纳米晶Ti(C,N)固溶体粉末的制备及组织结构研究

研究了纳米晶Ti(C,N)固溶体粉末的碳热还原反应制备及其组织结构特征。结果表明．以球形亚微米TiO2粉末和纳米碳黑为原料，通过原料成分C／Ti的准确配比和适当的工艺参数，可制备出成分优良的晶粒度为37nm的单相纳米晶Ti(C，N)固溶体粉末。     

不同Nb含量对(Nb,Ti)C颗粒强化Fe基复合堆焊层微观组织及耐磨性影响研究

目的 颗粒强化金属基复合涂层由于具有优异的力学性能及良好的耐磨性,受到了研究人员的广泛关注,然而,较少有文献报道复合强化相含量与复合涂层力学性能的关系,特别是在电弧堆焊制备的复合涂层中。因此,有必要探明强化颗粒含量对Fe基复合堆焊涂层微观组织及耐磨性的影响规律,为设计新型Fe基复合堆焊材料提供试验依据。方法 通过向药芯焊丝中添加不同含量的Nb,以原位合成(Nb,Ti)C强化相,并据此调控电弧堆焊层中原位生成的(Nb,Ti)C数量密度,进而影响堆焊层的微观组织、硬度及耐磨性。结果 随着Nb的添加,熔覆过程中Nb与基体中的C、Ti反应,原位生成了立方结构的(Nb,Ti)C相,且(Nb,Ti)C相含量随着Nb含量的增加而逐渐增大。与未添加Nb时相比,含质量分数为6% Nb的堆焊层中(Nb,Ti)C复合颗粒的数量密度增加到0.53个/μm²,硬度也由673.08HV0.5增大到734.88HV0.5。摩擦磨损试验结果表明,随着Nb的增加,磨损量呈现出逐渐降低的趋势,其中,Nb含量为6wt.%的堆焊层样品表现出了最浅、最平滑的磨痕,其磨损率仅为1.12×10^?8 mm³/(N.m),磨损机制为轻微的黏着磨损。结论 提高Nb的添加量可以增大(Nb,Ti)C强化相的数量密度,有效提升堆焊层的硬度及耐磨性,并在添加质量分数为6%的Nb时表现出最高的耐磨性能。     

Structural and electrical conductivity studies on rutile solid solutions [FexTi1-2xMxO2 (M=Nb, Ta)]

In this study, FexTi1-xMxO2 (M=Nb, Ta; 0x0.5) solid solutions have been synthesized from both ceramic and gel methods, and electrical and structural characterization hasbeen carried out. The solid solutions show rutile structure except for the case of FeNbO4, which forms an orthorhombic structure. The electrical behaviour of the system studied corresponds to extrinsic p-type semiconduction and it is related to the presence of Fe(II) ions. Conductivity is enhanced by local distortions of the M–O lengths associated with ordering oxidation states such as those in Fe3O4. The distortions are more frequent when the asymmetry is greater (M=Nb). No electrical changes have been detected when the synthesis method is different. © 1998 Kluwer Academic Publishers     

Characterization and dielectric properties of Sr4La2Ti4M6O30 (M=Nb, Ta) ceramics

Sr₄La₂Ti₄M₆O₃₀ (M=Nb or Ta) compounds were synthesized by the conventional powder compaction and high temperature solid state reaction technique. The dielectric properties of the sintered samples were measured and they were further characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Sr₄La₂Ti₄M₆O₃₀ compounds are paraelectric phases adopting filled tetragonal tungsten–bronze (TB) structure at room temperature. Sr₄La₂Ti₄Nb₆O₃₀ and Sr₄La₂Ti₄Ta₆O₃₀ show high dielectric constants of 387 and 166 together with low dielectric loss of 0.0084 and 0.0042 at 1 MHz, respectively.     

Electromagnetic wave absorbing properties of TMCs (TM=Ti,Zr, Hf,Nb and Ta) and high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C

Electromagnetic wave (EMW) absorbing materials play a vital role in modern communication and information processing technologies to inhibit information leakage and prevent possible damages to environment and human bodies.Currently,most of EMW absorbing materials are either composites of two or more phases or in the form of nanosheets,nanowires or nanofibers in order to enhance the EMW absorption performance through dielectric loss,magnetic loss and dielectric/magnetic loss coupling.However,the combination of complex shapes/multi phases and nanosizes may compound the difficulties of materials processing,composition and interfaces control as well as performance maintenance during service.Thus,searching for single phase materials with good stability and superior EMW absorbing properties is appealing.To achieve this goal,the EMW absorbing properties of transition metal carbides TMCs (TM=Ti,Zr,Hf,Nb and Ta) and high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C which belong to ultrahigh temperature ceramics,were investigated in this work.Due to the good electrical conductivity and splitting ofd orbitals into lower energy t2g level and higher energy eg level in TMC6 octahedral arrangement,TMCs (TM=Ti,Zr,Hf,Nb and Ta) exhibit good EMW absorbing properties.Especially,HfC and TaC exhibit superior EMW absorbing properties.The minimum reflection loss (RLmin) value of HfC is -55.8 dB at 6.0 GHz with the thickness of 3.8 mm and the effective absorption bandwidth (EAB) is 6.0 GHz from 12.0 to 18.0 GHz at thickness of 1.9 mm;the RLmin value of TaC reaches-41.1 dB at 16.2 GHz with a thickness of 2.0 mm and the EAB is 6.1 GHz with a thickness of 2.2 mm.Intriguingly,the electromagnetic parameters,i.e.,complex permittivity and permeability are tunable by forming single phase solid solution or high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C.The RLmin value of high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C is -38.5 dB at 9.5 GHz with the thickness of 1.9 mm,and the EAB is 2.3 GHz (from 11.3 to 13.6 GHz) atthickness of 1.5 mm.The significance of this work is that it opens a new window to design single phase high performance EMW absorbing materials by dielectric/magnetic loss coupling through tuning the conductivity and crystal field splitting energy of d orbitals of transition metals in carbides,nitrides and possibly borides.     

Research on in situ synthesised (Ti,V)C/Fe composite coating by laser cladding

Laser cladding is an effective way to improve the wear resistance of mechanical components. In this study, the composite carbide (Ti,V)C reinforced Fe based coating was successfully synthesised by laser cladding the powder mixtures of ferrotitanium, ferrovanadium and graphite. The samples were analysed to assess the microstructure, microhardness and wear properties. Results indicate that high quality composite coating with metallurgical joint to the steel substrate was obtained. During laser cladding processes, it is found that the (Ti,V)C composite particles were in situ synthesised and distributed evenly in the coating. The microhardness and wear properties of the clad coating were improved significantly in comparison to the steel substrate due to the presence of the hard reinforcement (Ti,V)C.     

Electrical properties of BaTi1−x M x O3 (M = Nb, Ta, Mo, W) ceramics

The electrical properties of BaTi_1?x M _x O₃ (M = Nb, Ta, Mo, W) ceramics (partial substitution of Group V (Nb, Ta) or VI (Mo, W) metals on the titanium site) have been studied by impedance spectroscopy. The results indicate that the Group VI metals (Mo and W) are less effective as donor dopants of barium titanate than are Nb and Ta because most of the Mo and W ions reside in the outer layer of the grains, raising its resistance.     

Ti(C,N)材料的研究进展

分别介绍了Ti(C,N)陶瓷材料、Ti(C,N)基金属陶瓷材料和Ti(C,N)基复相陶瓷材料的组织结构、性能、优势及其制备方法。Ti(C,N)陶瓷材料的制备方法主要有气相沉积法、激光熔覆法和自反应喷涂法,Ti(C,N)基金属陶瓷材料的制备方法主要有粉末冶金法和自蔓延高温合成法,Ti(C,N)基复相陶瓷材料的制备方法主要有自反应喷射成形法和自反应喷涂法。最后介绍了Ti(C,N)材料的应用及其应用的局限性。     

Ti(C,N)基金属陶瓷的研究进展

介绍了Ti(C,N)基金属陶瓷的晶体结构和高温力学性能,综述了其主要制备方法和研究进展,详细地分析了其冶金机理和相结构特点,并讨论了环型相的形成机理及缺点,最后指出了Ti(C,N)基金属陶瓷研究方向和提高其性能的基本途径,并认为系统考虑其相平衡、粉末冶金机制和加工工艺是制备性能优良的Ti(C,N)基金属陶瓷刀具和涂层的关键.     

Varied roles of Pb in transition-metal PbMO3 perovskites (M = Ti,V, Cr,Mn, Fe,Ni, Ru)

Different structural chemistries resulting from the Pb²⁺ lone-pair electrons in the PbMO₃ perovskites are reviewed. The Pb²⁺ lone-pair electrons enhance the ferroelectric transition temperature in PbTiO₃, stabilize vanadyl formation in PbVO₃, and induce a disproportionation reaction of Cr^IV in PbCrO₃. A Pb²⁺ + Ni^IV = Pb⁴⁺ + Ni^II reaction in PbNiO₃ stabilizes the LiNbO₃ structure at ambient pressure, but an A-site Pb⁴⁺ in an orthorhombic perovskite PbNiO₃ is stabilized at modest pressures at room temperature. In PbMnO₃, a ferroelectric displacement due to the lone pair electron effect is minimized by the spin–spin exchange interaction and the strong octahedral site preference of the Mn^IV/III cation. PbRuO₃ is converted under pressure from the defective pyrochlore to the orthorhombic (Pbnm) perovskite structure where Pb–Ru interactions via a common O −2p orbital stabilize at low temperature a metallic Imma phase at ambient pressure. Above P_c a covalent Pb–Ru bond is formed by Pb²⁺ + Ru^IV = Pb⁴⁺ + Ru^II electron sharing.     

Structures and electronic properties of M2C2 @ C78 (M = Ti, Zr, Hf): a density functional theory study

A systematic DFT investigation has been conducted to explore the structures and electronic properties of the metal-carbide endofullerenes M2C2 @ C78 (M = Ti, Zr, Hf) at the PBE/DNP level of theory. The theoretical calculations predicted the following: (i) this series of endofullerenes have the valence states [M4+]2C2(2-) @ C78(6-) (ii) the structure of the [M2C2](6+) cluster encapsulated in the C78(6-) (D3h) cage varies with the increasing of the ionic radius of M4+, i.e., from a linear M-C [triple bond] C-M geometry for M = Ti, through a zigzag geometry for M = Hf to a side-on binding mode for M = Zr; (iii) M2C2 @ C78 (M = Zr, Hf) should display interesting intramolecular dynamic behavior at room temperature, i.e., the encapsulated C2(2-) moiety can rotate freely around the C3-axis of the C78(6-) (D3h) cage; (iv) the [Ti2C2]6+ in the lightest Ti2C2 @ C78 is far more fixed by adopting the linear Ti-C - C-Ti geometry; (v) the order for their ionization potentials is Ti2C2 @ C78 < Hf2C2 @ C78 < Zr2C2 @ C78, whereas their EAs follow the order: Ti2C2 @ C78 < Hf2C2 @ C78 approximately Zr2C2 @ C78. The predicted redox properties of these endofullerenes suggest that Zr2C2 @ C78 is synthetically as approachable as Hf2C2 @ C78.     

Carbon nanotube formation over laser ablated M and M/Pd (M = Fe,Co, Ni) catalysts: The effect of Pd addition

Monometallic and bimetallic M and M/Pd (M = Fe, Co, Ni) nanoparticles were prepared by pulsed Nd:YAG laser ablation of bulk M and Pd targets in acetone and transferred onto Si wafers to catalyze carbon nanotubes from decomposition of liquid petroleum gas via thermal chemical vapor deposition at 750°C. Transmission electron microscopy and optical extinction study revealed that the prepared M and M/Pd nanoparticles have rather spherical shape and their aspect ratios are nearly one. In comparison to monometallic M catalysts by addition of Pd, the average sizes of produced bimetallic M/Pd catalysts increased. Carbon nanotubes' characterization revealed that by addition of Pd to laser ablated M catalysts the average diameter, the yield, and quality of end product carbon nanotubes were increased. The average diameter of grown carbon nanotubes increases as: Ni < Ni/Pd < Co < Co/Pd < Fe < Fe/Pd and the quality of them increases as: Ni < Co < Fe < Ni/Pd < Fe/Pd < Co/Pd.     

Nanocrystallization in Fe73.5Si13.5B9Cu1Nb1X2 (X = Nb,Mo and V) alloys studied by X-ray synchrotron radiation

The influence of partial substitution of Nb by refractory elements (Mo and V) on the nanocrystallization process of a FeSiB-CuNb alloy was studied by in situ X-ray diffraction, using a synchrotron radiation source. The crystalline volume fraction, the mean grain size of the crystallites and the nanophase Si content were estimated to describe the microstructural evolution and the kinetics of the process. For the studied alloys, the volume fraction of the Fe,Si nanophase after annealing at the same condition increases in the order Nb < Mo < V. The mean grain size of the Fe,Si nanocrystals also increases in the sequence Nb < Mo < V. Transformation kinetics is described in terms of Johnson-Mehl-Avrami kinetics (JMA) and the obtained values for the overall Avrami exponent are slightly below 1, as usually found for Finemet alloys.     

Phase formation, sintering behavior and microwave dielectric properties of bismuth and manganese co-doped [(Pb, Ca) La](Fe, Nb)O3+δ solid solution

The phase formation, sintering behavior and microwave dielectric properties of Bi₂O₃ and MnO₂ co-doped [(Pb, Ca) La](Fe, Nb)O_3+δ (PCLFN) ceramics were investigated. The Bi₂O₃ and MnO₂ binary dopants formed stable and low melting temperature solubilities at grain boundary which resulted in an effectively lowered sintering temperature by about 140 °C a more rapid sintering process and enhanced bulk densities. Sintering procedure has significant effect on grain size and porosities in ceramics. With high sintering temperature and time, the evaporation of PbO scaled up from surface toward the bulk and resulted in a Pb²⁺ deficient layer up to 0.25 mm depth under ceramic surface. Investigation of sintering dynamic revealed that either volume diffusion or second-order interface mechanism controlled the grain growth in present system. An optimal microwave dielectric properties of ε_r = 91.1, Q _f = 4,870 GHz and τ _f = 18.5 ppm/°C could be obtained in Bi₂O₃ and MnO₂ co-doped [(Pb, Ca) La](Fe, Nb)O_3+δ ceramics sintered at 1,050 °C for 4 h when the quality ratio of Bi₂O₃/MnO₂ was 1 and the doping content w = 1 wt%.     

MgNi-TiNi0.56M0.44（M=Al、Fe）贮氢合金的制备和电化学性能研究

用机械合金化法制备出MgNi及MgNi-TiNi_0.56M_0.44（M=Al、Fe）复合合金,并研究该系列合金的相结构和电化学性能. XRD结果表明所合成的几种合金均为非晶态;充放电结果表明：MgNi-TiNi_0.56M_0.44（M=Al、Fe）复合合金的初始容量比纯MgNi合金低,但循环寿命有较大的改善,其中MgNi-TiNi_0.56Al_0.44合金放电容量最大,达380.64mAh/g,经50次循环后容量保持率是48.97％;动电位扫描结果表明复合后合金电极的抗腐蚀能力增强;循环伏安法和电化学阻抗谱法研究结果表明：复合后降低了电极表面的电子转移电阻和H原子的扩散阻抗,增强了电极表面的电化学催化性能.     

Magnetic anisotropy in Sm2Fe17-xMx (M = Al, Ga) and (Sm1-xTmx)(2)Fe14Al3

1. IntroductionMany illtermetajlic compounds of R-Fe and R-Co(R: rare earths) have some ideal properties as highquality permanent magnet materials where a largemagnetic anisotropy of 4f electrons is coupled withstrong exchange interaction of 3d electrons via the4f-3d illteraction.In 1967 the SmCos magnet was discovered as thefirst rare earth permanent magnet, and in 1973 moreimproved magnet in the form of SmZCo17 was developed, These two compounds were found to have excellellt permanellt m…     

Order-disorder transformation of the body centered cubic phase in the Ti-Al-X (X = Ta, Nb, or Mo) system

The ordering of the bcc phase present in the Ti-Al-X (X = Ta, Nb, or Mo) system is investigated in this paper. There is a ternary phase of ordered bcc (B2) structure near the composition Ti-25Al-25X. All compositions mentioned in this paper are in atomic percent, unless mentioned otherwise. The phase reactions in Ti-33Al-17Ta alloy are examined in detail following solidification and solid-state processing treatments. It can be found from the differential thermal analysis (DTA) that the B2 phase in this alloy is stable up to 1205°C, where it experiences a solid-state order to disorder transformation. The rate of this ordering reaction is so high that it cannot be arrested by rapid solidification processing (RSP). The presence of thermal antiphase boundaries (APBs) in the microstructure confirms the solid-state ordering of the B2 phase from the disordered bcc phase. Ordering reactions involving the bcc phase in the Ti-Al-Nb and Ti-Al-Mo systems are also studied because of their similarity with the Ti-Al-Ta system. It can be found that they are also solid-state ordering reactions. In the Ti-25Al-25Nb alloy the B2 phase is ordered up to 1141°C; whereas in the Ti-25Al-25Mo alloy the B2 phase is ordered up to 1418°C.     

Ti,Nb和W复合强化超纯铁索体不锈钢的高温析出行为

为提高汽车尾气排放系统中高温端排气歧管等所用铁素体不锈钢的综合性能,采用真空熔炼制备Ti,Nb和W复合强化的超纯铁素体不锈钢(不含Ni),并利用硬度和力学性能测试、场发射扫描电子显微镜和透射电子显微镜分析研究固溶态材料在550,600℃和700℃的时效硬化规律、拉伸性能以及时效析出行为.600℃时效40h之后材料力学性能达到最佳值,在晶粒内部和晶界区域弥散分布着两种形态的纳米析出相,一种是呈不规则颗粒状的(Ti,Nb)C,另一种是呈长条状的Laves相Fe2(Nb,W);这两种析出相与铁素体基体均存在固定的晶体学取向关系,即[011]Fe∥[011](Ti,Nb)c和(0(-1)1)Fe∥(200)(Ti,Nb)C(晶面偏差约3°)以及[011]Fe∥[0001]Fe2(Nb,w)和(200)Fe∥(01(-1)0)Fe2(Nb,w)(晶面偏差4°～5°).随时效温度提高,析出相的尺寸增大,且析出相由(Ti,Nb)C逐渐转变为Fe2 (Nb,W).