爆炸焊接制备超导射频腔的铌-316L不锈钢过渡接头

Nb/316L不锈钢过渡接头的研究可以为改进超导射频腔氦夹克的材料带来新的突破。本文利用爆炸焊接方式进行了铌和316L不锈钢的连接。为了观察复合材料的性能,对爆炸焊接和热处理后的复合材料进行了结合面微观结构和力学性能研究。微观结构研究表明结合面没有脆性金属间化合物形成且复合材料热处理后没有发现结合面有元素扩散。我们还对复合材料进行了室温和低温环境下的拉伸测试、剪切测试和弯曲测试。拉伸测试结果表明液氮温度下复合材料的强度高于室温环境,同时还观察到在液氮环境下复合材料有分层现象出现。最后我们进行了Nb-316LSS过渡接头的设计、加工和真空检漏,结果表明真空漏率满足工程要求,从而验证了Nb-316LSS复合材料用于SRF超导腔体氦夹克的可行性。     

Mass transfer modeling on the separation of tantalum and niobium from dilute hydrofluoric media through a hollow fiber supported liquid membrane

The separation of a mixture of tantalum and niobium in dilute hydrofluoric media via hollow fiber supported liquid membrane (HFSLM) was examined. Quaternary ammonium salt (Aliquat336) diluted in kerosene was used as a carrier. The various effects on the transport and separation of tantalum and niobium were studied: concentration of hydrofluoric acid in the feed solution, concentration of the carrier (Aliquat336) in the membrane phase, types of stripping solutions (NaClO₄, thiourea and HCl) and their concentration. The extraction of tantalum in the membrane phase from 0.3 M hydrofluoric acid (HF) by 3% (v/v) Aliquat336 was achieved by leaving niobium in the feed solution. Quantitative recovery of tantalum was achieved by 0.2 M NaClO₄. Furthermore, a mathematical model focusing on the extraction side of the liquid membrane system was presented in order to predict the concentration of tantalum at different times. The mass transfer coefficients of the aqueous feed (k_i) and the organic membrane phase (k_m) were estimated as 1.19 × 10⁻⁵ and 1.39 × 10⁻⁷ cm/s, respectively. Therefore, the mass transfer limiting step is the diffusion of tantalum-Aliquat336 through the liquid membrane. Moreover, mass transfer modeling was performed and the validity of the developed model evaluated. Experimental data and theoretical values were found to be in good agreement when the concentration of Aliquat336 in the membrane phase was below 4% (v/v).     

三维原子探针对铌微合金化钢碳氮化物的析出研究

利用三维原子探针（3DAP）可以对不同元素的原子逐个进行分析,并给出纳米空间中不同元素原子的三维分布图形,分辨率接近原子尺度的优越性能,对含铌轿车横梁钢中的碳氮化物进行分析,结果表明,铌微合金化钢中存在尺寸为几个纳米大小的铌碳氮化物析出物,析出物呈薄片状,同时,铌碳氮化物在铁索体中析出是随机的。     

控制高强度含铌连铸板坯表面横裂的生产实践

表面横裂是高强度含铌连铸板坯较常见的表面缺陷之一,是导致铸坯轧后钢板表面出现结疤质量缺陷的重要原因。2007年以来,河北钢铁集团邯钢公司第三炼钢厂采用先进的结晶器液压振动台提高振动精度,提高了板坯连铸机扇形段装配精度,解决了多项设备漏水问题,优化了铸坯矫直区配水,成功解决了高强度含铌连铸板坯表面横裂质量问题。     

Re-modeling of Laves phases in the Cr–Nb and Cr–Ta systems using first-principles results

Total energies of Laves phases Cr₂X, CrX₂, CrCr₂ and XX₂ (X=Nb,Ta) in all three structural forms C14, C15 and C36 have been calculated ab initio by pseudopotential VASP code with a complete relaxation of structural parameters. The calculated values were used in a two-sublattice model for re-modeling of Gibbs energies of Laves phases and subsequently for calculation of phase diagrams of Cr–Nb and Cr–Ta systems by CALPHAD method. It turns out that application of ab initio calculated values of total energy of hypothetical “end-members” in a two-sublattice model substantially simplifies the modeling and lowers the number of necessary parameters. Comparison of phase diagrams obtained by a model using first-principles results with previous empirical approach as well as relative stability of Cr₂X polytypes is presented.     

TEM characterization and reaction mechanism of composite coating fabricated by plasma spraying Nb–SiC composite powder

Niobium carbide composite coatings with Nb₂C, NbC, Nb₃Si as the main phases were prepared in situ on the surface of TC4 titanium alloy by plasma spraying Nb–SiC composite powder. The microstructure of the coating was characterized in detail by TEM, and the reaction mechanism of Nb–SiC was revealed. Sub-micron and nano-scale NbC grains dispersed in Nb₃Si region, nano-Nb/Nb₃Si cellular eutectic region, and equiaxed Nb₂C nanograins region were formed in the coating. The research results show that Nb and SiC reacted firstly to form cubic NbC and Nb₃Si phases during the plasma spraying process. Then, NbC with a higher melting point took the lead in crystallization during the cooling process of the coating, forming sub-micron and nano-scale NbC granular fine grains. Nb₃Si with a lower melting point crystallized around the sub-micron and nano-scale NbC granular fine grains in the subsequent cooling process. In the plasma spraying process, the molten droplets formed Nb/Nb₃Si cellular eutectic structure under large temperature gradient and extremely fast cooling rate. The remaining Nb in the raw material powder formed a diffusion couple with NbC to generate fine and dispersed nano-equiaxed Nb₂C with cubic structure. The present investigation provides a reference for the reaction synthesis of advanced nanocomposites using Nb–SiC system.     

稀土氧化物对钛酸铝陶瓷显微结构和力学性能的影响

研究了添加稀土氧化物Y2O3和Y2O3+Nd2O3对钛酸铝陶瓷的烧结温度、力学性能和显微结构的影响.结果表明,添加1%的稀土氧化物可以降低钛酸铝陶瓷的烧结温度,改善其显微结构,提高其力学性能,尤其是添加1%的复合稀土氧化物(Y2O3+Nd2O3)后,钛酸铝陶瓷的抗折强度和断裂韧性是未添加的试样的1.96倍和1.82倍.其性能提高的主要原因是由于稀土元素的细晶强化、净化界面、固溶强化、自增韧补强等作用.     

迭代目标转换因子分析光度法用于钛锆铪铌钽同时测定的研究

本文运用迭代目标转换因子分析光度法,以水杨基荧光酮(SAF)、溴化十六烷基三甲基铵体系,对Ti、Zr、Hf、Nb、Ta五组分的混合物试样及合金标样进行了分析测定,获得满意的结果.各元素的相对误差一般都小于10%.标准偏差2.34×10~(-4)～2.68×10~(-4),相对标准偏差4.64～5.70%.本文还对标准数据阵的建立、主因子数的确定等问题进行了探讨.     

NbF5前驱体化学气相沉积铌涂层的生长动力学

采用常压化学气相沉积方法在1150℃下成功制备了组织致密的金属铌涂层,沉积速率达到了250μm/h。通过对沉积后沿进气方向涂层厚度分析,确定了不同位置NbF_5、H_2、HF及Ar的摩尔分数,对数据进行拟合获得了与实验结果吻合较好的生长动力学方程。进一步分析动力学方程可知副产物HF对于沉积速率影响较大而Ar几乎没有影响。