Microstructure and properties of the in situ formed amorphous-crystalline composites in the Fe-Cu-based immiscible alloys

The paper presents microstructures and mechanical properties of the melt-spun Fe₃₀Cu₃₂Si₁₃B₉Al₈Ni₆Y₂ and Fe₄₄Cu₁₈Si₁₃B₉Al₈Ni₆Y₂ alloys. It was found that liquid phase separation of the initially homogeneous melt occurred due to a positive heat of mixing between two major elements. The microstructures of the melt-spun ribbons were composed of the Fe-rich amorphous and the Cu-rich crystalline phases. A significant effect of the melt ejection temperature and the chemical composition (Fe and Cu content) on microstructures of rapidly solidified alloys was revealed. The microstructures of ribbons melt-spun from the miscibility gap region were non-uniform. On the other hand the microstructures of ribbons melt-spun from homogeneous melt temperature region were composed of the spherical precipitates distributed within the matrix. Superior hardness values of the examined ribbons melt-spun from the same temperature were found for the alloy with higher iron content. An increase of the melt-ejection temperature in the homogeneous melt region resulted in hardness decrease in case of the Fe₃₀Cu₃₂Si₁₃B₉Al₈Ni₆Y₂ alloy and its increase for the Fe₄₄Cu₁₈Si₁₃B₉Al₈Ni₆Y₂ ribbons.     

The microstructure development in Fe32Cu20Ni28P10Si5B5 immiscible alloy and possibilities of formation of amorphous/crystalline composite

Durch Messungen mittels differentieller Thermal-Analyse und dazu komplementäre Untersuchungen der Mikrostrukturen an Fe-Cu Legierungen ergibt sich erstmals der Nachweis für das Auftreten von kritischer-Punkt Benetzung an einer vollständig metastabilen Mischungslücke. Die damit verbundene vollständige Benetzung tritt in dem Zusammensetzungsbereich von 50–65 at.% Fe nahe der kritischen Konzentration auf. Glaseingelagerte Proben zeigen die vollständige Benetzung des Glases durch die Cu-reiche Schmelze während des Unterkühlens bis zur metastabilen Mischungslücke. Im Zusammensetzungsbereich der vollständigen Benetzung erfolgt die Entmischung bei der zugehörigen Binodaltemperatur ohne zusätzliche Unterkühlung. Bei der Erstarrung der phasenseparierten Schmelze aus tiefer Unterkühlung führt dies zu einem grobskaligen Entmischungsgefüge. Im Gegensatz dazu zeigt die Entmischungsreaktion bei Zusammensetzungen außerhalb des Intervalls vollständiger Benetzung eine merkliche Unterkühlung unterhalb der jeweiligen Binodaltemperatur. Das zugehörige Erstarrungsgefüge zeigt die Phasentrennung auf einer deutlich kleineren Skala. Ohne Glaseinlagerung befinden sich die Proben in Kontakt zu dem Al₂O₃-Tiegel und zu einer Oberflächenschicht aus Eisenoxid. Unter diesen Bedingungen findet kritischer-Punkt Benetzung auf beiden Seiten der kritischen Zusammensetzung statt. Diese Ergebnisse demonstrieren daß kritischer-Punkt Benetzung unabhängig von der Probenumgebung erfolgt, daß jedoch die benetzende Phase oberflächenempfindlich ist und durch die Probenumgebung selektiert wird.

In situ composite formation in the Ni–(Cu)–Ti–Zr–Si system

In situ composites were synthesized by arc melting Ni–(Cu)–Ti–Zr–Si alloys. The X-ray diffraction patterns of rapidly cooled cast strips show a primary Ni(Ti, Zr) B2 structure superimposed on the diffuse scattering maxima from the amorphous phase. Compression test results show that the composite starts to yield at 1200 MPa and fractures at 1900 MPa.     

Reinforcement of Al–Fe–Ni alloys with the in situ formation of composite materials

One of the most effective methods for the improvement of the mechanical properties of metals is their reinforcement with non-metallic materials. In the present work powder of K₂TiF₆ and KBF₄ was added in an Al–Fe–Ni alloy while the alloy was in liquid form at 1060 °C with a 5 wt.% mixture of powders and with simultaneous stirring for 30 min. The liquid was squeeze-casted at 150 bar. The as-cast specimens were examined with electron microscopy and X-ray diffraction. SEM analysis revealed that the as-formed material is composed by needle-like crystallites along with a dentritic form and an interdendritic phase. The composition of the needle-like crystallites may presumably be expressed by the formula (Fe-Ni)Al₃. The rest of the matrix consists of almost pure Al grown dentritically, while the interdendritic phase contains Fe and Ni dissolved in Al. EDS analysis also proved the existence of spots with high Ti concentration, which probably refer to the Ti–B compounds. Finally TEM verified the presence of nanocrystals in the matrix.     

Thermal stability and magnetic properties of Gd–Fe–Al bulk amorphous alloys

Gd₆₅Fe₂₀Al₁₅, Gd₆₅Fe₁₅Al₂₀ and Gd₇₀Fe₁₅Al₁₅ bulk amorphous alloys were produced by copper mold casting method with the maximum diameters of 2, 1 and 1 mm, respectively. The crystallization temperature (T_x) and melting temperature (T_m) of the Gd₆₅Fe₂₀Al₁₅ bulk amorphous alloy are 808 and 943 K, respectively. Accordingly, the temperature interval of T_m and T_x, ΔT_m (=T_m − T_x), is as small as 135 K and the reduced crystallization temperature (T_x/T_m) is as high as 0.86. The small ΔT_m and high T_x/T_m values are presumed to be the origin for the achievement of the high amorphous-forming ability of the Gd–Fe–Al bulk amorphous alloy. The Gd₆₅Fe₂₀Al₁₅, Gd₆₅Fe₁₅Al₂₀ and Gd₇₀Fe₁₅Al₁₅ bulk amorphous cylinders with a diameter of 1 mm exhibit superparamagnetism at room temperature, while the amorphous ribbon shows the paramagnetism at room temperature. Finally, the mechanical properties of Gd₆₅Fe₂₀Al₁₅ bulk amorphous alloys are investigated.     

Local structural fluctuation in Pd–Ni–P bulk metallic glasses examined using nanobeam electron diffraction

Local structural fluctuation in relation to the medium range order (MRO) in a Pd–Ni–P bulk metallic glass was examined using nanobeam electron diffraction (NBED) technique. We found diffraction spots with strong intensities in the NBED patterns taken from any observation sites in the specimen. This indicates a presence of MRO regions densely formed in the specimen. The diffraction spots in NBED were normally dispersed around positions corresponding to the first halo-diffraction ring in selected area diffraction. A low-temperature annealing led to form a nanocrystalline microstructure consisting of unidentified phosphides. In the course of annealing, the MRO structures deduced from the NBED patterns have no structural similarity to the phosphides found in the primary crystallization stage. The MRO structure changes into a similar structure with the primary crystals just before the crystallization. A discussion is made for the MRO structure and its relation to the glass stability and also to the phosphide nucleation in the primary crystallization.     

Formation, properties and microstructure of amorphous/crystalline composite Ag20Cu30Ti50 alloy using miscibility gap

The aim of the work was to produce the amorphous/crystalline composite with uniform distribution of fine crystalline soft phase. Silver–copper–titanium Ag₂₀Cu₃₀Ti₅₀ alloy was prepared using 99.95 wt% Ag, 99.95 wt% Cu, 99.95 wt% Ti that were arc-melted in argon atmosphere. Then the alloy was melt spun on a copper wheel with linear velocity of 33 m/s. Investigation of the microstructure for both arc-melt massive sample and melt-spun ribbons was performed with use of scanning electron microscope (SEM) with EDS, light microscope (LM) and X-ray diffraction. The thermal stability was evaluated by differential scanning calorimetry (DSC). The properties such as Young modulus and Vickers hardness number before and after crystallization of the amorphous matrix were measured with use of nanoindenter. The microstructure was investigated by transmission electron microscope (TEM). It was found, that the alloy has a tendency for separation within the liquid state due to the miscibility gap which resulted in segregation into Ti–Cu–Ag matrix and Ag-base spherical particles after arc-melting. During rapid cooling through the melt spinning the Ag₂₀Cu₃₀Ti₅₀ alloy formed an amorphous/crystalline composite of fcc silver-rich spherical particles within the amorphous Ti–Cu–Ag matrix.     

Characterization of interface between the particles in NiNbZrTiPt metallic glassy matrix composite containing SiC fabricated by spark plasma sintering

We investigated the microstructure, in particular, the interface structure between powder particles in the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 bulk glassy alloy composites containing 10 vol.%SiC particulates prepared by a spark plasma sintering (SPS) process by means of scanning and transmission electron microscopies. The SiC particulates were dispersed homogeneously in the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 glassy matrix. No crystallization of the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 glassy alloy took place during the SPS process. The good bonding states between SiC particulates and glassy matrix, as well as between glassy particles were recognized. No intermediate layer in the bonded interfaces was observed.     

Characterization of an amorphous–crystalline Mg-based composite

An amorphous–crystalline Mg-based composite with the nominal composition of Mg₆₅Cu₂₀Zn₅Y₁₀ has been formed by casting. X-ray diffractometry, differential scanning calorimetry, backscatter electron imaging, and energy dispersive X-ray analysis were used to characterize the structure of the composite, which is linked to the hardness, modulus, and fracture toughness obtained by Vickers and nanoindentation. Comparisons of the structure–property relationships are also made to composite materials of a similar composition. The effects of the crystalline microstructure on localized deformation through shear banding are discussed and related to the hardness and toughness results.     

Structure and crystallization kinetics of a Cu50Zr45Ti5 glassy alloy

The crystallization kinetics and structure changes in a melt-spun Cu₅₀Zr₄₅Ti₅ glassy alloy on heating were investigated by X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and differential isothermal calorimetry. The glassy phase in the Cu₅₀Zr₄₅Ti₅ alloy was crystallized forming Cu₁₀Zr₇ and CuZr₂ phases upon thermal annealing. The activation energy for crystallization obtained by the Arrhenius equation was 435 kJ/mol. The crystallization process took place by nucleation and growth mechanism, and an Avrami exponent of about 3.3 may indicate a three-dimensional interface-controlled growth of nuclei with a decreasing nucleation rate.     

Microstructure and phase transformations in a liquid immiscible Fe60Cu20P10Si5B5 alloy

This work presents a study of the microstructure formed in a liquid immiscible Fe₆₀Cu₂₀P₁₀Si₅B₅ alloy during moderate cooling on a copper plate and melt-spinning. The alloy ingot was re-melted on a copper plate and observed while cooling using a mid-wave infra-red (MWIR) camera. The heating and cooling characteristics of the melt-spun ribbon were studied using differential scanning calorimetry (DSC). The morphology and chemical composition of the ingot as well as the melt-spun ribbon were analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The compositions of the ingot and the ribbon were investigated using X-ray diffraction (XRD). Mössbauer spectroscopic measurements showing the influence of adding Cu to the Fe–Si–P–B alloy were also analyzed.The IR images from the MWIR camera enabled direct observation and identification of the liquid state transformations of the alloy. The DSC trace of the melt-spun ribbon showed crystallization of the amorphous matrix and confirmed that high temperature transformations occurred when the alloy was in the liquid state. Observations of the microstructure of the ingot revealed crystalline surface fractal structures formed by the Fe-rich eutectic constituent and Cu-rich fcc spherical precipitates. The morphology of the precipitates indicated that the precipitates formed in the miscibility gap. The microstructure of the melt-spun ribbon is composed of an amorphous Fe-rich matrix and elongated Cu-rich fcc precipitates. The observations based on the study of the microstructure are supported by Mössbauer spectroscopy.     

Fe-Si-B-Cu体系中原位析出非晶/晶体复合粉末的制备与性能研究

本研究基于相图计算的CALPHAD方法和超音雾化技术,设计并制备了具有典型核/壳结构的(Fe0.75Si0.1B0.15)100-xCux(x=0,30,45,55,65,at%)非晶/晶体复合粉末。实验研究了该系列晶体/非晶复合粉体的显微组织,热稳定性,形成机理和磁性能。结果表明:本研究制备的复合粉体均由分布在核层的富FeSiB非晶相和壳层的富Cu相组成。磁滞回线结果表明,随着Cu含量的增加,饱和磁化强度呈线性关系逐渐降低,但对矫顽力的影响并不明显。该类非晶/晶体复合粉体的形成过程为:(1)高温下富Cu相和富FeSiB相的液相分离现象诱发形成核/壳组织;(2)由于富Cu相的玻璃形成能力远低于富FeSiB相,在超音雾化过程中,富FeSiB相从液态被冻结为非晶态,最终形成具有核/壳结构的非晶/晶体复合粉体。     

Structures and superparamagnetic properties of overaged Fe–Al–Mn–C alloys

Microstructures and superparamagnetic properties in aged-hardened Fe–9%Al–30%Mn– (x)C,Si alloys, resulting from overaging at a temperature of 823 K for 48 h to 313 days, have been investigated by transmission electron microscopy (TEM), X-ray diffraction patterns, and vibrating sample magnetometry (VSM). The results reveal that the precipitate κ-phase [(Fe,Mn)₃AlC] decomposition in this alloy, overaged at 823 K for one week, resulted from two separate mechanisms: (1) wetting of the antiphase boundary segment (APBs) of D0₃ [(Fe/Mn)₃Al] domains by the B2 [(Fe/Mn)Al] phase; and (2) precipitation of the B2 [(Fe/Mn)Al] phase within the domain. A superparamagnetic behaviour was discovered when the alloy was overaged at 823 K for ≈120–313 days. The super-soft magnetic property was mainly attributable to the ferromagnetic spinel-ordered (B2 [(Fe/Mn)Al]+D0₃ [(Fe/Mn)₃Al]) phases and ordered B2 with monoclinic ′Mn structures.     

Tribological behavior of B4C reinforced Fe-base bulk metallic glass composite coating

In the present study, the tribological behavior of B₄C reinforced Fe-based bulk metallic glass (BMG) in the form of spray coatings was investigated. These coatings were successfully deposited on mild steel substrates using shrouded plasma spray techniques. The B₄C fraction and distribution in the deposited BMG/B₄C coatings were evaluated by image analysis and scanning electron microscopy. Friction and wear experiments were performed under dry conditions using a pin-on-disk sliding wear test against SUJ2 countermaterial for different B₄C fractions. It was observed that the wear resistance of composite coatings was greatly improved relative to the BMG coating. The results show that the friction coefficient of BMG/B₄C coatings is dependent on the fraction of B₄C in the BMG matrix. The wear behavior of Fe-based BMG is governed by plastic deformation and fracture of the wear surface. By embedding a harder material, B₄C, in a comparatively soft matrix, the hardness of the wear surface can be increased, and plastic flow propagation is inhibited. Moreover, the lower friction coefficient of B₄C can lead to reductions in wear loss.     

DO22–(Cu,Ni)3Sn intermetallic compound nanolayer formed in Cu/Sn-nanolayer/Ni structures

The present work conducts crystal characterization by High Resolution Transmission Electron Microscopy (HRTEM) on Cu/Sn-nanolayer/Ni sandwich structures associated with the use of Energy Dispersive X-ray (EDX) analysis. The results show that DO₂₂–(Cu,Ni)₃Sn intermetallic compound (IMC) ordered structure is formed in the sandwich structures at the as-electrodeposited state. The formed DO₂₂-(Cu,Ni)₃Sn IMC is a homogeneous layer with a thickness about 10 nm. The DO₂₂–(Cu,Ni)₃Sn IMC nanolayer is stable during annealing at 250 °C for 810 min. The formation and stabilization of the metastable DO₂₂–(Cu,Ni)₃Sn IMC nanolayer are attributed to the less strain energy induced by lattice mismatch between the DO₂₂ IMC and fcc Cu crystals in comparison with that between the equilibrium DO₃ IMC and fcc Cu crystals.     

The effect of roll gap geometry on microstructure in cold-rolled aluminum

Microstructure and texture are analyzed through the thickness of two aluminum plates cold-rolled 40% with different roll gap geometries. It is found that both texture and microstructure are strongly affected by the rolling geometry. After rolling with intermediate-size draughts a rolling-type texture is developed throughout the plate thickness. In this case, grains are subdivided by extended planar dislocation boundaries preferentially aligned at an angle of 40 ± 15° to the rolling direction. In the plate rolled with small draughts, shear texture components appear in the intermediate layers. In these layers, extended planar dislocation boundaries are frequently found to be inclined closely to the rolling direction. The subsurface and central layers of this plate exhibit microstructures similar to those in the plate rolled with intermediate draughts. It is suggested that the development of different textures and microstructures at different depths is related to the activation of different slip systems due to through-thickness strain gradients.     

Effect of amorphous–crystalline interfaces on the martensitic transformation in Ti50Ni25Cu25

A partially crystallized amorphous Ti₅₀Ni₂₅Cu₂₅ melt-spun ribbon showing spherical particles in martensite has been investigated. Microstructural observations support the hindering of the martensitic transformation as well as the production of additional autoaccommodated structures nearby the interface compared with the ones used inwards.     

Effect of manganese on the microstructure of Mg–3Al alloy

The effect of manganese on the microstructure of Mg–3Al alloy, especially the nucleation efficiency of Al–Mn particles on primary Mg, has been investigated in this paper. Mg–0.72Mn was used to fabricate Mg–3Al–xMn (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys, and the grain sizes of these alloys fluctuate at 390 μm indicating addition of manganese does not evidently influence the grain size of Mg–3Al alloy. Through XRD, FESEM and TEM detection, it is found that Al_0.89Mn_1.11 compound is the dominant Al–Mn phase in Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, and distributes in primary Mg matrix and interdendritic regions with an angular blocky morphology. The number of Al_0.89Mn_1.11 increases gradually with increasing manganese content while the grain sizes of primary Mg are nearly the same in Mg–3Al, Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, indicating Al_0.89Mn_1.11 has low nucleation efficiency on primary Mg.