单晶与多晶NbSi2在1023K氧化行为的对比

选择NbSi2的单晶、放电等离子烧结(SPS)多晶和电弧熔炼多晶样品在1O23K下氧化,研究了微裂纹、孔隙和晶界对NbSi2氧化行为的影响．结果表明,含有大量微裂纹的电弧熔炼多晶样品经3h氧化后完全粉化,而单晶和SPS样品经89h氧化亦未出现粉化．无论是单晶还是多晶样品,氧化产物均为Nb2O5和SiO2,生成的Nb2O5易剥落,样品的氧化动力学曲线均呈直线规律,证明NbSi2的氧化过程是一种本征无保护条件下氧元素与基体元素直接反应的过程．多晶样品的氧化速率明显高于单晶样品的氧化速率,分析表明晶界和孔隙相当于增加了氧化反应的有效面积,提出了相应模型．     

SiC/Nb/SiC扩散连接接头的界面构造及接合强度

使用Ｎｂ箔作中间层对常压烧结ＳｉＣ陶瓷进行了真空扩散连接。在最初的反应阶段，六方晶的Ｎｂ２Ｃ和Ｎｂ６Ｓｉ３Ｃｘ反应物分别在Ｎｂ和Ｓｉ侧形成。随着连接时间的增加，立方晶的ＮｂＣ和六方晶的ＮｂＳｉ２相在界面出现。试验结果表明，在１７９０Ｋ，３６ｋｓ的连接条件下所获得的扫头，其室温剪切强度达到１８７ＭＰａ，高温剪切强度超过１５０ＭＰ。     

Influence of Directional Solidification on the Creep Properties of a Binary NbSi Eutectic Alloy

The influence of directional solidification (DS) on the creep properties of the binary NbSi eutectic, Nb-18 at.% Si, consisting of Nb solid solution and the Nb₃Si silicide phase, is investigated. It is comparatively assessed with an identical alloy composition produced by means of powder metallurgy (PM). The creep behavior is determined for both materials for temperatures up to 1400°C and stresses up to 150 MPa. It is found that the DS process leads to an outstanding improvement of the creep resistance of about three orders of magnitude in terms of minimum creep rate; this significant difference can mainly be attributed to the different sizes of microstructural features (phase size in PM versus cell size in DS material). Diffusional creep may be the responsible creep mechanism in both the PM and the DS material. The activation energies that are responsible for the temperature dependence of creep are found to be very high compared with literature data. It is believed that the contribution of the two phases leads to this high creep activation energy. Comparison with a state-of-the-art single-crystalline nickel-based superalloy (CMSX 4) underpins the outstanding improvement of the creep resistance of DS NbSi eutectics.     

Nb-Ti-Si 合金表面辉光离子渗 Mo / 包埋渗 Si制备 MoSi2 涂层的研究

目的在Nb-Ti-Si合金表面制备MoSi2涂层。方法先进行辉光离子渗Mo,再进行包埋渗Si。分析温度对渗Mo层表面形貌、厚度、元素互扩散的影响,以及渗Si后涂层的表面形貌和结构。结果在1100℃进行辉光离子渗Mo,渗Mo层与基体形成了显著的互扩散。对渗Mo层进行包埋渗Si后,所形成的涂层组织致密,具有多层结构,由外向内依次为MoSi2层、NbSi2层和Nb5Si3层,在MoSi2和NbSi2层之间存在(Mo,Nb)Si2互扩散区。结论通过辉光离子渗/包埋渗的方法,可以在Nb-Ti-Si合金表面制备Mo Si2涂层,且涂层与基体呈冶金结合,结合较好。     

First-Principles Calculation of Nb2AlC/Nb Interfaces

We have performed a first-principles density functional theory method and molecular dynamics simulation on the Nb₂AlC(001)/Nb(001), Nb₂AlC(001)/Nb(110), and Nb₂AlC(001)/Nb(111) interfaces. The results show that the Nb₂AlC(001)/Nb(111) interface structure is the most stable structure of the three. The Al-Nb bonds at the Nb₂AlC(001)/Nb(111) interfaces show covalence bonding character, while the Nb-Nb interface bonds are mainly metallic. The Nb-C bonds in Nb₂AlC layers are very stable at up to 1500 K temperature and in an oxygen environment. The stable Nb₂AlC(001)/Nb(111) structure may have very good oxidation resistance for applications in high-temperature turbines.     

HYDROGEN PULVERIZATION OF Nb_3Al AND NbCr_2 ALLOYS

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Influence of Nb Diffusion Layer on Superconductivity of MgB2/Nb/Cu Wires

采用原位法粉末装管工艺(in-situ PIT),以Nb/Cu复合管作为包套材料制备了MgB2超导线材并且在氩气保护气氛中,不同温度条件下保温2h进行成相热处理。分别采用电阻-温度测试、磁矩转变测试、临界传输电流测试以及Nb-MgB2界面磁光研究等分析手段进行研究。结果表明:当热处理温度高于750℃时,在MgB2超导芯丝和Nb阻隔层之间形成一个扩散层,该扩散层的存在阻碍了电流的传输,从而导致在磁测法测试中可以检测到超导相存在,而在传输法测试中无法看到超导传输现象。说明采用Nb作为MgB2超导线带材的扩散阻隔层时其热处理温度不能高于750℃。     

电脱氧法制铌用Nb2O5阴极活性的改进

在用于熔盐电脱氧制备金属铌的Nb2O3固体阴极中添加石墨粉和CaCO3粉,研究了经烧结后阴极的成分及形貌,考查了添加剂对电脱氧反应的影响．研究结果表明,在Nb2O5固体阴极中添加适量的石墨粉或CaCO3粉可以增加烧结后阴极片的氧空位、影响Nb2O5颗粒尺寸的大小,从而提高阴极的电化学反应活性,加快电解反应的进行。     

原位合成Cr2Nb/CuCr复合材料及其真空电特性

采用真空烧结熔渗法制备不同Cr2Nb含量的Cr2Nb/CuCr复合材料.通过XRD和SEM研究复合材料的组织结构,采用SEM和高速摄影研究原位合成的Cr2Nb对复合材料表面电弧运动及表面烧蚀形貌的影响.结果表明:随着Cr-Nb复合粉末添加量的增加,Cr2Nb/CuCr复合材料的硬度、电导率、截流值、电弧寿命和耐电压强度均有明显改善,当Cr-Nb复合粉末的添加量为7％(质量分数)时,Cr2Nb/CuCr复合材料的阴极斑点更为分散,截流值显著降低,电弧寿命明显延长.与常规CuCr合金性能相比,Cr2Nb/CuCr复合材料表现出较好的综合性能.     

Pulsed current activated combustion synthesis and consolidation of ultrafine NbSi2 from mechanically activated powders

Dense ultrafine NbSi₂ was synthesized using the pulsed current activated combustion synthesis (PCACS) method within 2 min and in one step from mechanically activated powders of Nb and 2Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense NbSi₂ with a relative density of up to 98 % was produced under simultaneous application of a 60 MPa pressure and a pulsed current. The average grain size and mechanical properties (hardness and fracture toughness) of the compound were investigated.     

Effect of Nb on oxidation behavior of high Nb containing TiAl alloys

The isothermal oxidation behavior of Ti-45Al-8Nb and Ti-52Al-8Nb alloys at 900 °C in air was investigated. The early oxidation behaviors were studied by using XPS and AES. And the microstructure and the composition of the oxidation scale were studied by using XRD and SEM. The results show that the oxidation behavior of TiAl alloy is significantly improved by Nb addition. Nb substitutes for Ti in TiO₂ as a cation with valence 5, and thus to suppress TiO₂ growth. The (Ti,Nb)O₂-rich layer is a dense and chemically uniform which is more protective than the TiO₂ layer. Nb addition also lowers the critical Al content to form an external alumina. Nb₂Al phase is formed in the metallic matrix at the oxide–metal interface on the high Nb containing TiAl alloys.     

Mo对NbCr2/ Nb合金组织及性能影响

采用机械合金化+热压工艺制备了NbCr_2/Nb-XMo (X=0,2.5,5.0,7.5,10, at%)合金,研究了合金元素Mo对NbCr_2/Nb合金组织及性能的影响。结果表明:合金元素Mo主要存在于Nb基体中,对合金的物相不产生明显影响,合金仍由Nb固溶体和NbCr_2组成;Mo的添加使得NbCr_2/Nb的相界面处应力增加,导致NbCr_2颗粒中的层错/孪晶的密度增加,并促进了Nb基体中位错的运动,从而使得NbCr_2/Nb合金在保持高强度的同时,具有良好的塑性和韧性。     

Isothermal oxidation behavior of powder metallurgy beta gamma TiAl–2Nb–2Mo alloy

A new TiAl–2Nb–2Mo beta gamma alloy was synthesized by powder metallurgy process. HIP’ed and vacuum heat treated specimens were isothermally oxidized at 800 °C and 900 °C in air up to 500 h. The TiAl–2Nb–2Mo alloy oxidized parabolically up to 500 h at both 800 °C and 900 °C. The oxides consisted of outer TiO₂ layer, intermediate Al₂O₃ layer, and inner TiO₂ rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of lamellar colonies formed a diffusion zone just below the oxide/substrate interface consisting of γ-TiAl matrix and dispersed beta phases which contained high concentration of Nb and Mo. The oxidation rate of the TiAl–2Nb–2Mo alloy is more sensitive to temperature than those of the Ti–48Al–2Nb–2Cr and Ti–48Al–2Nb–2Cr–W alloys.     

Nb元素的添加对Fe-Co-2V软磁合金微观结构的影响

Fe-49Co-2V与Fe-49Co-2V-0.3Nb合金经热轧、冷轧制成带材,之后在850 ℃进行2 h退火热处理。使用透射电镜和选区电子衍射对合金微观组织结构进行观察,结果表明Nb元素的添加促进了析出相的形成,析出相为Nb与Co、Fe组成的小尺寸晶粒,不含V元素,其化学式为Co₃Nb,其中部分Co原子被替换为Fe原子。在铸态样品中同样发现了形态不同的析出相,推测可能是带材中析出相的来源。在添加Nb元素的合金中发现条纹状孪晶结构且集中于析出相附近,推测可能与合金伸长率升高及晶粒细化有关。     

低稀土含量的纳米复相α-Fe/Nd2Fe14B淬态合金微结构与微波电磁特性研究

对低稀土含量的Nd6Fe91B3合金进行熔体快淬处理,制备了由a-Fe相和少量的Nd2Fe14B相组成的纳米复相材料,并对其进行球磨处理25 h.研究了快淬速度对淬态合金的相组成、微观结构、微波电磁性能的影响规律.研究结果表明,随着淬度的提高,淬态合金中高磁晶各向异性的Nd2Fe14B相逐渐减少,材料的自然共振频率向低频移动,但样品微波磁导率随淬速的提高而升高.淬速为40 m/s的样品微波磁导率虚部在4.17 GHz获得最大值μrmax=4.66,其实部在1.55 GHz获得最大值μmax =7.88.同时,低稀土含量的纳米复相α-Fe/Nd2Fe14B材料具有良好的微波电特性,其复介电常数在2 GHz附近出现共振.由于磁损耗和电损耗共同作用,有利于该材料在GHz频段电磁波吸收材料中的应用.     

Nb、Al共掺杂MoSi2弹性性质的第一性原理计算

通过第一性原理计算研究了Nb、Al共掺杂MoSi2晶体的电子结构、弹性常数和Mullikan布居数。结果表明,Nb、Al共掺杂可大幅提高MoSi2的韧性和导电性,当Nb和Al共掺杂量达到x=0.25时,MoSi2的弹性模量从408.86GPa降低到261.30GPa。MoSi2的电子态密度和Mullikan布居数分析表明,Nb和Al掺入后MoSi2电子态密度发生蓝移,费米能级处的电荷密度增加,体系的导电性能提高。掺杂后Mo-Al、Nb-Si键布居数减小,键长增大,原子间的共价性减弱,而Al-Si键间的共价性增强。晶体中各方向键长和键能的分布趋于对称化,MoSi2晶体韧性增强。     

Nb—Ti—Si三元系1473K等温截面的测定

运用扩散偶技术结合电子探针微区成分分析方法对Nb-Ti-Si三元扩散偶进行相分析，测得Nb-Ti-Si三元系1473K下所生成的7个扩散层，分别是TiSi2,TiSi,Ti5Si3,Nb5Si2和M3Si，此扩散偶中未发现三元化合物，并根据扩散偶中的相区分布和相图中相区分布的关系，得出Nb-Ti-Si三元系1473K下的等温截面。     

去除Ta2O5/Nb2O5中杂质S的工艺研究

从理论和实际应用方面,研究了去除Ta2O5/Nb2O5中杂质S的方法.通过对制取高纯Ta2O5和Nb2O5的中间产品高纯Ta（OH）5/Nb（OH）3进行过氧化处理,改变Ta,Nb,S等元素在物料中的存在方式,增大了含S杂质的溶解性,降低了物料对含S离子的吸附能力及硫酸盐的分解温度,通过洗涤、焙烧达到有效去除产品中杂质元素S的目的.该方法可在不影响Ta2O5/Nb2O5产品质量的情况下,使杂质S降低到0.0001%以下.     

添加Nb元素对Sm2Fe17合金微结构的影响

通过氢化-歧化-脱氢-重组法制备Sm2(Fe，M)17(M=Nb)合金，探讨了添加合金元素Nb对Sm2Fe17合金的微结构的影响。通过扫描电子显微镜和能谱仪、X射线衍射仪等分析手段对Sm2(Fe，M)17(M=Nb)进行测试和分析表明：添加微量的Nb元素可以有效的改善Sm-Fe合金铸态组织的显微结构。     

SEPARATION OF Ta AND Nb BY EXTRACTION WITH SEC-OCTANOL-HF-H_2SO_4 SYSTEM

ＳＥＰＡＲＡＴＩＯＮＯＦＴａＡＮＤＮｂＢＹＥＸＴＲＡＣＴＩＯＮＷＩＴＨＳＥＣ－ＯＣＴＡＮＯＬ－ＨＦ－Ｈ_２ＳＯ_４ＳＹＳＴＥＭ￥ＣｈｅｎＨｕｉｆａｎｇ；ＨｅＷａｎｎｉａｎ；ＺｈａｎｇＹｕｑｉ（ＢｅｉｊｉｎｇＧｅｎｅｒａｌＲｅｓｅａｒｃｈＩｎｓｔｉｌｕｔ...