高熵(Zr,Hf,Nb,Ta)C微米长方体的制备、吸波性能和抗氧化性研究

针对高熵碳化物制备困难,本文采用ZrC、HfC、NbC和TaC粉为原料,Ni粉为熔剂,通过低温无压烧结工艺成功制备出三种不同成分的高熵(Zr, Hf, Nb, Ta)C粉体。结果表明,三种粉体均为微米长方体,且暴露(100)晶面。(Zr_1/4Hf_1/4Nb_1/4Ta_1/4)C微米长方体因具有高介电常数而展现出优异的吸波性能,在厚度为3.5 mm、频率为6.16 GHz时,最低反射损耗值可达-48.86 dB。高熵(Zr, Hf, Nb, Ta)C微米长方体在800～1 200℃下展示出优异的抗氧化性,且氧化产物均由正交相(Nb_xTa_1-x)₂O₅固溶体、单斜相(Zr_xHf_1-x)O₂固溶体和正交相HfO₂所组成,与氧化温度和过渡金属的物质的量比无关。Zr、Hf、Nb和Ta的协同作用导致其氧化机制与单组元碳化物截然不同,Hf的存...     

(Ti1/6V1/6Nb1/6Ta1/6Mo1/3)C高熵陶瓷的制备、微观结构与抗磨损性能

过渡金属碳化物陶瓷是超高温陶瓷的典型代表,具有极高的熔点和硬度,而韧性和耐磨性有待提高。近年来,在高熵理论指导下合成的多元碳化物固溶体—高熵碳化物陶瓷具有更高的熔点和良好的韧性。本工作采用放电等离子烧结(SPS)制备了具有优异耐磨性能的(Ti_1/6V_1/6Nb_1/6Ta_1/6Mo_1/3)C 高熵陶瓷。研究了 1 600～2 100 ℃烧结的(Ti_1/6V_1/6Nb_1/6Ta_1/6Mo_1/3)C 高熵陶瓷的致密化行为、物相、微观形貌、力学和耐磨性能。结果表明,烧结温度为 1 700 ℃时,可得到面心立方结构的(Ti_1/6V_1/6Nb_1/6Ta_1/6Mo_1/3)C 高熵陶瓷。1 900 ℃以上时,高熵陶瓷相对密度大于 98%。烧结温度由 1 700 ℃升高至 2 1...     

Ti(C,N)基金属陶瓷氧化后的显微结构与力学性能

研究了Ti(C,N)基金属陶瓷的高温抗氧化性能。采用X R D、SEM分析了样品氧化后的物相组成及显微结构,并测试了试样氧化前后的抗弯强度和维氏硬度。实验结果表明:Ti(C,N)基金属陶瓷在800℃时氧化不明显,但抗弯强度开始下降;样品在900℃时开始剧烈氧化,材料的抗弯强度呈现明显的下降趋势,试样氧化前后的硬度变化较小。随着氧化温度的升高,氧化层厚度明显增加,Ti(C,N)被氧化变成TiO 2。     

高熵(TiVTaMoW)C陶瓷与不同配副间的摩擦磨损特性

为探究高熵碳化物陶瓷作为耐磨部件在摩擦学领域中的应用前景,以金属碳化物为原料,通过高能球磨和两步热压烧结法制备了一种元素分布均匀、无偏聚和偏析的高熵(Ti VTaMoW)C 陶瓷。研究了(Ti VTaMoW)C 与 Al₂O₃、Si C 和 Si₃N₄3 种配副材料在室温及 800 ℃条件下的摩擦磨损特性。结果表明：室温条件下,(Ti VTa Mo W)C 与 3 种配副对摩均表现出优异的摩擦学性能,尤其与 Si C 对摩具有最低的摩擦系数和磨损率,分别可低至(0.38±0.01)和(1.52±0.36)×10^–7 mm³/(N·m)。800 ℃条件下,(Ti VTa Mo W)C 表面氧化严重,磨损明显加剧,磨损率上升至 10^–4 mm³/(N·m)数量级。高温氧化生成的 Mo O₃和 V₂O₅具有较低剪切强度,摩擦过程转移至配副球接触面上形成转...     

原位生成陶瓷相结合Ti(C,N)复合材料及其性能研究

以TiO₂粉、鳞片石墨和Si粉为原料,采用碳热还原氮化法在1 450℃保温2 h制备了陶瓷相结合Ti(C,N)复合材料。研究了Si粉加入量(加入质量分数分别为0、5%、15%、25%)对材料物相组成、显微结构、物理性能及抗氧化性的影响。结果表明：适量Si粉的引入有利于细化Ti(C,N)晶粒,提高Ti(C,N)复合材料的常温力学性能与抗氧化性。当Si粉加入量为5%(w)时,原位生成陶瓷相结合Ti(C,N)复合材料的综合性能较优,其显气孔率、常温抗折强度和常温弹性模量分别约为(38.8±1.6)%、(62.5±2.4)MPa及(59.6±2.2)GPa。随Si粉加入量(w)进一步增加至15%或25%,复合材料的体积密度和力学性能下降。     

(Ti,Zr,Hf)B2粉体的制备及B4C含量对中熵陶瓷高温弯曲强度的影响

高熵陶瓷是陶瓷领域近几年的研究热点,过渡金属硼化物中熵、高熵陶瓷以其优异的性能、化学反应惰性和极高的熔点,成为耐极端环境的重要候选材料。本工作首次研究了B₄C过量含量对中熵硼化物粉体合成、陶瓷致密化、微结构演变和高温弯曲强度的影响,确定了低氧含量、高烧结活性(Ti,Zr,Hf)B₂粉体的制备工艺。采用热压烧结工艺在1800℃制备的(Ti,Zr,Hf)B₂中熵陶瓷致密度高达99%以上。B₄C过量15wt%的(Ti,Zr,Hf)B₂陶瓷晶粒尺寸为5.0±2.1μm,随着B₄C过量含量增加到25wt%,晶粒尺寸明显细化至2.4±0.7μm。过量的B₄C一部分与球磨引入的Si₃N₄原位反应生成BN相,另一部分B₄C以第二相形式存在,BN和B₄C相的引入可以有效抑制中熵陶瓷烧结过程中的晶粒生长,同时也提升了材料的高温弯曲强度。B₄C过量...     

碳热还原氮化攀钢高钛高炉渣制取Ti(C,N)的研究

以攀钢高炉渣(粒度≤0.074mm,w(TiO2)=21.19%)和炭黑(w(C)=98%)为原料,在密封管式炉中通入流量0.5L·min-1的工业N2(纯度>95%),分别在1300℃、1350℃、1400℃、1450℃、1500℃保温2h以及在1450℃下分别保温0、2h、4h、6h、8h的条件下,采用碳热还原氮化法制备了Ti(C,N)。用X射线衍射仪、电子探针、图像分析仪等研究了碳氮化处理温度及保温时间对Ti(C,N)的形成及其晶粒大小的影响。结果表明碳氮化处理温度对高炉渣中Ti(C,N)的形成过程产生显著影响,温度从1300℃升至1500℃时,产物中Ti(C,N)的相对含量增大,其晶粒也逐渐长大,但超过1450℃后,影响又不太显著;在1450℃下延长保温时间能促进Ti(C,N)的生成与晶粒长大,但保温时间超过2h后,此促进作用又不太明显。     

pH值对溶胶-凝胶法制备Ba (Ti0.86Zr0.14)O3基粉体及陶瓷的影响研究

通过溶胶-凝胶一步法制备了晶粒尺寸在10 μm以下的致密的Ba (Ti0.86Zr0.14)o3基Y5V型陶瓷,系统研究了溶胶的pH值对粉体的粒径、陶瓷的烧结及介电性能的影响规律.结果 表明,溶剂的pH值对粉体的形成、粒度分布和团聚产生影响,进而影响到陶瓷的性能.pH=2.5时制备的陶瓷的最大介电常数达到21 200....     

掺杂W~(6+)的Zr(WV)_xO_y质复相陶瓷的制备及特性研究

以WO3、V2O5及ZrO2粉末为原料,用氧化物煅烧法制备了掺杂W6+的Zr(WV)xOy质复相陶瓷。结果表明,复相陶瓷纯度高,杂质含量少;采取W元素和V元素的不同配比的两种配方分别实现了W元素的少量掺杂和以W元素为主、ZrV2O7为辅的良好复合;复相陶瓷在室温到100℃呈现正热膨胀特性,继续升高温度到420℃,材料表现出负热膨胀特性。但平均线膨胀系数与纯ZrV2O7的线膨胀系数相比有明显的增大。     

(Ba0.85Ca0.15)(Ti0.90Zr0.06Sn0.04)O3-Fe2O3无铅压电陶瓷的性能研究

采用固相法制备了(Ba0.85Ca0.15) (Ti0.90Zr0.06Sn0.04)O3-xmol％Fe2O3(简写为BCTZS-xFe)无铅压电陶瓷.研究了不同掺杂量对该陶瓷的显微结构、介电、铁电及压电性能的影响.结果表明,所有样品均具有单一的钙钛矿结构,少量掺杂能使晶粒长大,提高电性能.在x=0.025时,具有最佳的综合电性能,压电常数d33 =515 pC/N,机电耦合系数kp=48.2％,机械品质因数Qm =182,2Pr=18.2 μC/cm2,2Ec =4.3 kV/cm,介电常数εr=5175.     

Low-temperature sintered (Ti,Zr, Nb,Ta, Mo)C-based composites toughened with damage-free SiCw

The high sintering temperature would have a great tendency to damage the morphology and thus properties of the silicon carbide whisker (SiC_w) in high entropy carbide-silicon carbide whisker (HEC-SiC_w) composites, which, in turn, would impact the effectiveness of the operative toughening mechanisms. The objective of this study was to achieve full contributions to the toughening effects of SiC_w by preparing (Ti, Zr, Nb, Ta, Mo)C-SiC_w composites at low temperature (1600 ℃) using cobalt as additives. Results showed that the fracture toughness of the (Ti, Zr, Nb, Ta, Mo)C bulk reinforced with 20 vol% SiC_w and 5 vol% Co was 7.2 MPa?m^1/2, which was much higher than that of the (Ti, Zr, Nb, Ta, Mo)C bulk only sintered with 5 vol% Co (3.4 MPa?m^1/2). Meanwhile, it was also higher than that of the reported HEC-20 vol% SiC_w composite sintered at 2000 ℃ (4.3 MPa?m^1/2). For the fracture toughness of HEC-SiC_w composites, it was significantly increased by the introduction of damage-free SiC_w.     

Spark plasma sintering of ZrB2- and HfB2-based Ultra High Temperature Ceramics prepared by SHS

The combination of the SHS technique and the Spark Plasma Sintering (SPS) technology was adopted in this work for the fabrication of fully dense MB₂-SiC and MB₂-MC-SiC (M = Zr, Hf) Ultra High Temperature Ceramics (UHTCs). Specifically, Zr or Hf, B₄C, Si, and (for the cases of ternary systems) graphite powders were first reacted by SHS to successfully form the desired composites. The resulting powders were then subjected to consolidation by SPS. In particular, by setting a dwell temperature level of 1800°C, a mechanical pressure of 20 MPa, and a non-isothermal heating time of 10 min, products with relative densities ≥98.5% were obtained for the all systems investigated within 30 min of total processing time. The characteristics of the resulting dense UHTCs, i.e. hardness, fracture toughness, and oxidation resistance, are similar to, and in some cases superior than, those related to analogous products synthesized by alternative, less rapid, methods. The article is published in the original.     

(Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy ceramics with low thermal conductivity

A novel high‐entropy carbide ceramic, (Hf_0.2Zr_0.2Ta_0.2Nb_0.2Ti_0.2)C, with a single‐phase rock salt structure, was synthesized by spark plasma sintering. X‐ray diffraction confirmed the formation of a single‐phase rock salt structure at 26‐1140°C in Argon atmosphere, in which the 5 metal elements may share a cation position while the C element occupies the anion position. (Hf_0.2Zr_0.2Ta_0.2Nb_0.2Ti_0.2)C exhibits a much lower thermal diffusivity and conductivity than the binary carbides HfC, ZrC, TaC, and TiC, which may result from the significant phonon scattering at its distorted anion sublattice. (Hf_0.2Zr_0.2Ta_0.2Nb_0.2Ti_0.2)C inherits the high elastic modulus and hardness of the binary carbide ceramics.     

低温合成Ti3SiC2陶瓷

采用机械合金化和放电等离子烧结技术制备了纯度较高的Ti3SiC2陶瓷,研究了微量Al对Ti3SiC2的机械合金化和放电等离子烧结过程的影响.结果表明:添加适量的Al可以显著提高机械合金化及放电等离子烧结产物中Ti3SiC2的含量,并显著降低高纯度Ti3SiC2的烧结温度.机械合金化10h,成分为3Ti/Si/2C/0.2Al(摩尔比)的混合粉体,经850℃放电等离子烧结可获得质量分数(下同)高达96%的Ti3SiC2块体,烧结温度提高到1 100℃,可获得纯度为99.3%、相对密度高达98.9%的Ti3SiC2致密块体.     

Spark plasma sintering of SiAlON ceramics

Investigated was the spark plasma sintering (SPS) of sialon ceramics from SHS-produced powders. Experimentally established were (a) sintering temperatures that ensure a required density, phase composition, and microstructure of sintered multicomponent sialon ceramics, (b) individual stages of the SPS process, and (c) the effect of starting powder composition on the phase composition and microstructure of sintered sialon ceramics.