Production and mechanical properties of metallic glass-reinforced Al-based metal matrix composites

Al-based metal matrix composites were synthesized through powder metallurgy methods by hot extrusion of elemental Al powder blended with different amounts of metallic glass reinforcements. The glass reinforcement was produced by controlled milling of melt-spun Al₈₅Y₈Ni₅Co₂ glassy ribbons. The composite powders were consolidated into highly dense bulk specimens at temperatures within the supercooled liquid region. The mechanical properties of pure Al are improved by the addition of the glass reinforcements. The maximum stress increases from 155 MPa for pure Al to 255 and 295 MPa for the samples with 30 and 50 vol.% of glassy phase, respectively. The composites display appreciable ductility with a strain at maximum stress ranging between 7% and 10%. The mechanical properties of the glass-reinforced composites can be modeled by using the iso-stress Reuss model, which allows the prediction of the mechanical properties of a composite from the volume-weighted averages of the components properties.     

Formation of quasicrystals in ball-milled amorphous Zr-Ti-Nb-Cu-Ni-Al alloys with different Nb content

In order to investigate the effect of the preparation technique on quasicrystal formation, amorphous (Zr_0.585Ti_0.082Cu_0.142Ni_0.114Al_0.077)_100?x Nb _x alloys with x = 2.5 and 5 at.% were produced by melt spinning and by ball milling of crystalline intermetallic compounds. The calorimetric and microstructure investigations revealed striking similarities between the differently synthesized samples. All the samples are characterized by a two-step crystallization process in which the first crystallization product does not depend on the way of preparation. In fact, the same metastable nanoscale quasicrystalline phase has been obtained by partial devitrification of ball-milled powders as well as of melt-spun ribbons. This demonstrates that ball milling is an alternative processing route to rapid solidification techniques for the preparation of quasicrystal-forming Zr-based alloys.     

Comparative study on sintering behavior of Al86Ni6Y4.5Co2La1.5 mechanically alloyed amorphous powder and melt-spun ribbon

In this research work, the sintering characteristics of Al₈₆Ni₆Y_4.5Co₂La_1.5 mechanically alloyed amorphous powders and milled melt spun ribbon have been compared. Mechanically alloyed amorphous powders were synthesized via 200?h high energy ball milling. Melt spun ribbons were synthesized by single roller melt spinning technique and grounded to powder form by ball milling. Mechanically induced partial crystallization occurred in the ribbons during milling. Significantly higher amount of contaminations such as carbon, oxygen and iron were observed in the mechanically alloyed amorphous powders compared to the milled ribbons. Both powders were consolidated via spark plasma sintering. Superior particle bonding was found in the sample consolidated from milled ribbons, ascribed to the lower amount of contamination that could not effectively restrict the viscous flow and diffusion of atoms. Various complex crystalline phases evolved in the sample consolidated from milled ribbon particles due to the presence of crystalline phases in the powders which acted as nucleation sites, whereas the amorphous phase was mostly retained in its counterpart. Vickers microhardness of the consolidated alloys from milled ribbon and mechanically alloyed amorphous powders were 3.60?±?0.13?GPa and 2.53?±?0.09?GPa, respectively. The higher hardness in the former case was attributed to the superior particle bonding and distribution of hard intermetallic phases in the amorphous matrix.     

Powder metallurgy of Al-based composites reinforced with Fe-based glassy particles: Effect of microstructural modification

Al metal matrix composites reinforced with high volume fraction of Fe_50.1Co_35.1Nb_7.7B_4.3Si_2.8 glassy particles were fabricated by mechanical milling followed by hot pressing. Elemental Al powders blended with 60 vol.% of glassy particles were mechanically milled for 1, 5, 10, 15, and 20?h, respectively. Selected samples were sintered by uniaxial hot pressing under Ar atmosphere. The changes in the microstructure along with their mechanical properties were investigated. Structural and microstructural characterization followed by microhardness and compression test results of the bulk composite material is reported. The use of high volume fraction of Fe-based glassy particles as reinforcement led to significant hardening of the Al matrix while leading to a remarkable combination of high strength and plasticity.     

High formability of glass plus fcc-Al phases in rapidly solidified Al-based multicomponent alloy

A multicomponent Al₈₄Y₉Ni₄Co_1.5Fe_0.5Pd₁ alloy was found to keep a mixed glassy + Al phases in the relatively large ribbon thickness range up to about 200 μm for the melt-spun ribbon and in the diameter range up to about 1100 μm for the wedge-shaped cone rod prepared by injection copper mold casting. The glassy phase in the Al-based alloy has a unique crystallization process of glass transition, followed by supercooled liquid region, fcc-Al + glass, and then Al + Al₃Y + Al₉ (Co, Fe)₂ + unknown phase. It is also noticed that the primary precipitation phase from supercooled liquid is composed of an Al phase instead of coexistent Al + compound phases, being different from the crystallization mode from supercooled liquid for ordinary Al-based glassy alloys. In addition, it is noticed that the mixed Al and glassy phases are extended in a wide heating temperature range of 588–703 K, which is favorable for the development of high-strength nanostructure Al-based bulk alloys obtained by warm extrusion of mixed Al + amorphous phases. The Vickers hardness is about 415 for the glassy phase and increases significantly to about 580 for the mixed Al and glassy phases. The knowledge of forming Al + glassy phases with high hardness in the wide solidification and annealing conditions through high stability up to complete crystallization for the multicomponent alloy is promising for future development of a high-strength Al-based bulk alloy.     

Aluminium based composites strengthened with metallic amorphous phase or ceramic (Al2O3) particles

Two methods were used to obtain amorphous aluminium alloy powder: gas atomization and melt spinning. The sprayed powder contained only a small amount of the amorphous phase and therefore bulk composites were prepared by hot pressing of aluminium powder with the 10% addition of ball milled melt spun ribbons of the Al₈₄Ni₆V₅Zr₅ alloy (numbers indicate at.%). The properties were compared with those of a composite containing a 10% addition of Al₂O₃ ceramic particles. Additionally, a composite based on 2618A Al alloy was prepared with the addition of the Al₈₄Ni₆V₅Zr₅ powder from the ribbons used as the strengthening phase. X-ray studies confirmed the presence of the amorphous phase with a small amount of aluminium solid solution in the melt spun ribbons. Differential Scanning Calorimetry (DSC) studies showed the start of the crystallization process of the amorphous ribbons at 437 °C. The composite samples were obtained in the process of uniaxial hot pressing in a vacuum at 380 °C, below the crystallization temperature of the amorphous phase. A uniform distribution of both metallic and ceramic strengthening phases was observed in the composites. The hardness of all the prepared composites was comparable and amounted to approximately 50 HV for those with the Al matrix and 120 HV for the ones with the 2618A alloy matrix. The composites showed a higher yield stress than the hot pressed aluminium or 2618A alloy. Scanning Electron Microscopy (SEM) studies after compression tests revealed that the propagation of cracks in the composites strengthened with the amorphous phase shows a different character than these with ceramic particles. In the composite strengthened with the Al₂O₃ particles cracks have the tendency to propagate at the interfaces of Al/ceramic particles more often than at the amorphous/Al interfaces.     

Fabrication of bulk amorphous Fe67Co9.5Nd3Dy0.5B20 alloy by hot extrusion of ribbon and study of the magnetic properties

We report on the preparation of bulk amorphous Fe₆₇Co_9.5Nd₃Dy_0.5B₂₀ by hot extrusion of melt-spun ribbons. X-ray diffraction studies were performed to check the structure of the as-spun ribbons and the consolidated bulk specimens. Differential scanning calorimetry (DSC) analysis of the amorphous ribbons revealed that crystallization proceeds in two stages. The first crystallization step leads to the formation of soft magnetic α-(FeCo) and (FeCo)₃B and the second crystallization step corresponds to the formation of the hard magnetic (NdDy)₂(FeCo)₁₄B phase. The hysteresis loop of the as-spun ribbon reveals soft magnetic properties which change to hard magnetic behavior with enhanced remanence after annealing at 973 K for 7 min. X-ray diffraction analysis proves the presence of both soft and hard magnetic phases in the annealed sample. The viscosity of the powder obtained from crushed ribbons was investigated by parallel plate rheometry, showing a distinct viscosity drop in the supercooled liquid region that allows for easy consolidation of the crushed ribbons. The hot extruded sample that was subsequently annealed at 973 K for 7 min exhibits good hard magnetic properties with coercivity H_c = 218 kA/m, saturation magnetization J_s = 1.36 T, maximum energy product (BH)_max = 91.3 kJ/m³ and remanence B_r = 1.18 T (after demagnetization field correction), respectively.     

Ball milling of Co70 Fe8Si9B13 amorphous ribbon,crystallized ribbon and a mixture of pure crystalline powders

Co₇₀ Fe₈ Si₉B₁₃ amorphous ribbon, crystallized ribbon and a mixture of pure crystalline powders were mechanically alloyed by milling and nanocrystalline structures were obtained. The structural changes were monitored By X-ray diffraction and differential scanning calorimetry measurements. The thermal behaviour on heating the alloys prepared by ball milling was studied and the influence of the high-energy ball milling on the resulting phases was found.     

Transformation behavior and thermal stability of Al-based systems prepared by ball milling

Transmission electron microscopy, X-ray diffraction, scanning electron microscopy, differential thermal analysis, and differential scanning calorimetry were used to investigate the transformation behavior of (Al_0.88Ni_0.08Co_0.04)_100−x,Zr_x, (wherex = 0 to 5 at. %) alloys during ball milling, and the thermal stability during the reverse process of return to equilibrium. The results have shown that the crystalline to amorphous transformation occurs only in compositions containing Zr. Mechanical grinding is shown to easily amorphize the Al₃Zr compound which enters in equilibrium with the fcc-Al and (Co, Ni)₂Al₉ phases for the compositions studied. The formation of an amorphous phase at the fcc-Al and Co₂Al₉ grain boundaries leads to a wetting transition, and with decreasing grain size the initially nanostructured Al₈₈Ni₈Co₄ alloy was found to progressively transform to an amorphous alloy. The crystallization temperature, the activation energy, and the crystallization enthalpy increase, while the melting temperature of the quaternary alloys decrease with increasing Zr substitution up to 5 at. %.     

Reactive hot pressing of Al2O3-Ni composites

Reactive hot pressing has been used to form Al₂O₃-Ni composites from Al and NiO. The effect of attrition milling on the precursor powder and subsequent composite formation was examined. The surface area, phase assemblage, reaction temperature, and morphology of precursor powders were characterized as a function of milling time, which ranged from 0 (unmilled) to 480 min (8 hrs). During milling, particle surface area increased from less than 1 to more than 11 m²/g as the size of the Al and NiO particles decreased. At the same time, the temperature at which Al and NiO reacted to form Al₂O₃ and Ni decreased from more than 1000°C to around 600°C. Formation of Al₂O₃ or Ni during milling was not detected, regardless of time. Precursor milling time also affected the morphology and phase assemblage of composites produced by reactive hot pressing. Composites formed from unmilled powders contained a small amount of unreacted NiO and had a Ni ligament size greater than 10 m. The composite forming reaction went to completion when powders milled for one hour or more were hot pressed. Based on microstructural evidence and analogy to similar reactions, it appears that the composite forming reaction proceeds by Al diffusing into and reacting with NiO.     

Pulvermetallurgische Erzeugung von SiC‐ und Al2O3‐verstärkten Al‐Cu‐Legierungen

Powder metallurgical fabrication of SiC and Al₂O₃ reinforced Al‐Cu alloys Based on metallographic studies the states of composite powder formation during high‐energy ball milling will be discussed. Spherical powder of aluminium alloy AA2017 was used as feedstock material for the matrix. SiC and Al₂O₃ powders of submicron and micron grain size (<2 μm) were chosen as reinforcement particles with contents of 5 and 15 vol.‐% respectively. The milling duration amounted to a maximum of 4 hours. The abrasion of the surface of the steel balls, the rotor and the vessel is indicated by the content of ferrous particles in the powder. High‐energy ball milling leads to satisfying particle dispersion for both types of reinforcement particles. Further improvements are intended. The microstructure of compact material obtained by hot isostatic pressing and extrusion was studied in detail by scanning and transmission electron microscopy. For both types of reinforcement the microstructure of composites is similar. The microporosity is low. The interface between reinforcement particles and matrix is free of brittle phases and microcracks. In the case of SiC reinforcement particles, a small interface interaction is detectable which implies a good embedding of reinforcement particles. High‐energy ball milling under air‐atmosphere leads to the formation of the spinel phase MgAl₂O₄ during the subsequent powder‐metallurgical processing. Because of the size, rate and dispersion of the spinel particles, an additional reinforcement effect is expected.     

Effect of Ni addition on formation of amorphous and nanocrystalline phase during mechanical alloying of Al-25 at.%Fe-(5,10) at.%Ni powders

Al-Fe-Ni ternary powder mixtures containing 25 at.%Fe-5 at.%Ni and 25 at.%Fe-10 at.%Ni were mechanically alloyed by a high-energy planetary ball mill. Structural evolution of these powders during milling was investigated by X-ray diffraction technique and transmission electron microscopy. Almost complete amorphous phase in Al₇₀Fe₂₅Ni₅ system is observed at the early milling stage. The amorphous phase transforms into metallic compound Al₅(Fe,Ni)₂ and then the compound changes to ordered Al(Fe,Ni) phase. The last milling products in Al₇₀Fe₂₅Ni₅ system are amorphous phase plus nanocrystalline of the disordered Al(Fe,Ni) phase changed from the ordered Al(Fe,Ni) phase. During milling of Al₆₅Fe₂₅Ni₁₀ system, α-Al and α-Fe solid solutions formed at the early stage change to the ordered Al(Fe,Ni) compound and at last the ordered phase changes to the disordered Al(Fe,Ni) phase. Ten percent of Ni addition promotes retardation of the formation of the amorphous phase.     

Synthesis of LaB<Subscript>6</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powders via ball milling-assisted annealing

In this study, LaB₆–Al₂O₃ nanocomposite powders were synthesized via ball milling-assisted annealing process starting from La₂O₃–B₂O₃–Al powder blends. High-energy ball milling was conducted at various durations (0, 3, 6 and 9 h). Then, the milled powders were annealed at 1200 °C for 3 h under Ar atmosphere in order to obtain LaB₆ and Al₂O₃ phases as reaction products. X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) and transmission electron microscopy (TEM) techniques were utilized to carry out microstructural characterization of the powders. No reaction between the reactants was observed in the XRD patterns of the milled powders, indicating that high-energy ball milling did not trigger any chemical reactions even after milling for 9 h. LaAlO₃ and LaBO₃ phases existed in the annealed powders which were milled for 0, 3 and 6 h. LaBO₃ phase was removed after HCl leaching. 9-h milled and annealed powders did not exhibit any undesired phases such as LaAlO₃ and LaBO₃ after leaching step, and pure nanocrystalline LaB₆–Al₂O₃ composite powders were successfully obtained. TEM analyses revealed that very fine LaB₆ particles (~?100 nm) were embedded in coarse Al₂O₃ (~?500 nm) particles.     

Mechanically induced self-propagating reaction and consequent consolidation for the production of fully dense nanocrystalline Ti55C45 bulk material

We employed a high-energy ball mill for the synthesis of nanograined Ti₅₅C₄₅ powders starting from elemental Ti and C powders. The mechanically induced self-propagating reaction that occurred between the reactant materials was monitored via a gas atmosphere gas-temperature-monitoring system. A single phase of NaCl-type TiC was obtained after 5 h of ball milling. To decrease the powder and grain sizes, the material was subjected to further ball milling time. The powders obtained after 200 h of milling possessed spherical-like morphology with average particle and grain sizes of 45 μm and 4.2 nm, respectively. The end-products obtained after 200 h of ball milling time, were then consolidated into full dense compacts, using hot pressing and spark plasma sintering at 1500 and 34.5 MPa, with heating rates of 20 °C/min and 500 °C/min, respectively. Whereas hot pressing of the powders led to severe grain growth (~ 436 nm in diameter), the as-spark plasma sintered powders maintained their nanograined characteristics (~ 28 nm in diameter). The as-synthesized and as-consolidated powders were characterized, using X-ray diffraction, high-resolution electron microscopy, and scanning electron microscopy. The mechanical properties of the consolidated samples obtained via the hot pressing and spark plasma sintering techniques were characterized, using Vickers microhardness and non-destructive testing techniques. The Vickers hardness, Young's modulus, shear modulus and fracture toughness of as-spark plasma sintered samples were 32 GPa, 358 GPa, 151 GPa and 6.4 MPa·m^1/2, respectively. The effects of the consolidation approach on the grain size and mechanical properties were investigated and are discussed.     

Structural,Thermal and Magnetic Properties of Nanocrystalline Co<Subscript>80</Subscript>Ni<Subscript>20</Subscript> Alloy Prepared by Mechanical Alloying

Co₈₀Ni₂₀ powder mixture was mechanically alloyed by high-energy planetary ball milling, starting from elemental Co and Ni metal powders. The morphological, microstructural, thermal and magnetic properties of the milled powders were characterised respectively by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and vibratory sample magnetometry. In addition to a highly disordered phase, two face-centred cubic (FCC) and hexagonal close-packed (HCP), solid solutions, FCC Co(Ni), FCC Ni(Co) and HCP Co(Ni), are observed after 3 h of milling. Their grain sizes decrease with increase in milling time attaining, at 48 h of milling, 12 nm, 25 nm and 10 nm, respectively. Beyond a certain milling time, no further refinement of the microstructure occurs and the morphological equilibrium is usually given by a bimodal particle size distribution. Magnetic measurements of the milled Co₈₀Ni₂₀ alloy powder exhibit a soft ferromagnetic character where the magnetic parameters are sensitive to the milling time mainly due to the particle size refinement as well as the formation of Co(Ni) and Ni(Co) solid solutions. Both the saturation magnetisation ( M _s) and coercivity ( H _c) were found to decrease with milling time, attaining the values of M _s = 126 emu/g and H _c = 60 Oe after 48 h of milling.     

Crystallization kinetics of Zr60Al15Ni25 bulk glassy alloy

The crystallization kinetics of Zr₆₀Al₁₅Ni₂₅ bulk glassy alloy under isochronal and isothermal conditions has been investigated by differential scanning calorimetry (DSC). The microstructure of as-cast Zr₆₀Al₁₅Ni₂₅ bulk glassy alloy is observed by high-resolution electron microscopy (HREM). It is found that there exist nanocrystals with a size of about 7 nm in the glassy matrix, which are not observed in the XRD image. The results of Kissinger analysis show that the effective activation energies for glass transition (457 kJ/mol) and crystallization (345 kJ/mol) are high, indicating that it has large thermal stability against crystallization. The crystallization of Zr₆₀Al₁₅Ni₂₅ bulk glassy alloy under isothermal annealing can be modeled by the Johnson-Mehl-Avami equation. The crystallization kinetics parameters show that the isothermal crystallization starts from the growth of the pre-existing nanocrystals and the crystallization process is diffusion-controlled.     

Ultrafast synthesis of the nanostructured Al59Cu25.5Fe12.5B3 quasicrystalline and crystalline phases by high-energy ball milling: Microhardness,electrical resistivity,and solar cell absorptance studies

In this study, the Al₅₉Cu_25.5Fe_12.5B₃ nanoquasicrystalline alloy and related crystalline phases were synthesized through mechanical alloying using a high-energy ball milling and consolidated by a cold isostatic pressing apparatus. This paper focuses on the synthesis, structural and microstructural evolutions, thermal stability, microhardness, and electrical and optical properties of the Al₅₉Cu_25.5Fe_12.5B₃ nanoquasicrystalline alloy for solar selective absorber usages. The structural evolutions of the mechanically alloyed and heat-treated AlCuFeB powders were investigated by X-ray diffractometry. Accordingly, the effect of milling time and heat treatment on the formation of quasicrystalline and related crystalline phases were studied in the AlCuFeB alloy system. The microstructure, morphology, and chemical microanalysis of the un-milled and as-milled powders were examined by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The composition of the as-milled AlCuFeB powders was estimated employing inductively coupled plasma-atomic emission spectroscopy. The thermal stability of the AlCuFeB powders was recorded by differential thermal analysis, and the weight gain of the particles during annealing was investigated through thermogravimetric analysis. The nanostructured Al₅₉Cu_25.5Fe_12.5B₃ stable quasicrystalline phase and crystalline Al(Cu,Fe) solid-solution were synthesized by the ultrafast milling procedure in 1 h. The rationale behind using the term ultrafast synthesis is to synthesize the QC i-phase only by the high-energy ball milling procedure in short-term ball milling without subsequent annealing treatment. However, the single quasicrystalline phase could not be obtained even after the annealing treatment. The quasicrystalline size was calculated by the Williamson–Hall method and optimized by the Rietveld refinement procedure, and it was found that the size is varied between 53 and 61 nm. Furthermore, the particle size distribution of the as-milled AlCuFeB powders was measured using laser static light scattering, which ranges from 0.1 to 50 μm. The microhardness of the consolidated as-milled and heat-treated samples was estimated utilizing the Vickers microhardness indenter. At the same time, their electrical resistivity was assessed by the four-point probe method at room temperature. The spectral analyses of absorption on the consolidated as-milled samples were carried out in the ultraviolet, visible, and near-infrared regions. It was found that the presence of the quasicrystalline phase in the AlCuFeB alloy prominently improves the microhardness, electrical resistivity, and particularly sunlight absorptance.     

Improved activation and hydrogen storage properties of a Mg85Ni15 melt-spun alloy via surface treatment with NH4 solution

An amorphous Mg₈₅Ni₁₅ melt-spun hydrogen storage alloy, processed by submersion in an aqueous solution of NH₄⁺, is able to absorb nearly 5 mass% hydrogen at 473 K during the first hydrogenation cycle. The nanocrystalline microstructure formed during devitrification of the metallic glass is preserved by the lower required activation temperature of the NH₄⁺-treated material compared to the as-spun material; and the kinetics of subsequent absorption/desorption cycles at 573 K are dramatically improved. The material activated at 473 K exhibits a decrease in hydride decomposition temperature by 30 K, observed via DSC and TPD experiments, compared to a sample activated at 573 K. The NH₄⁺-treatment of a glassy alloy presented here provides a practical alternative to ball milling for forming a nanocrystalline material and facilitating activation, requiring much less time and a more commercially scalable option.     

Fabrication of bulk Al-La-Ni alloy by spark plasma sintering

The bulk Al₈₅La₁₀Ni₅ alloy is sintered by spark plasma sintering (SPS) method. The microstructure and mechanical properties of the Al₈₅La₁₀Ni₅ samples are investigated. The results show that the bulk Al₈₅La₁₀Ni₅ alloy with less than 1.5% porosity has been obtained at 693 K. The hardness of the alloy sintered at 693 K reaches HRB 98 and the wear resistance of the alloy is twice of the conventional A390 aluminum alloy. The high wear resistance of aluminum alloy is attributed to second-phase strengthening.