新型Si3N4/TiCnano复合陶瓷材料的制备及性能

本文利用热压烧结方式制备了新型Si3N4/TiCnano复合陶瓷材料,对材料的配方及烧结工艺进行了优化,采用XRD、SEM等手段分析了材料的微观结构,研究了烧结条件对材料性能的影响机理。结果表明,所研究的材料具有良好的力学性能。     

Densification,microstructure, and mechanical properties of ZrC–SiC ceramics

ZrC–SiC ceramics were fabricated by high-energy ball milling and reactive hot pressing of ZrH₂, carbon black, and varying amounts of SiC. The ceramics were composed of nominally pure ZrC containing 0 to 30 vol% SiC particles. The relative density increased as SiC content increased, from 96.8% for nominally pure ZrC to 99.3% for ZrC-30 vol% SiC. As SiC content increased from 0 to 30 vol%, Young's modulus increased from 404 ± 11 to 420 ± 9 GPa and Vickers hardness increased from 18.5 ± 0.7 to 23.0 ± 0.5 GPa due to a combination of the higher relative density of ceramics with higher SiC content and the higher Young's modulus and hardness of SiC compared to ZrC. Flexure strength was 308 ± 11 MPa for pure ZrC, but increased to 576 ± 49 MPa for a SiC content of 30 vol%. Fracture toughness was 2.3 ± 0.2 MPa·m^1/2 for pure ZrC and increased to about 3.0 ± 0.1 MPa·m^1/2 for compositions containing SiC additions. The combination of high-energy ball milling and reactive hot pressing was able to produce ZrC–SiC ceramics with sub-micron grain sizes and high relative densities with higher strengths than previously reported for similar materials.     

High-strength medium-entropy (Ti,Zr,Hf)C ceramics up to 1800°C

Medium-entropy (Ti,Zr,Hf)C ceramics were prepared by hot pressing a dual-phase medium-entropy carbide powder with low oxygen content (0.45 wt%). The results demonstrate that the medium-entropy (Ti,Zr,Hf)C ceramics sintered at 2100°C had a relative density of 99.2% and an average grain size of 1.9 ± 0.6 μm. The flexural strength of (Ti,Zr,Hf)C carbide ceramics at room temperature was 579 ± 62 MPa. With an increase in temperature to 1600°C, the flexural strength showed an increase up to 619 ± 57 MPa, and had no significant degradation even up to 1800°C. The high-temperature flexural strengths of (Ti,Zr,Hf)C were obviously higher than those of the monocarbide ceramics (TiC, ZrC, and HfC). The primary strengthening mechanism in (Ti,Zr,Hf)C could be attributed to the high lattice parameter mismatch effects between TiC and ZrC, which not only inhibited the fast grain coarsening of (Ti,Zr,Hf)C ceramics, but also increased the grain-boundary strength of the obtained ceramics.     

Microstructure and mechanical properties of TaC ceramics with 1–7.5 mol% Si as sintering aid

Metallic Si as sintering aid was effective in densifying tantalum carbide ceramic (TaC) by spark plasma sintering (SPS) at 1700°C. Full density was reached at 5.0 mol% Si addition (equivalent to 1.088% Si in weight) and above. Enhanced densification of TaC ceramic with Si was associated with decrease in oxygen content from ~0.24 wt% in TaC powder to ~0.03 wt% in consolidated specimen. Rest of the oxygen species was collected at multigrain conjunctions to form SiO₂‐based liquid at high temperatures. Upon cooling, Ta, Si, O, and C dissolving in the liquid precipitated minor phases of TaSi_x and SiC of low concentrations. Microstructure of TaC ceramics was refined by the Si addition, with average grain size decreasing from 11±8 μm at 1.0 mol% Si to 3±2 μm at 7.5 mol% Si addition. Ta solute in SiC and Si solute in TaC were evidenced. TaC ceramic containing 7.5 mol% Si had a relatively good flexural strength and fracture toughness of 646±51 MPa and 5.0 MPa·m^1/2, respectively.     

TiO_2含量对微波介质瓷Zr_xTi_(1-x)O_2致密化、微结构及介电性能的影响

制备了一系列ZrxTi1-xO2(x =0.40~0.60)微波介质瓷,对其致密化、微结构及介电性能进行了研究. XRD物相分析样品为单一均相的ZrTiO4. 在相同的烧结温度下,TiO2含量越高,样品越不易致密,相对密度越低,晶粒越易长大. 样品的相对密度越高,其介电常数和品质因数越大. 相对密度高于90%时,对样品介电性能的影响可以忽略,成份起主导作用. 随着TiO2含量增加,样品的介电常数增大,品质因数降低.     

Strength of single-phase high-entropy carbide ceramics up to 2300°C

The mechanical properties of single-phase (Hf,Zr,Ti,Ta,Nb)C high-entropy carbide (HEC) ceramics were investigated. Ceramics with relative density >99% and an average grain size of 0.9 ± 0.3 µm were produced by a two-step process that involved carbothermal reduction at 1600°C and hot pressing at 1900°C. At room temperature, Vickers hardness was 25.0 ± 1.0 GPa at a load of 4.9 N, Young's modulus was 450 GPa, chevron notch fracture toughness was 3.5 ± 0.3 MPa·m^1/2, and four-point flexural strength was 421 ± 27 MPa. With increasing temperature, flexural strength stayed above ~400 MPa up to 1800°C, then decreased nearly linearly to 318 ± 21 MPa at 2000°C and to 93 ± 10 MPa at 2300°C. No significant changes in relative density or average grain size were noted after testing at elevated temperatures. The degradation of flexural strength above 1800°C was attributed to a decrease in dislocation density that was accompanied by an increase in dislocation motion. These are the first reported flexural strengths of HEC ceramics at elevated temperatures.     

ZrB_2-YAG陶瓷的烧结致密化

通过共沉淀法获得包覆式Al2O3-Y2O3/ZrB2复合粉体,对其进行放电等离子烧结以提高ZxB2陶瓷的烧结致密度.用扫描电镜观察试样的显微结构,用X射线衍射仪对试样进行物相分析.结果表明:包覆犁粉体在700～1 000℃时出现1次大的收缩,然后出现1个不收缩的平台,当温度达到1 100℃之后出现第2次收缩.适宜制备高致密的ZrB2-钇铝石榴石(yttrium aluminium garnet,YAG)陶瓷的工艺条件为;烧结温度为1 700℃,烧结压力为20MPa,保温时间为4min,YAG的添加量为30%(质量分数),所制备的ZrB2-YAG陶瓷相对密度大于95%.     

提高钻井泵陶瓷缸套使用寿命的研究

高压泥浆泵是油田钻井工作台的＂心脏＂,而缸套是泥浆泵的重要磨损部件。工程陶瓷以其高硬度、高耐磨性,耐腐蚀性、表面性能好等优点,在钻井泵缸套中已得到广泛应用。但目前陶瓷缸套的使用寿命相对较短,如何提高陶瓷缸套的使用寿命,已成为陶瓷缸套研究中亟待解决的问题。本研究通过对钻井泵缸套的分析,提出了长寿命陶瓷缸套的要求,从陶瓷材料的选择,力学性能及其微观结构等方面探讨了提高陶瓷缸套使用寿命的方法,为陶瓷缸套生产企业提供改善产品质量的依据和方法。