Influence of powder characteristics on gas pressure sintering of Si3N4

The sintering behaviours of four kinds of Si₃N₄ powders were investigated by dilatometry in 10 atm N₂ at 1890, 1930 and 2050° C. The sinterabilities of powders were compared and discussed in relation to the powder characteristics. A large size distribution in the powder accelerated grain and pore growth at <1800° C, which resulted in the inhibition of further densification at >1800° C. The presence of carbon in a powder prevented densification. A powder with a uniform grain size kept the microstructure of the sintered material uniform during sintering at <1800° C and gave a high degree of shrinkage at >1800° C. Densification at >1800° C was accompanied by the dissolution of equi-axial -Si₃N₄ grains and reprecipitation as elongated -Si₃N₄ grains from the oxynitride liquid. The relation between the densification and microstructure is discussed in terms of the relative rates of densification and grain growth.     

Influence of N<Subscript>2</Subscript> partial pressure on the microstructure,hardness, and thermal stability of CrZrSiN nanocomposite coatings

The effects of N₂ partial pressure in the unbalanced magnetron sputtering process on the microstructure, hardness, and thermal stability of the CrZrSiN nanocomposite coating were investigated. A typical nanocomposite structure, composed of a crystalline phase and an amorphous phase was obtained and the distribution of these phases changed with increasing N₂ partial pressure. The N_1s spectra revealed the presence of two-peak characteristic of nitrogen in the CrZrN and SiN _x phases, and the ratio of the peak’s SiN _x to CrZrN intensity increased with increasing N₂ partial pressure, indicating an increase in the amorphous phase in the nanocomposite microstructure. As N₂ partial pressure increased, the CrZrSiN coating hardness decreased from 38 to 30 GPa due to the increasing amount of the SiN _x amorphous phase. After the thermal stability test, the hardness values of the CrZrSiN coatings were maintained at approximately 30 GPa up to 800°C, but the hardness decreased rapidly to 18 GPa after annealing at 900°C. This drastic change of hardness over 900C was due to the formation of a Cr₂O₃ phase in the CrZrSiN coating.     

Influence of a positive pressure gradient on the characteristics of a turbulent boundary layer

Based on a systematic analysis of present day experimental data published in the literature, a modified Prandtl—Clauser turbulence model is presented which makes it possible to take into account the effect of a positive pressure gradient on the average characteristics of a turbulent boundary layer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 2, pp. 232–239, August, 1988.     

Characterization of TiCr(C,N)/amorphous carbon coatings synthesized by a cathodic arc deposition process

Ternary TiCrN and nanocomposite TiCr(C,N)/amorphous carbon (a-C) coatings with different carbon contents (0-26.6 at.%) were synthesized by cathodic arc evaporation with plasma enhanced duct equipment. The structural, chemical, and mechanical properties of the deposited films were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and nanoindentation measurement. The atomic content ratios of carbon/(Ti + Cr) and carbon/nitrogen increased with increasing C₂H₂ flow rate. A nanocomposite structure of coexisting metastable hard TiCr(C,N) crystallites and amorphous carbon phases was found in the TiCr(C,N)/a-C coatings, those possessed smaller crystallite sizes than the ternary TiCrN film. XPS analyses revealed the concentration of a-C increased with increasing carbon content from 8.9 at.% to 26.6 at.%. Exceeding the metastable solubility range of carbon within the TiCrN lattice, the carbon formed a-C phase in the deposited coatings. The nanocomposite TiCr(C,N)/a-C coatings exhibited higher hardness value of 29-31 GPa than the deposited TiCrN coating (26 ± 1 GPa). It has been found that the structural and mechanical properties of the films were correlated with the carbon content in the TiCr(C,N)/a-C coatings.     

Influence of N2 partial pressure on mechanical properties of (Ti,Al)N films deposited by reactive magnetron sputtering

The influence of the nitrogen partial pressure on the mechanical properties of (Ti,Al)N films deposited by DC reactive magnetron sputtering using a Ti-Al mosaic target at a substrate bias of −100 V is investigated. Nanoindentation tests reveal that with increasing N₂ partial pressure, the film hardness and elastic modulus increase initially and then decrease afterwards. The maximum hardness and elastic modulus are 43.4 GPa and 430.8 GPa, respectively. The trend is believed to stem from the variations in the grain size and preferential orientation of the crystals in the (Ti,Al)N films fabricated at varying N₂ partial pressure. The phenomenon is confirmed by results acquired using glancing angle X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS).     

Influence of oxygen partial pressure on the wetting of SiC by a Co–Si alloy

In this investigation the influence of oxygen partial pressure P_O2 on the wetting of SiC by a Co–Si alloy was studied. Wetting experiments were carried out in argon with different oxygen contents (from 5 to 1000 ppm). The relationship between wetting and deoxidation of surfaces (SiC and Co–Si alloy) was investigated. Calculations were performed to evaluate the temperature range over which deoxidation is possible. These calculations are in agreement with the experimental results.     

氧分压对RF磁控溅射ZrO2薄膜生长特性的影响

采用反应射频(RF)磁控溅射法在n型(100)单晶S基片上沉积了ZrO2膜,研究了氧分压与ZrO：薄膜的表面粗糙度和沉积速率、SiO2中间界层的厚度以及ZrO2薄膜的折射率之间关系。结果表明：随着氧分压增高,薄膜的沉积速率降低,表面粗糙度线性地增加;在低的氧分压情况下,Si基片表面的本征SiO2层的厚度增加幅度较小,在高的氧分压情况下,Si基片表面的本征SiO2层的厚度有较大幅度地增加;在O2／Ar混和气氛下,溅射沉积的ZrO2薄膜的折射率受氧分压的影响不显著,而在纯氧气气氛环境下,ZrO2薄膜的折射率明显偏低,薄膜的致密性变差。     

C形纵剖面部分球冠换能器结构对声焦域的影响

在球带腔形聚焦超声换能器的基础上,设计一种C形纵剖面部分球冠聚焦超声换能器,研究其结构参数变化对声焦域形态的影响。通过建立的有限元仿真模型,分别讨论了换能器的球带高度和聚焦夹角与焦域形态的变化关系。结果表明,球带高度越高、聚焦夹角越大,其焦域尺寸越小,焦域长轴与短轴的比值越低,焦域趋近于圆形,尤其是当球带高度为1.6F（F为焦距）、聚焦夹角≥210°时,其焦域三轴尺寸均可达到亚波长尺度。为验证仿真结果的正确性,设计制作了一个可改变聚焦夹角的换能器并进行了测试,实验与仿真结果大致相符。设计的换能器相对于传统行波换能器,焦域形态得到了明显改善,能够压缩焦域长短轴之比,有效提高聚焦精度,为改善聚焦超声换能器焦域形态提供了一种设计方法。     

Influence of Ti coatings on field emission characteristics of nano-sheet carbon films

Nano-sheet carbon films (NSCFs) coated with a 2-nm Ti layer were fabricated on n-type Si (110) by means of a quartz-tube-type microwave-plasma chemical-vapour-deposition (MWPCVD) method with hydrogen-methane gas mixture and an electron beam (EB) evaporation method. The field emission (FE) properties of the NSCF were changed by depositing a thin Ti film on its surface. The threshold field was decreased from 3.7 V/μm to 2.5 V/μm and the FE current density at a macroscopic electric field (E) of 10 V/μm was decreased from 41.7 mA/cm² to 26.3 mA/cm² for Ti-coated NSCFs. Moreover, the saturation tendency of the emission current density was not improved for Ti-coated NSCFs. A three-region E model considering statistical size effects of FE tip structures in the low E region and space-charge-limited-current (SCLC) effects in the high E region was proposed and the FE data in the low, middle and high E regions were reasonably interpreted.     

射频反应溅射中N2分量对TiN薄膜性质的影响

用射频反应溅射的方法制备了TiN薄膜，其晶体结构与电阻率都与溅射气氛中N2分量有直接关系。随着N2分量由5％增加到50％，薄膜先是呈现（111）的择优取向，后是呈现（200）的取向，最后没有衍射峰出现，结构趋于无定型，于此同时，电阻率也由接近金属的良好导电性变为半导体的导电性。     

溅射气压对ZrO2薄膜微结构与光学性能的影响

利用射频反应磁控溅射在显微玻璃、单晶硅片、NaCl和石英上沉积ZrO2薄膜.膜厚60～80nm.研究发现,溅射气压升高,薄膜结晶程度降低,同时存在单斜相和四方相;晶粒尺寸增大;折射率上升;透射率在700～1000nm波段上升.这些结果表明溅射气压影响ZrO2薄膜生长机制、微观结构和成份,进而影响其光学性能.     

氧分压对Al2O3:Ce薄膜的发光性能及表面形貌的影响

应用中频反应磁控溅射设备制备了Al2O3:Ce3+的非晶薄膜。在溅射时靶电压随氧气分压比的增加而减小,而当氧分压比增大时靶电压沿另一条路径变化,即呈现迟滞回线现象。通过控制氧分压比改变Al2O3:Ce3+薄膜的发光性质。经光致发光检测,薄膜的光致发光谱是在374nm附近的非对称波峰,它来自于Ce3+离子的5d1激发态向基态4f1的两个劈裂能级的跃迁。Ce3+含量和薄膜的化学成分是通过X射线散射能谱(EDS)测量的。当氧分压比增加时薄膜的发光强度增加,在氧分压比为15%是发光强度最大,其后随氧分压比增大发光强度有减小趋势。薄膜的厚度随氧分压比的增加而呈减小的趋势。X射线衍射(XRD)检测表明所制备透明薄膜为非晶态。扫描电镜检测(SEM)显示,随着氧分压的增加非晶薄膜表面趋于致密平滑。发射纯蓝光的Al2O3:Ce3+非晶薄膜在平板显示等领域有着广泛的潜在应用前景。     

分层对TC4钛合金板抗平头弹撞击失效特性的影响

使用Abaqus/Explicit有限元分析软件,开展平头弹撞击不同厚度双层TC4钛合金板数值模拟,研究双层TC4钛合金板撞击失效特性与失效模式随厚度变化规律及机理.通过对比撞击试验与仿真结果,验证数值模型和参数的有效性.在此基础上与等厚度单层TC4钛合金板的抗侵彻性能进行对比,结果表明,对于12.68 mm直径的平头...     

水热法制备MnO2的电容特性

采用水热法制备了超级电容器MnO2电极材料,以单因素实验确定了最佳的制备条件为:水热处理温度为120℃和反应时间为6h.XRD测试结果表明,所制得的MnO2是α-MnO2和r-MnO2的混合晶型.最佳制备条件下所制得的MnO2的比电容达168.39 F·g-1.为改善MnO2的倍率特性进行Al掺杂,XRD的测试结果表明,Al3 进入到MnO2的晶格中.电化学测试结果表明,掺Al改善了电极材料的倍率特性和循环稳定性.     

Influence of target geometry on the parameters of a laser-emission discharge

The relationship between the geometry of a plasma-forming target and the parameters of a laser-emission discharge is investigated. It is shown that by selecting the corresponding geometry of an irradiated sample it is possible to change the coefficient of laser radiation energy conversion into the energy of unidirectional quasistationary electric current. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 240–242, March–April, 2008.