热压烧结制备高密度ZrB2陶瓷

在烧结温度和压力为1950℃和50MPa条件下,分别对ZrB2的原始粉末、球磨粉末、加助烧剂的粉末以及既加助烧剂又进行球磨的粉末进行热压烧结实验。采用阿基米德排水法测出了ZrB2陶瓷的密度;利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、能谱(EDS)等手段对粉体和烧结产物的物相、形貌以及成分进行了表征。结果表明:球磨且加助烧剂镍的粉体烧结所得样品致密性最好,相对密度为99.375%,接近全致密;球磨细粉烧结所得样品次之,相对密度为99.09%;添加助烧剂粉末烧结所得样品相对密度为91.45%;用原始粉末烧结所得样品致密性最差,相对密度为84.7%。采用排水法所测得密度结果与扫描电镜观察所得致密性情况一致。     

低温热压制备高硬度、高韧性Si3N4–SiCw–ZrB2陶瓷

通常低温热压烧结的Si₃N₄陶瓷具有较高的硬度和较低的断裂韧性;而高温热压烧结的Si₃N₄陶瓷具有较低的硬度和较高的断裂韧性。为了获得高硬度、高韧性Si₃N₄陶瓷,添加20%SiC_w（SiC晶须,体积分数）和2.5%ZrB2,在1 500℃低温热压制备了Si₃N₄基陶瓷,开展其相组成、致密度、显微结构和力学性能研究,并与1 800℃高温热压烧结Si₃N₄进行了对比研究。结果表明：SiC_w的引入阻碍了Si₃N₄低温致密化,致密度从97.9%降低到92.9%,Vickers硬度从20.5 GPa降低到16.4 GPa,断裂韧性从2.9 MPa·m^1/2增加到3.4 MPa·m^1/2。同步引入SiC_w和ZrB₂     

ZrB2–SiC多层陶瓷的抗氧化性

用传统陶瓷的流延工艺制备ZrB2–SiC多层陶瓷。用Archimedes法测定ZrB2–SiC多层陶瓷的相对密度。用扫描电子显微镜观察其显微结构,并进行循环抗氧化性能评价。结果表明：ZrB2–SiC多层陶瓷在1 950℃烧结的致密度达到99.7%,材料的抗氧化过程主要可分为两个阶段：第一阶段低熔点相的挥发,出现质量损失;第二阶段氧化层的形成,降低进一步氧化速率。抗氧化性能较ZrB2–SiC复相陶瓷有很大提高。     

ZrB2陶瓷制备研究进展

航天航空、新兵器、新能源等高科技领域的快速发展对超高温陶瓷材料提出了迫切的需求,ZrB2陶瓷材料是最重要的超高温陶瓷材料之一。本文阐明了ZrB2陶瓷拥有优异性能的原因,综述了ZrB2陶瓷材料的制备研究进展,介绍了固相法、气相法、前体法制备ZrB2陶瓷材料的机理,对比了各种ZrB2陶瓷材料制备方法的优缺点,并指出了有机前体转化法具有可设计性好、不含杂质元素、成型可控、陶瓷转化温度低等优点。本文总结得出有机前体转化法是制备ZrB2超高温陶瓷复合材料较理想的方法,以及基于有机聚合物的ZrB2陶瓷前体是未来重要的发展方向之一。     

锆英石碳热还原制备ZrB2-ZrO2-SiC复合粉体

以锆英石、硼酸和炭黑为原料,在流通氩气气氛中于1 500℃煅烧制备ZrB₂-ZrO₂-SiC复合粉体,研究了保温时间（分别为3、6和9 h）和添加剂AlF₃添加量（质量分数分别为0、0.5%、1.0%、1.5%、2.0%和2.5%）对合成产物物相组成和显微结构的影响。结果表明：1)将锆英石在流通氩气气氛中于1 500℃碳热还原可制备ZrB₂-ZrO₂-SiC复合粉体;ZrB₂、ZrO₂呈粒状,SiC呈纤维状。2)随着保温时间的延长,ZrB₂的量逐渐增多,m-ZrO₂和SiC的量均逐渐减少,非氧化物ZrB₂、SiC、ZrC的总量逐渐增多。3)与未添加AlF₃的试样相比,添加0.5%（w）AlF₃的试样中m-ZrO₂量显著减少,ZrB₂的量显著增多,SiC的量有所减少;但随着AlF     

热压烧结制备原位复合（TiB2+TiC）/Ti3SiC2复相陶瓷

采用热压烧结法制备了原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷。采用X射线衍射、扫描电镜和透射电镜对材料的物相组成和显微结构进行了表征,研究了烧结温度对材料物相组成、烧结性能、显微结构与力学性能的影响。结果表明:烧结温度在1 350～1 500℃范围内,随着烧结温度的升高,合成反应进行逐渐完全,材料的密度、抗弯强度和断裂韧性显著提高。1 500℃烧结可得到致密的原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷,材料晶粒发育较完善,层片状Ti3SiC2、柱状TiB2与等轴状TiC晶粒清晰可见,增强相晶粒细小,晶界干净,材料的抗弯强度、断裂韧性和Vickers硬度分别达到741 MPa,10.12 MPa.m1/2和9.65 GPa。烧结温度达到1 550℃时Ti3SiC2开始发生分解,材料的密度和力学性能又显著下降。     

B4C陶瓷中原位生成TiB2及其对力学性能的强化机制

以 TiO₂为烧结助剂,采用反应烧结法在 B₄C 陶瓷中原位生成 TiB₂,制备出致密的 B₄C 陶瓷,并对其强化机制进行了分析。结果表明：随着 Ti O₂添加量的增加,B₄C 陶瓷的致密度和抗弯强度先增大后减小,断裂韧性不断增大。当 Ti O₂添加量为 5% (质量分数)、烧结温度为 1 700 ℃时,B₄C 陶瓷致密度达到 99.6%;当 TiO₂加入量为 15%时,B₄C 陶瓷的 Vickers硬度为 36.0 GPa,断裂韧性为 4.38 MPa·m^1/2,抗弯强度为 405 MPa,综合性能最优。原位生成的 TiB₂抑制了 B₄C 陶瓷晶粒长大,消除了裂纹尖端应力,使裂纹产生偏转和分叉,对 B₄C 陶瓷起到细晶强化和增韧作用。     

制备工艺对La2O3掺杂氧化镁陶瓷性能的影响

以高纯氧化镁粉体为主要原料,分别掺杂0、2%、4%、6%以及8%（w）的La₂O₃粉体,选用聚乙烯醇为结合剂,研究单轴压成型、等静压成型及不同煅烧温度（1 400、1 500以及1 600℃）对La₂O₃掺杂氧化镁陶瓷烧结性能、显微结构及抗热震性能的影响。结果表明：采用等静压成型,氧化镁粉体受到来自各方向大小一致的成型压力,并均匀地传递至各个方向,从而得到了更为致密的坯体,显著提高了氧化镁陶瓷的烧结性能。提高烧成温度,更有利于掺杂物La₂O₃与MgO形成置换型固溶体或发生晶格畸变,促进烧结,达到致密化。煅烧温度为1 600℃,La₂O₃掺杂量为4%（w）时,经等静压成型坯体最为致密,热震后裂纹细小。这是由于方镁石晶相间交界处的La₂O₃晶体改变了裂纹走向,阻挡和分散了部分能量和应力,减缓了裂纹的线性延伸。     

添加B2O3对Y掺杂BaZrO3烧结性及电导率的影响

研究了加入不同量氧化硼（B2O3）对 Y 掺杂 BaZrO3（BaY0.1Zr0.9O2.95）质子导体烧结性及电导率的影响。研究表明：加入适量 B2O3（质量分数为0.5%～0.75%）可以使 Y 掺杂 BaZrO3的烧结温度降低到 1500 ℃,保温时间缩短到 4～6h,相对密度可达 95%左右,远大于不加 B2O3试样的。与未掺入 B2O3的 Y 掺杂 BaZrO3试样相比,该体系材料的电导率没有明显降低。过量 B2O3（1.0%）的加入将使其以第二相形式存在于烧结体中,从而降低材料的电导率。     

ZrB2-SiCpl复合陶瓷的SPS烧结行为及微观结构

利用放电等离子体烧结（spark plasma sintering,SPS）技术,在烧结温度、保温时间、压力和加热速率分别为1 600℃、5 min、30 MPa和100℃/min条件下制备硼化锆（ZrB2）–15%（体积分数）碳化硅晶片（SiCpl）复合陶瓷。研究ZrB2–SiCpl复合陶瓷的烧结致密化行为、微观结构...     

Fabrication of ZrB2 ceramics by reactive hot pressing of ZrB and B

Zirconium diboride (ZrB₂) ceramics were prepared by reactive hot pressing of ZrB+B powder mixture. Formation of a transient liquid due to eutectic reaction of ZrB₂+Zr→L_eu(ZrB2+Zr) at 1661°C following peritectic decomposition of 2ZrB=ZrB₂+Zr at 1250°C during heating up of the ZrB+B mixture facilitated densification. The liquid phase was subsequently eliminated via reaction of B with Zr in the eutectic liquid L_eu(ZrB2+Zr) to result in a dense ZrB₂ ceramic. Full density was reached after reactive hot pressing at 1900°C under 30 MPa for 1 h. The ZrB₂ ceramic had a refined microstructure consisting of grains of <1.5 μm in size and relatively good Vickers hardness (21 ± 2 GPa) and flexural strength (595 ± 63 MPa).     

Zr-B2O3-Mg体系自蔓延高温合成ZrB2陶瓷粉末

采用自蔓延高温合成(self-propagating high-temperature synthesis,SHS)技术研究了Zr-B2O3-Mg体系反应原料的不同粒度和掺量对反应产物的影响规律,并制备了ZrB2陶瓷粉末。用XRD对材料的相组成进行了分析;精确的相组成由化学分析测定;燃烧温度由SHS研究装置测量;材料的显微结构由SEM观察。XRD分析和燃烧温度曲线表明：50μmZr粉和Mg过量15％(摩尔分数)的反应体系是最理想的反应体系。SEM分析表明;SHS产物晶粒粒径为2～5gm左右．而酸洗产物晶粒粒径为0．5～2μm左右。化学分析表明：酸洗产物中含有ZrB2(94．59％,质量分数,下同),ZrO2(3．87％),H3BO3(1．54％)。     

In situ hot-pressed ZrB2-based composite with polycarbosilane-derived SiC: Microstructure and mechanical behavior

In this study, a homogenously dispersed finer SiC particles-containing ZrB₂ composite was prepared using nanosized polycarbosilane (PCS) particles-containing ZrB₂ mixture powder, followed by hot pressing. The microstructure of the resulting composite was characterized by field-emission scanning electron microscopy and transmission electron microscopy. The composite microstructure comprised finer equiaxed ZrB₂ and SiC grains. The mechanical behavior of the composite was evaluated using four-point bending test at different temperatures between room temperature (RT) and 1600°C. The results show that the composite exhibited only linear deformation behavior prior fracture at or below 1500°C. However, a trace quantity of nonlinear deformation was observed at 1600°C. In addition, the flexural strength of the composite decreased as the temperature increased from RT to 1200°C, then the strength increased as the temperature raised to 1400°C. Subsequently, the flexural strength remained almost the constant between 1400°C and 1600°C, with a strength of ~760 MPa.     

Electrochemical corrosion behavior and surface modification of ZrB2 in hydrofluoric acid aqueous solution

The electrochemical corrosion behavior in an open system of zirconium diboride (ZrB₂) was studied in hydrofluoric acid aqueous solution at room temperature. Based on analysis of the intermediate products of corrosion, a corrosion mechanism for ZrB₂ is suggested. The morphology evolution of anodic ZrB₂ is investigated. The density of the hexagonal‐pyramid grain array is dictated by current density, and the time dictates the length of the hexagonal pyramid grains. The microstructure of the surface can be controlled by the current density, which demonstrates that the surface wettability of ZrB₂ can be modified by tailoring the current density.     

ZrB2-based solid solution ceramics and their mechanical and thermal properties

Zirconium diboride ceramics as one of the main members of ultrahigh-temperature ceramics are capable of being used as structural components at ultrahigh temperatures. Entropy adjusting is a newly developed approach to improving the properties of ceramics. In this work, a series of ZrB₂-based solid solution ceramics with different mixing entropies, formulated (Zr_xTi_yNb_yTa_y)B₂ (x = .25, .85, .925, .9625, 1; x + 3y = 1), were prepared by adjusting the content of other diborides. Diboride solid solution powders were synthesized by boro/carbothermal reduction process and then densified by spark plasma sintering. The results show that the formation of a single-phase solid solution is independent of the mixing entropy in (Zr_xTi_yNb_yTa_y)B₂ system. The addition of other diborides into ZrB₂ is beneficial to reduce the particle size of the synthesized powder and promote the densification process. The dense sintered samples with higher mixing entropy have finer grain size, higher hardness, and modulus. The (Zr_0.25Ti_0.25Nb_0.25Ta_0.25)B₂ ceramic has the highest hardness of 31 GPa and a modulus of 682 GPa. Severe lattice distortion in samples with higher mixing entropy will result in increased phonon scattering and lower thermal conductivity.     

Thermal properties of ZrB2-TiB2 solid solutions

Zirconium diboride ceramics were prepared with additions of up to 50 vol.% TiB₂. The resulting (Zr,Ti)B₂ ceramics formed complete solid solutions based on x-ray diffraction. The addition of TiB₂ resulted in grain size decreasing from 22 μm for nominally pure ZrB₂ to 7 μm for ZrB₂–50 vol.% TiB₂. The thermal conductivity at 25°C ranged from 93 W/m⋅K for nominally pure ZrB₂ to 58 W/m⋅K for ZrB₂–50 vol.% TiB₂. Thermal conductivity was as high as 67 W/m⋅K for nominally pure ZrB₂ at 2000°C, but dropped to 59 W/m K with the addition of 50 vol.% TiB₂. Electrical resistivity measurements were used to calculate the electron contribution to thermal conductivity, which was 76 W/m⋅K for nominally pure ZrB₂ decreasing to 57 W/m⋅K when 50 vol.% TiB₂ was added. The phonon contribution to thermal conductivity did not change significantly for ≤10 vol.% TiB₂. Additions of ≥25 vol.% TiB₂ reduced the phonon contribution to nearly zero for all temperatures.     

Pressureless Sintering and Properties of Titanium Diboride Ceramics Containing Chromium and Iron

The simultaneous addition of 0.5 wt% Cr and Fe was found to enhance the densification of TiB₂. The densities of specimens that were sintered for 2 h at 1800° and 1900°C were 97.6% and 98.8% of the theoretical value, respectively. The mechanical properties of the specimen sintered at 1800°C, which had a strength of 506 MPa and a fracture toughness of 6.16 MPa·m^1/2, were much better than those observed in the specimen sintered at 1900°C.     

ZrB2-Al2O3复合粉体的自蔓延高温还原合成与表征

用自蔓延高温还原合成制备了ZrB2-Al2O3复合粉体。用X射线衍射仪、扫描电镜和透射电镜等分析测试手段,对所制得的复合粉体的相组成、相貌及微观组织进行了表征。结果表明：ZrB2和Al2O3以主晶相的形式存在于复合粉体之中,二者存在良好的界面结合,这主要与ZrB2在Al2O3颗粒表面结晶生长有关。