快凝Al92.3Fe4.3V0.7Si1.7Nd1.0纳米晶合金电场时效过程研究

研究了快凝Al92.3Fe4.3V0.7Si1.7Nd1.0纳米晶合金薄带在电场时效过程中组织和力学性能的变化,并与等温时效处理结果进行比较,结果表明：电场时效处理试样的相转变温度降低,力学性能有所提高。对电场作用机理进行了初步分析。     

单相Sm5Co2纳米晶合金的制备及其性能研究

以Sm₅Co₂合金为例,提出了富Sm型单相纳米晶结构的Sm-Co合金的制备方法.物相分析和显微组织观测表明,Sm₅Co₂合金只含有纯净的单斜结构Sm₅Co₂相,晶粒组织细小均匀,平均晶粒尺寸约为10 nm.在此基础上,对制备的单相Sm₅Co₂纳米晶合金块体材料的磁性能和力学性能进行了全面表征和分析.结果表明,与同种成分的粗晶合金相比,纳米晶Sm₅Co₂合金的磁性能明显提高.且硬度和弹性模量均有不同程度增加.     

热处理工艺对高BsFe84B6P6C3Cu1纳米晶合金磁电性能的影响

以Fe₈₄B₆P₆C₃Cu₁非晶合金为基础,系统研究了热处理工艺参数对合金晶化行为、电阻率ρ以及软磁性能的影响规律。结果表明,当退火温度位于第一晶化峰开始温度T_x1和第二晶化峰开始温度T_x2之间时,α-Fe晶粒的形核速率随退火温度的升高而增大,晶粒尺寸随退火温度的升高而减小。α-Fe晶粒尺寸的细化和体积分数的增加有利于合金条带的矫顽力H_c降低,饱和磁通密度B_s和有效磁导率μ_e提高。ρ随退火温度的变化规律表明,结构弛豫退火会使合金ρ轻微下降,但是α-Fe晶粒的析出会使合金ρ快速降低,而Fe₃(B, P)化合物相的析出会导致合金ρ的再次快速增大。通过对合金条带在不同温度和时间退火后的软磁性能和显微结构研究发现,退火温度的升高会增大软磁性能对退火时间的敏感性,即缩短合金条带的最佳退火时间范围,合金在420、450和480℃的最长最佳退火时间分别为60、3...     

纳米晶SmCo7合金的相失稳及伴随的晶粒长大

采用放电等离子烧结(SPS)技术制备出致密的纳米晶单相SmCo7合金块体。以此纳米晶合金为初始材料,通过系列退火实验系统研究其晶格参数、物相组成和显微组织随晶粒长大的演变特征。结果表明:纳米晶SmCo7相(1:7H)从室温至600℃都能保持很好的相稳定性和热稳定性。通过XRD分析和TEM观察证实,纳米晶SmCo7相的失稳分解和晶粒的突发长大是伴随发生的,即在较高温度(高于600℃)条件下纳米化稳定的SmCo7相会分解为Sm2Co17相(2:17R)和SmCo5相(1:5H),同时晶粒组织会急剧粗化;其中SmCo5相会以圆形析出物的形式均匀分布于晶界处和晶粒内部;随着晶粒的长大,六方结构的纳米晶SmCo7相的晶格参数a和单胞体积均线性减小,而轴比c/a则变化不大。     

基于晶化动力学对Co70Fe10Si9B7Cu1Nb3非晶合金软磁性能的调控

钴基非晶合金作为应用广泛的软磁材料具有高磁导率、低矫顽力等优点,但饱和磁感应强度普遍偏低。为此,采用单辊急冷法制备Co₇₀Fe₁₀Si₉B₇Cu₁Nb₃非晶合金薄带,通过晶化动力学的计算对其晶化行为进行分析,并合理制定退火温度,实现对Co₇₀Fe₁₀Si₉B₇Cu₁Nb₃非晶合金软磁性能的调控。结果表明：Co₇₀Fe₁₀Si₉B₇Cu₁Nb₃非晶合金晶化反应过程中起始晶化反应激活能E_x1大于峰值晶化反应激活能E_p1,即晶体的形核过程比晶体长大过程更困难,但起始晶化反应温度T_x要低于峰值晶化反应温度T_p,因此选择...     

退火温度对Fe64Co16Zr7B12Cu1纳米晶合金软磁性能的影响

在Hitperm合金基础上制备了成分为Fe64Co16Zr7B12Cu1的非晶纳米晶合金带,并对其组织特征及软磁性能进行了研究。结果表明:Fe64Co16Zr7B12Cu1合金具有较好的非晶形成能力和热稳定性;非晶态合金随着温度的升高晶化程度增加,断裂方式逐渐转变为沿晶断裂。合金经过适当的热处理后,饱和磁感应强度Bs和最大磁导率μm均有一定提升,最高分别达到Bs=1.47T,μm=2.67×104。     

初生纳米晶对Ti40Zr25Ni8Cu9Be18非晶合金结构稳定性的影响

通过感应熔炼喷铸法制备具有非晶/纳米晶复合结构的块体Ti40Zr25Ni8Cu9Be18合金。在与全非晶结构的Ti40Zr25Ni8Cu9Be18合金进行比较的基础上,研究Ti40Zr25Ni8Cu9Be18非晶/纳米晶合金在均匀流变过程中的晶化程度,分析其在连续升温过程中的晶化动力学。结果表明:初始纳米晶的存在不会明显降低非晶/纳米晶合金在过冷液相区流变过程中的结构稳定性;非晶/纳米晶合金的晶化激活能约为233.21 kJ/mol,与非晶合金的晶化激活能大致相同;随着转变分数的增加非晶/纳米晶合金的局部Avrami指数从2变化到0.5,明显低于非晶合金的局部Avrami指数;这表明初始纳米晶并没有明显加速非晶的晶化过程。     

Al9Fe0.7Ni1.3相对喷射沉积Al-Zn-Mg-Cu-Ni合金组织和性能的影响

本文利用喷射沉积技术合成含Ni的Al-Zn-Mg-Cu合金,合金中的Ni元素以亚微米球状Al₉Fe_0.7Ni_1.3化合物的形式存在。利用扫描电镜和电子背散射衍射、透射电镜以及拉伸测试研究了Al₉Fe_0.7Ni_1.3颗粒对合金固溶处理后组织和性能的影响。结果发现：Al₉Fe_0.7Ni_1.3颗粒主要在晶界附近分布,说明该颗粒在固溶过程中具有有力的抑制再结晶作用。固溶处理后,合金的拉伸强度为603 MPa,断裂延伸率为11.79%,主要断裂方式为穿晶延性断裂。实验结果表明亚微米球状Al₉Fe_0.7Ni_1.3化合物对合金性能有重要影响,可以产生细晶强化和Orowan强化,是合金发生穿晶延性断裂的主要原因。     

时效工艺对Ni75Al15Ti10合金沉淀过程的微观相场模拟

本文通过微观相场动力学模型模拟了Ni₇₅Al₁₅Ti₁₀合金的沉淀过程。首先通过原子演化图发现,沉淀过程分为两步,起初为L1₀相向L1₂相的转变,随后为化学计量比L1₂相的形成。随后研究了单级时效温度对微结构,原子占位以及原子扩散的影响,结果表明：随着温度升高无规则形状的γ′相变为规则立方体状并且择优取向显著;同时Al原子从γ′相界面向内部扩散,Ti原子正好相反。但是温度越高,原子占位以及有序化程度越低。为了提高γ′相的原子占位,我们进一步比较了双级时效对γ′相的影响。发现双级时效不仅能获得规则排列稳定的γ′相,同时还可以提高Al与Ti原子在其正位处的原子占位并抑制反位缺陷的产生。我们的实验结果在一定程度上为制备具有优异力学性能的Ni-Al-Ti合金提供了理论依据。     

离子辐照对Zr50.7Cu28Ni9Al12.3非晶合金力学性能的影响

非晶合金有潜力成为新一代核材料,离子辐照对其力学性能的影响决定了其使用价值。在不同剂量的Au离子辐照下,探讨了Zr_(50.7)Cu_(28)Ni_9Al_(12.3)非晶合金力学性能的变化过程。原子力显微镜以及正电子湮没寿命谱分析表明,在离子辐照后,非晶合金的自由体积尺寸增大、密度下降,总自由体积增加。透射电子显微镜分析表明,辐照剂量在达到50 dpa时非晶合金开始有纳米晶析出,随着辐照剂量的增加,纳米晶尺寸在增加、密度变大。纳米压痕试验表明,离子辐照后非晶合金的硬度减小,在高剂量时硬度又有增加的趋势。离子辐照下非晶合金的硬度变化是自由体积以及纳米晶竞争的结果。自由体积使非晶合金软化,纳米晶析出使非晶合金硬化。     

Al3V表面氧吸附的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算了低指数Al3V表面的表面能,分析其稳定性;然后采用最稳定表面研究了Al3V表面的O吸附行为以及合金元素的影响。结果表明,终止于Al原子的(110)面是最稳定的表面。O原子倾向于吸附在(2×1)-(110)-Al表面桥位,且随着覆盖度增加,O吸附的稳定性增加。从DOS分析和O与表面各原子的间距可以推断,该表面在氧化的初始阶段发生Al的氧化和V的内氧化,氧化后有可能形成具有保护性的Al2O3膜。合金元素Ti和Cr均倾向于占据表面第2层V原子位,且都促进O原子在表面的吸附,但2者的作用机制不同,Ti与O相互作用较强,从而降低了Al与O的相互作用,在氧化过程中Ti与Al有可能同时氧化,从而形成Al和Ti的混合氧化物;Cr对于Al和O的相互作用有微弱的增强作用,使得O的吸附更加稳定,可能会促进Al的氧化,从而形成保护性的Al2O3。     

An Al13Fe4 phase in the Al---Cu---Fe alloy system

The Cu-containing Al₁₃Fe₄ phase was studied by X-ray diffractometry, electron microscopy and thermal analysis. The increase in the Cu concentration results in a decrease in the melting temperature. No structural variations were observed in this compound up to a limiting Cu concentration of about 6 at.%. The increase in the Cu content is realized by the permanent replacement of the Al atoms by Cu in the (xOz) plane of the binary Al₁₃Fe₄ structure at the (0.5, 0, 0.5) and (0.919, 0, 0.216) positions as determined for the 4 at.% Cu phase. The effect of the substitution of Cu for Al is discussed with respect to the absorption of electrons by Fe atoms in (Al, Cu)₁₃Fe₄.     

Formation and crystallization of an amorphous Al80Fe10Ti5Ni3B2 alloy

In this study, we investigated the crystallization behavior of an Al₈₀Fe₁₀Ti₅Ni₃B₂ amorphous alloy (obtained by mechanical alloying) using X-ray diffraction (XRD), transition electron microscopy (TEM), and differential thermal analysis (DTA) techniques. The obtained results show that an amorphous phase formed during mechanical alloying (for 40 h) of the Al-10%Fe-5%Ti-3%Ni-2%B powder mixture. It was found that the Al₈₀Fe₁₀Ti₅Ni₃B₂ amorphous alloy exhibits one-stage crystallization when heated (amorphous to Al₁₃Fe₄, Al₅Fe₂ and AlFe intermetallic phases). The activation energy for the crystallization, evaluated from the Kissinger equation, was about 242 ± 5 kJ/mol. We also discuss kinetic parameters such as the Avarmi exponent and reaction order (n). The results show that only one three-dimensional diffusion-controlled growth mechanism was working during the amorphous-glass process of the investigated glass.     

Assessment of the surface state behaviour of Al71Cu10Fe9Cr10 and Al3Mg2 complex metallic alloys in sliding contacts

Electrochemical measurements and friction measurements during continuous and intermittent unidirectional sliding tests are used to monitor and to evaluate the surface characteristics of two types of metallic materials characterized by a huge unit cell, namely Al₇₁Cu₁₀Fe₉Cr₁₀ and Al₃Mg₂. The modification of the surface characteristics results from the periodic mechanical removal of a surface film during sliding, and the subsequent (electro)chemical re-growth of a surface film in-between successive sliding contacts. Al₇₁Cu₁₀Fe₉Cr₁₀ and Al₃Mg₂ materials were tested in a phosphate buffer solution pH 7 at 25 °C to compare their depassivation and subsequent repassivation behaviour. The Al₃Mg₂ material was also tested in a 0.1 M KOH solution pH 13 and 25 °C to reveal the role of constituting metallic elements on the surface film formation. The effect of film formation and removal on the coefficient of friction recorded during unidirectional sliding is discussed.     

Electric and dielectric properties of MgGd0.1Fe1.9O4 ferrite

MgGd_0.1Fe_1.9O₄ ferrite with improved electrical and dielectric properties has been synthesized by conventional ceramic technique. X-ray analysis confirmed the single-phase inverse spinel structure of the ferrite. The dc resistivity is increased by one order of magnitude as compared to Magnesium ferrite. The dielectric loss of the sample investigated at room temperature is only 3 × 10⁻³ at 3 MHz. High resistivity and low dielectric loss can be correlated with better compositional stoichiometry, size and nature of the additives. The variation of dielectric properties of the sample as a function of frequency in the range 0.1–20 MHz has been studied at different temperatures. In addition to this, the electric and dielectric properties have been studied as a function of temperature. Possible mechanisms contributing to the results have been discussed minutely in this paper.     

Kinetics and thermodynamics of hydrogen absorption in the Zr(Al0.1Fe0.9)2 intermetallic compound

Thermodynamic and kinetic characteristics of hydrogen absorption in Zr(Al_0.1Fe_0.9)₂ were investigated at pressures up to 80 atm of H₂ and temperatures between 248 K and 270 K. The heat and entropy of formation of the Zr(Al_0.1Fe_0.9)₂ hydride are estimated to be −24.7 kJ/(mole H₂) and −120 J/(K^*mole H₂), respectively. Small, well-defined samples were utilized for the kinetic research. The experimental kinetic data fit a shrinking core (sc) model, in accord with a visual examination of partly hydrided samples. The pressure dependence of the rate constants indicates an interface-controlled phase transition as the hydride formation rate-determining step. The activation energy for the hydriding process is estimated from Arrhenius plots of the reaction rates to be 0.30 eV/H atom. The kinetic data are discussed in view of similar results for additional intermetallic compounds.     

Influence of ultrasonication on the mechanical properties of Cu/Al2O3 nanocomposite thin films during electrocodeposition

To overcome the poor mechanical properties of pure Cu thin films, we performed electrocodeposition to make nanocomposite thin films by incorporating inert Al₂O₃ nanoparticles (50 nm and 300 nm in diameter). In addition, to reduce agglomeration due to their high surface energy, we used ultrasonication during the electrocodeposition. In this paper, we examined the effects of the ultrasonication on the mechanical properties of nanocomposite films with different ultrasonic energy density up to 225 W/cm². Ultrasonication during electrocodeposition efficiently reduced the agglomeration of nanoparticles and reduced the grain size of the Cu matrix. Smaller nanoparticles were more efficiently de-agglomerated by ultrasonication, which resulted in more enhanced mechanical properties in the 50 nm Al₂O₃ nanoparticle-enhanced specimens. Although the addition of nanoparticles in the Cu matrices significantly increased the hardness of the specimens, as observed in nanoindentation tests, we did not observe such an increase in tensile tests. Reducing the grain size by ultrasonication seems to be an important parameter in enhancing the overall mechanical properties of nanocomposites. Ultrasonication provided a significant increase in all mechanical properties, including elastic modulus, yield stress, ultimate tensile stress, and elongation, of all controlled Cu films.     

Influence of the C14 Ti35.4V32.3Fe32.3 Laves phase on the hydrogenation properties of the body-centered cubic compound Ti24.5V59.3Fe16.2

Bcc Ti_24.5V_59.3Fe_16.2 alloys containing 10 and 30% of C14 Laves phase inclusions were prepared by induction melting followed by annealing at 1000 °C. X-ray powder diffraction and BSE microscopy confirmed the presence of the C14 Laves phase (average composition Ti_35.4V_32.3Fe_32.3) embedded in the bcc matrix. The two end members of the series, the C14 Laves phase and the bcc Ti_24.5V_59.3Fe_16.2 alloy, have very different hydrogenation behaviors. The C14 Laves phase does not absorb as much hydrogen as does the bcc phase. No equilibrium plateau and little hysteresis between absorption and desorption were observed at 25 °C for the C14 Laves on the PCI curves whereas those of the bcc sample present one equilibrium plateau and significant hysteresis between absorption and desorption. As a result, the absorption capacity and the length of the equilibrium plateau of the multiphase alloys decrease with the C14 Laves phase content. The hydrogenation properties of an as-cast bcc Ti_24.5V_59.3Fe_16.2 sample were also investigated: the kinetics of the first hydrogenation is found to be slower and the plateau pressures higher for the as-cast alloy than for the annealed sample.     

Phase diagram of Ni3V-Co3V pseudobinary system

A phase diagram of Ni₃V-Co₃V pseudobinary system is proposed based on x-ray diffraction and differential thermal analysis. Four invariant reactions are located in the phase diagram—two eutectoid and two peritectoid reactions. Six kinds of geometrically close-packed phases are encountered. The stability of these close-packed phases correlate well with the electron concentration.