The formation, structure and properties of nanocrystalline Ni-Mo-B alloys

The structure, structure evolution and microhardness of nanocrystalline Ni-Mo-B alloys were studied by X-ray diffraction, differential scanning calorimetry, transmission and high resolution electron microscopy and microhardness measurements. The nanocrystalline structure was produced by controlled crystallization of amorphous alloys. The annealed samples consist of the FCC nanocrystals with the amorphous regions between them. The grain size of the nanocrystals is about 20 nm and depends on the chemical composition of the alloy. The chemical composition of the amorphous phase between the nanocrystals changes at the annealing. A slight grain growth was observed when the annealing time increases. The diffusion of Mo and B from FCC to the amorphous phase occurs at the annealing. It results in the lattice parameter change. The microhardness of the alloys increases during the annealing. The microhardness values are the same in all alloys before the nanocrystalline structure decomposition. The microhardness is inconsistent with the Petch-Hall equation. The microhardness of the alloys is determined by the microhardness of the amorphous phase bands located between the nanocrystalline grains.     

Formation of nanocrystalline structure during electron irradiation induced crystallization in amorphous Fe-Zr-B alloys

Effect of electron irradiation on the crystallization and phase stability of Fe₈₈Zr₉B₃ and Fe₇₁Zr₉B₂₀ amorphous alloys was examined. Electron irradiation at an accelerated voltage of 2000 kV was performed at room temperature. The Fe₇₁Zr₉B₂₀ alloy showed a wide supercooled liquid region and the ΔT_x value was 71 K, while no glass transition was observed in Fe₈₈Zr₉B₃ alloy. The amorphous phase in Fe–Zr–B alloys was not stable under irradiation and crystallization from the amorphous phase was accelerated by the irradiation. Nanocrystalline structure composed of α-Fe and cubic-Fe₂Zr was formed in Fe₈₈Zr₉B₃ alloy by irradiation induced crystallization, while no nanoscale precipitates of intermetallic compounds were formed during annealing. In Fe₇₁Zr₉B₂₀ alloy, the formation of nanocrystalline precipitates was also confirmed by irradiation induced crystallization, although the formation of nanocrystalline structure had not been realized in high B concentration Fe–Zr–B alloys by annealing. These new results show that electron irradiation is effective in producing a new nanocrystalline structure.     

Physical properties of some iron based alloys in liquid and amorphous states

The atomic structure and the physical properties of amorphous ribbons depend strongly on the state of the melt before quench. It is known that slightly above liquidus metallic melts can preserve a non-equilibrium metastable state for a long time. Moreover some structural transformations in liquid metallic alloys, similar to phase transitions in solids, may take place with an increase of the temperature. In this paper we report measurements of the viscosity, magnetic susceptibility and surface tension in some Fe-based melts. Amorphous ribbons of the same alloys were prepared by standard planar method from different states of the melt. The electrical resistivity, the kinetics of crystallization and the magnetic properties of the ribbons were investigated. It was found that the properties depending upon nanoscale inhomogeneities are different for ribbons produced after different heat treatments of the melt before quench.     

Electronic states in amorphous and crystalline Pd-Ge alloys

Quantitative analysis of carbon in thin films of platinum prepared by d.c. reactive sputtering in argon containing a low percentage of methane was achieved using the ¹²C(d,p₀)¹³C nuclear reaction. The results are compared with those obtained by X-ray microprobe analysis.     

Optical properties of polycrystalline and amorphous cordierite

Cathodoluminescence and infrared absorption studies were made on polycrystalline as well as amorphous cordierite, either in the as-received state or after different thermal treatments. Emission bands centred at about 400 nm were observed in all the samples studied. Red emission bands around 650 nm were also found in samples irradiated with ionizing radiation or annealed in different atmospheres. Infrared absorption measurements were performed to estimate the glass phase and to monitor the presence of OH^– ions.     

Corrosion behaviors of amorphous and nanocrystalline Fe-based alloys in NaCl solution

Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was prepared by the chill block melt-spinning process and nanocrystalline Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was obtained by annealing. The crystallization behaviors were analysed by DSC, XRD and TEM. The electrochemical corrosion behaviors in different annealed states were performed by linear polarization method and electrochemical impedance spectroscopy in 3.5% NaCl solution. The results show that the crystallization of amorphous alloy occurs in the two steps. Some nanometer crystals appear when annealing in 550 degrees C and 600 degrees C, respectively with grain size 13 nm and 15 nm. The nanocrystalline alloy has a tendency to passivation and lower anodic current density than amorphous alloy. It indicates that nanocrystalline alloy has a higher corrosion resistance. Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy consisted of only single semi-circle. When the alloy was annealed in 600 degrees C, its EIS consisted of two time constants, i.e., high frequency and low frequency capacitive loops. The charge transfer reaction resistances increases as annealing temperature rises.     

High-strength Zr-based bulk amorphous alloys containing nanocrystalline and nanoquasicrystalline particles

Abstract

It was recently found that the addition of special elements leading to the deviation from the three empirical rules for the achievement of high glass-forming ability causes new mixed structures consisting of the amorphous phase containing nanoscale compound or quasicrystal particles in Zr–Al–Ni–Cu–M (M ? Ag, Pd, Au, Pt or Nb) bulk alloys prepared by the copper mold casting and squeeze casting methods. In addition, the mechanical strength and ductility of the nonequilibrium phase bulk alloys are significantly improved by the formation of the nanostructures as compared with the corresponding amorphous single phase alloys. The composition ranges, formation factors, preparation processes, unique microstructures and improved mechanical properties of the nanocrystalline and nanoquasicrystalline Zr-based bulk alloys are reviewed on the basis of our recent results reported over the last two years. The success of synthesizing the novel nonequilibrium, high-strength bulk alloys with good mechanical properties is significant for the future progress of basic science and engineering. © 2000 Published by Elsevier Science Ltd.     

FeCuNbSiBV非晶纳米晶合金带材压磁特性研究

研究了Fe71.5Cu1Nb3Si13.5B9V2非晶带材经不同退火工艺处理后的压磁特性,并对不同成分带材的压磁特性进行了对比分析。研究表明,在测试频率f=1 kHz、压应力σ≤0.2 MPa条件下,Fe71.5Cu1Nb3Si13.5B9V2非晶带材闭合回路的电感值随压应力的增大而增大,带材具有良好的压磁稳定性,当退火温度为550℃时,带材的压磁特性稳定性最好,电感值与加载时间、SI(%)与压应力均具有良好的线性关系;热处理工艺对Fe71.5Cu1Nb3Si13.5B9V2带材的压磁性能具有显著影响,退火工艺为300℃×30 min时SI(%)达到最大值0.183;带材的压磁效应与其成分有关,相同测试条件下,Fe73.5Cu1Nb3Si13.5B9带材具有最大的压磁效应,Fe78Si9B13带材次之,Fe71.5Cu1Nb3Si13.5B9V2带材压磁效应最小。     

Comparison of microstructures and tensile properties of pulse electrodeposited Ni on polycrystalline and amorphous substrates

Abstract

Ultrafine grained nickel (UFG Ni) and microcrystalline nickel (MC Ni) were fabricated on two types of substrates, i.e. the amorphous (Ni–P) and polycrystalline (stainless steel) substrates by pulse electrodeposition without additives. This study demonstrates that when inhibiting the epitaxial growth by first depositing a thin amorphous layer on the polycrystalline substrates, the grain size of the subsequent Ni deposit decreases dramatically from microscale to the UFG regime, which depends on the deposition conditions. Compared with MC Ni, which has an ultimate tensile strength σ_UTS of 397 MPa and an elongation to failure ε_TEF of 11·98%, UFG Ni with an average grain size of 120·72 nm exhibits an enhanced σ_UTS of 807 MPa and a comparable ε_TEF of 10·44%. The electrodeposited method used in this study provides an effective and low cost way to produce UFG materials with both high strength and ductility, which can meet the demands for practical application as structural materials.     

Preparation and properties of Fe-B-Si-C amorphous alloys

The crystallization temperatures, magnetic properties, and density of amorphous alloys of FexBySizCzare reported for72 < x < 88, 16 < y < 28, and0 < 2z < 12. The peak value of 4 ± Msis 17 kG in the as-cast state and occurs in the region of Fe82B13Si2.5C2.5. The crystallization temperatures, Curie temperatures, saturation magnetization, and density all appear to be average values of the ternary Fe-B-Si and Fe-B-C properties.     

Microstructure and soft-magnetic properties of FeCoPCCu nanocrystalline alloys

Fe_83.2-xCo_xP₁₀C₆Cu_0.8 (x = 0, 4, 6, 8 and 10) alloys with a high amorphous-forming ability and good soft-magnetic properties were successfully synthesized. Saturation magnetic flux density (B_s) is effectively enhanced from 1.53 T to 1.61 T for as-quenched alloy by minor Co addition, which is consistent well with the result of the linear relationship between average magnetic moment and magnetic valence. For Co-contained alloys, the value of corecivity (H_c) is mainly determined by magneto-crystalline anisotropy, while effective permeability (μ_e) is dominated by grain size and average saturation polarization. After proper heat treatment, the Fe_79.2Co₄P₁₀C₆Cu_0.8 nanocrystalline alloy exhibited excellent soft-magnetic properties including a high B_s of 1.8 T, a low H_c of 6.6 A/m and a high μ_e of 15,510, which is closely related to the high volume fraction of α-(Fe, Co) grains and refined uniform nanocrystalline microstructure.     

Formation and magnetic properties of Fe-B-Si amorphous alloys

The magnetic properties and crystallization temperatures of alloys in the ternary Fe-B-Si system are reported. The Curie temperature increases slightly on replacement of boron by silicon. This results in a sharp ridge of relatively constant room-temperature saturation magnetization extending from Fe80B20to Fe82B12Si6. The coercivity exhibits a broad minimum, both before and after stress relief annealing, in the region around Fe81B15Si4and extending at least to Fe77B13Si10. The crystallization temperature increases with increasing silicon and with decreasing iron and boron. The alloys with silicon are generally easier to prepare in the amorphous state than the binary Fe-B alloys. Thus for the highest saturation magnetization alloy combined with ease of preparation, stability, and lowest losses, the alloys between Fe81B17Si2and Fe82B12Si6are preferred.     

Superconducting properties of amorphous Zr-Ge binary alloys

A new type of refractory metal-metalloid amorphous alloys exhibiting superconductivity has been found in a binary Zr-Ge system by a modified melt-spinning technique. Specimens are in the form of continuous ribbons 1 to 2 mm wide and 0.02 to 0.03 mm thick. The germanium content in the amorphous alloys is limited to the range of 13 to 21 at%. These amorphous alloys are so ductile that no cracks are observed even after closely contacted bending test. The Vickers hardness and crystallization temperature increase from 435 to 530 DPN and from 628 to 707 K, respectively, with germanium content, and the tensile fracture strength is about 1460 MPa. Furthermore, the amorphous alloys exhibit a superconducting transition which occurs very sharply. The superconducting transition temperature (T _c) increases with decreasing germanium content and reaches a maximum value of 2.88 K for Zr₈₇Ge₁₃. The upper critical magnetic field for Zr₈₇Ge₁₃ alloy was of the order of 21.8 kOe at 2.0 K and the critical current density for Zr₈₅Ge₁₅ alloy was about 175 A cm^–2 at 1.70 K in the absence of an applied field. The upper critical field gradient atT _c and the electrical resistivity at 4.2 K increase significantly from 24.6 to 31.5 kOe K^–1 and from 235 to 310cm, respectively, with the amount of germanium. The Ginzburg-Landau (GL) parameter and the GL coherence length §_GL (0) were estimated to be 72 to 111 and about 7.9 nm, respectively, from these experimental values by using the Ginzburg-Landau-Abrikosov-Gorkov (GLAG) theory and hence it is concluded that the Zr-Ge amorphous alloys are extremely soft type-II superconductor with high degree of dirtiness which possesses theT _c values higher than zirconium metal, in addition to high strength combined with good ductility.     

Comparison of the structure and properties of equiatomic and non-equiatomic multicomponent alloys

A series of equiatomic and non-equiatomic Fex(NiCrCo)_100?x (at.-%, x?=?25, 45, 55, 65, 75 and 85) multicomponent alloys were prepared and studied. With the increase in x, the phase structure of the alloys evolves from a single FCC phase (x?=?25, 45 and 55), to a mixture of FCC and BCC phases (x?=?55) and finally to a single BCC phase (x?=?65 and 75). As a result, the BCC-structured alloys have much higher strength and hardness than the FCC-structured alloys. The existing VEC criteria are unable to predict the FCC-BCC phase transition in these alloys.     

Effect of milling time on the structure,micro-hardness,and thermal behavior of amorphous/nanocrystalline TiNiCu shape memory alloys developed by mechanical alloying

In the present paper, the effect of milling process on the chemical composition, structure, microhardness, and thermal behavior of Ti–41Ni–9Cu compounds developed by mechanical alloying was evaluated. The structural characteristic of the alloyed powders was evaluated by X-ray diffraction (XRD). The chemical composition homogeneity and the powder morphology and size were studied by scanning electron microscopy coupled with electron dispersive X-ray spectroscopy. Moreover, the Vickers micro-indentation hardness of the powders milled for different milling times was determined. Finally, the thermal behavior of the as-milled powders was studied by differential scanning calorimetery. According to the results, at the initial stages of milling (typically 0–12 h), the structure consisted of a Ni solid solution and amorphous phase, and by the milling evolution, nanocrystalline martensite (B19′) and austenite (B2) phases were initially formed from the initial materials and then from the amorphous phase. It was found that by the milling development, the composition uniformity is increased, the inter-layer thickness is reduced, and the powders microhardness is initially increased, then reduced, and afterward re-increased. It was also realized that the thermal behavior of the alloyed powders and the structure of heat treated samples is considerably affected by the milling time.     

Deformation properties of amorphous alloys based on titanium

Translated from Fiziko-khimicehskay Mekhanika Materialov, Vol. 27, No. 3, pp. 77–79, May–June, 1991.