–33 GPa.     

Crystallization of Eutectic Structures in the LaB6–W2B5–NbB2 System

Glass Physics and Chemistry - Crystallized alloys in the LaB6–W2B5–NbB2 system are obtained by melting in an electric arc discharge and rapid cooling in an inert gas (Ar) flow. The...     

放电等离子烧结制备AlON陶瓷

以A1N粉和A12O3为原料，用放电等离子烧结(SPS)技术制备单相A1ON陶瓷。研究表明：用SPS技术在1700℃仅保温3min就可得到99TD％的A1ON陶瓷，该技术是实现A1ON陶瓷低温快速烧结的有效途径。     

Zirconium Carbide–Tungsten Cermets Prepared by In Situ Reaction Sintering

Zirconium carbide–tungsten (ZrC–W) cermets were prepared by a novel in situ reaction sintering process. Compacted stoichiometric zirconium oxide (ZrO₂) and tungsten carbide (WC) powders were heated to 2100°C, which produced cermets with 35 vol% ZrC and 65 vol% W consisting of an interpenetrating-type microstructure with a relative density of ∼95%. The cermets had an elastic modulus of 274 GPa, a fracture toughness of 8.3 MPa·m^1/2, and a flexural strength of 402 MPa. The ZrC content could be increased by adding excess ZrC or ZrO₂ and carbon to the precursors, which increased the density to >98%. The solid-state reaction between WC and ZrO₂ and W–ZrC solid solution were also studied thermodynamically and experimentally.     

ZrB2–ZrCxN1−x Eutectic Composites Produced by Melt Solidification

Ceramic eutectics are naturally occurring in‐situ composites and can offer superior mechanical properties. Here, ZrB₂–ZrC_xN_1?x quasi‐binary ceramic eutectic composites were produced by arc‐melting a mixture of ZrB₂, ZrC, and ZrN powders in an N₂ atmosphere. The arc‐melted ZrB₂–ZrC_xN_1?x composites containing 50 mol% of ZrB₂ (irrespective of the ZrC/ZrN ratio) showed rod‐like eutectic structures, where ZrC_xN_1?x single‐crystalline rods were dispersed in the ZrB₂ single‐crystalline matrices. Multiple orientation relationships between the ZrC_xN_1?x rods and the ZrB₂ matrices were observed, and one was determined as ZrB₂ {} //Zr_xN_1?x {111} and ZrB₂ < > //ZrC_xN_1?x < > . The rod‐like eutectic composites had higher hardness than the hypo‐ and hypereutectic composites and the 50ZrB₂–40ZrC–10ZrN (mol%) eutectic composite showed the highest Vickers hardness (H_v) of 19 GPa.     

放电等离子烧结工艺制备Ti2AlC材料的研究

以元素粉钛、铝、碳为原料，采用放电等离子烧结工艺在1100℃的温度下成功地制备了高纯、致密Ti2AlC材料。合成材料的x-射线衍射(XRD)和扫描电镜(SEM)分析的结果表明：多晶体Ti2AlC形貌为板状结晶，晶粒大小平约为20μm，厚度在3—5μm。     

无压烧结制备Al2O3/SiC纳米复合陶瓷

用沉淀法包裹微米级SiC颗粒，通过常压、埋烧制备Al2O3／SiC纳米复合陶瓷。通过XRD、TG和SEM等分析了煅烧和烧结过程中相组成的变化、烧成收缩和显微结构。结果表明：利用SiC粉埋烧及碳粉制造还原气氛，含8wt％SiC(平均粒径为5mm)的复合粉末经800℃煅烧、成型，试样于1550℃，2h烧结，可制备Al2O3／SiC纳米复合陶瓷，其相对体积密度达95．2％，在烧结过程中由SiC氧化形成的无定形SiO2及与基质氧化铝反应形成的莫来石前躯体可大大促进烧结。     

Porous YbB6 Ceramics Prepared by In Situ Reaction between Yb2O3 and B4C Combined with Partial Sintering

Porous YbB₆ ceramic, a member of the ultrahigh‐temperature (UHT) family, is successfully prepared from Yb₂O₃ and B₄C powders by in situ synthesis combined with partial sintering method. Due to the fact that pores can be produced using the gases such as B₂O₃ and CO generated in reaction between Yb₂O₃ and B₄C, phase‐pure porous YbB₆ ceramics are obtained after sintering the Yb₂O₃/B₄C green bodies at 1750°C for 2 h in a flowing argon atmosphere under ambient pressure without addition of pore‐forming agent. Using this new and simple method, the porosity and volume shrinkage of porous YbB₆ ceramics are controllable by changing the green density. The prepared porous YbB₆ ceramic has homogeneous pore structure with very narrow pore diameter distribution. Furthermore, the porous YbB₆ possesses high compressive strength of ~21.34 MPa when the porosity is ~58.7% and the density is ~2.27 g/cm³. The combination of these favorable properties renders porous YbB₆ ceramic being a light‐weight structural and functional component for UHT applications.     

NaB5C–B5/C Composite Ceramics Prepared by Reaction Sintering in Na Vapor

Reaction sintering of sodium carbaboride (NaB₅C) was performed by heating compacts of mixtures of amorphous boron (B) and carbon black (C) powders (B/C molar ratio, 5/1) at 1173 K in Na vapor. The ceramics obtained from the compacts of B₅/C powder mixed with a ball mill (compact density, 1.67 Mg/m³) were the composites of NaB₅C (74 mass%) and unreacted B₅/C (26 mass%). The bulk density and bending strength of the composite ceramics were 2.04 ± 0.03 Mg/m³ and 320.9 ± 10.4 MPa, respectively. Transmission electron microscope observation revealed that nanometer‐size amorphous grains of B or C were included in the matrix of NaB₅C.     

放电等离子烧结氮化铝透明陶瓷

利用放电等离子烧结(spark plasma sintering,SPS)技术开展对氮化铝透明陶瓷的研究.分析了原料粉的特性,烧结工艺对烧结体的影响以及所制备的氮化铝透明陶瓷的显微结构.     

Microstructure and mechanical properties of B4C–TiB2–SiC composites toughened by composite structural toughening phases

B₄C–TiB₂–SiC composites toughened by composite structural toughening phases, which are the units of (TiB₂–SiC) composite, were fabricated through reactive hot pressing with B₄C, TiC, and Si as raw materials. The units of (TiB₂–SiC) composite with the size of 10‐20 μm are composed of interlocking TiB₂ and SiC with the size of 1‐5 μm. The addition of TiC and Si can effectively promote the sintering of B₄C ceramics. The relative densities of all the B₄C composites with different contents of TiB₂ and SiC are close to completely dense (98.9%‐99.4%), thereby resulting in superior hardness (33.1‐36.2 GPa). With the increase in the content of TiB₂ and SiC, the already improved fracture toughness of the B₄C composite continuously increases (5.3‐6.5 MPa·m^1/2), but the flexure strength initially increases and then decreases. When cracks cross the units of the (TiB₂–SiC) composite, the cracks deflect along the interior boundary of TiB₂ and SiC inside the units. As the crack growth path is lengthened, the crack propagation direction is changed, thereby consuming more crack extension energy. The cumulative contributions improve the fracture toughness of the B₄C composite. Therefore, the composite structural toughening units of the (TiB₂–SiC) composite play an important role in reinforcing the fracture toughness of the composites.     

Novel Crystal Growth of In Situ WC in Selective Laser‐Melted W–C–Ni Ternary System

The bulk‐form in situ WC‐based cermets were prepared by selective laser melting of W–C–Ni ternary powder system. The in situ formed WC crystals generally had a unique triangular microstructure which was developed via a layer‐by‐layer growth mechanism by the multilayered stacking of (0001) basal planes of WC. An increase in the applied laser energy density, which was realized by increasing laser power or decreasing scan speed, resulted in the coarsening of in situ WC crystals in both side length and thickness, due to the elevated heat accumulation at the tips of the triangular WC crystals.     

Si3N4/Al反应烧结制备AlN/Al复合材料

研究了采用Si3N4与Al的混合粉,经压制、烧结制备AlN/Al-Si复合材料的技术方法.试验结果表明:AlN的反应生成机制属于一种连续渐进式反应形成过程,即于高温下液相Al中的Al原子渗入Si3N4的晶体点阵取代Si原子而逐渐使之向AlN晶体点阵转化的过程.被取代的Si原子从固相Si3N4中析出,扩散溶入液相Al中,冷却后形成Al-Si合金固溶体,一般呈网状分布于AlN晶体相的周围.新生成的AlN与Al-Si合金相之间表现出很好的界面亲和性.