Quasicrystalline phase formation during heat treatment in mechanically alloyed Al65Cu20Fe15 alloy

Abstract

Quasicrystalline phase formation during heat treatment in the mechanically alloyed Al₆₅Cu₂₀Fe₁₅ powders was studied by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The mechanical alloying was performed at speed of 300 rev min^–1 for times up to 70 h. It was found that mechanical alloying of the Al₆₅Cu₂₀Fe₁₅ powders did not result in the quasicrystalline (QC) icosahedral phase (i-phase) formation. The long time milling resulted in the formation of a cubic Al (Cu,Fe) solid solution phase (β-phase). The cubic Al (Cu,Fe) solid solution identified as β-phase was observed to be present as one of the major phases in the Al₆₅Cu₂₀Fe₁₅ alloy. The formation of the quasicrystalline icosahedral phase (i-phase) was only observed for short time milled powders after additional annealing at temperature above 500°C. The present investigation also showed that a tetragonal Al₂Cu phase (θ-phase) forms with short time milling. The tetragonal Al₇Cu₂Fe₁ phase (w-phase) was observed after heat treatment of the short time milled and unmilled powders. The present investigation indicated that an effective process to prepare the quasicrystalline materials was using a combination of short time milling and subsequent annealing.     

Mechanical alloying behavior of Ti6Al4V residual scraps with addition of Al2O3 to produce nanostructured powder

The present investigation has been based on production and subsequent comparison of different physical, mechanical and thermal properties of nanostructured Ti6Al4V and Ti6Al4V/Al₂O₃ powders by means of high energy ball milling. In this regard, the structural and morphological changes of powders were investigated by X-ray diffraction, scanning electron microscopy and microhardness measurements. The results revealed that ball milling process reduced the grain size of Ti6Al4V and Ti6Al4V + 10 wt% Al₂O₃ to approximately 20 and 15 nm, respectively. For both compositions also a remarkable change in morphology and particle size occurred during ball milling of powders with different compositions. Moreover, phase evolution during milling and heat treatment was taken into consideration. The as-milled Ti6Al4V + 10 wt% Al₂O₃ powder exhibited higher microhardness (∼900 Hv) comparing to as-milled Ti6Al4V (∼536 Hv) and as-received samples (∼400 Hv).     

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.     

Structure and mechanical properties of mechanically alloyed Al/Al-Cu-Fe composites

Quasicrystalline (QC) powder was prepared by mechanical alloying and subsequent annealing of Al₆₅Cu₂₃Fe₁₂ composition. Obtained quasicrystals were milled together with pure aluminium in the ratios of Al-20 wt% QC and Al-10 wt% QC. A hot consolidation of samples was performed under pressure of 4.5 GPa at elevated temperatures. X-ray diffraction study of the as-consolidated samples shows that the quasicrystalline phase remained in the samples if consolidation temperature was lower than 500°C. Consolidation at higher temperatures results in disappearing of the QC and formation of crystalline phases, such as Al₂Cu and Al₇Cu₂Fe by reaction between QC and aluminium matrix. SEM study of microstructure of the composite alloys shows an absence of open porosity in the consolidated bulk samples. Besides rather large particles of reinforcing phase of about 20 μm there are also very small particles of less than 1 μm. The uniformity of particles distribution in the matrix increases with increase in the milling duration. Microhadrness measurements and compression tests were performed, an effect of the treatment parameters on the compressive strength was studied.     

Effect of milling time,MWCNT content,and annealing temperature on microstructure and hardness of Fe/MWCNT nanocomposites synthesized by high-energy ball milling

Nanocrystalline pure Fe and Fe/MWCNT nanocomposites powders with 0.25, 0.5, 1, and 10 wt% MWCNT contents were synthesized by high-energy ball milling (HEBM). The as-milled powders were cold-compacted and annealed at 400 °C and 600 °C for 1 h in Ar atmosphere. The effect of ball milling on pristine MWCNT and Fe/MWCNT composite powders was also investigated as a function of milling time up to 20 h. The physical properties of MWCNT were imaged by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) before and after HEBM. The structural damage of MWCNT as a function of milling time and MWCNT content was studied using Raman spectroscopy. The structural characterization of MWCNT and Fe/MWCNT composites was conducted by X-ray diffraction (XRD) as a function of milling time, MWCNT content, and annealing temperature. The chemical properties of the synthesized composite powders were investigated using X-ray photoelectron spectroscopy (XPS). The microhardness test was performed to assess the effect of milling time, annealing temperature, and MWCNT content on the mechanical properties. The results indicated that after the ball milling process, the structure of MWCNT was destroyed, and the formation of the amorphous carbon phase was observed, which was confirmed by XRD and TEM analyses. In addition, decreased defect and carbon intensity ratios (I_D/I_G) were calculated from the Raman results with longer ball milling processes, which is attributed to the destruction of carbon bonds. The XPS results confirmed the presence of FeC bonds as a result of the formation of carbide phases. A fine dispersion of precipitated carbides determined by TEM is found to promote the grain size stability below 100 nm in the nanocrystalline Fe matrix. The results from the micro-hardness tests showed that Orowan particle strengthening resulting from the carbide formation, as well as grain size hardening, is an important contributor to strengthening in Fe/MWCNT composites.     

Synthesis and thermal stability of ball-milled and melt-quenched amorphous and nanostructured Al-Ni-Nd-Co alloys

In this work the Al₈₅Ni₉Nd₄Co₂ alloy was used as a starting point for examining the possibility of forming bulk glassy Al-based materials by combining rapid quenching and ball milling techniques. Fine glassy powders were obtained by ball milling melt-spun amorphous ribbons using a severe cryogenic processing regime. The thermal stability data of the powders as obtained by constant-rate heating and isothermal DSC experiments together with viscosity measurements are discussed with respect to feasible consolidation conditions. The powder compaction was done by two methods (uni-axial hot pressing and extrusion) at 513 K for up to 15 min. Only the uni-axial hot pressing led to bulk Al₈₅Ni₉Nd₄Co₂ samples with similar glassy structure and Vickers microhardness values comparable to those of the initial melt-spun ribbons.     

Magnetic susceptibility,electrical resistance,and density of Al<Subscript>62</Subscript>Cu<Subscript>25.5</Subscript>Fe<Subscript>12.5</Subscript> alloy at high temperatures

Results are given of an investigation of magnetic susceptibility, electrical resistance, and density of Al₆₂Cu_25.5 5Fe_12.5 alloy in the solid and liquid states. It is found that the behavior of the investigated properties at temperatures above the melting point is abnormal. The results are discussed assuming the existence of long-lived (metastable) microregions in the melts.     

Structural analysis of mechanically alloyed nanocrystalline Fe75Si15Al10 powders

Nanocrystalline Fe₇₅Si₁₅Al₁₀ powders were synthesized by ball milling elemental powders followed by heat treatment at elevated temperatures. The milling process produced a non-equilibrium solid solution of bcc α-Fe(Si,Al). This solid solution transforms into an ordered DO₃ crystal structure after annealing at 700 °C. Growth of the DO₃ structure with annealing time was studied by comparing the corresponding average crystallite size and long-range order parameter. The milling process was studied by analyzing the X-ray diffraction patterns using the Williamson-Hall and Ungar et al. methods. The applicability of the two methods for the present data is discussed.     

Microstructure and martensitic transformation in Si-coated TiNi powders prepared by ball milling

Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO₂ occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powders were recovered and Ti₄Ni₄Si₇ was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.     

Synthesis of an icosahedral quasicrystalline phase in the Al-Cu-Fe system via mechanical activation

A quasicrystalline compound of composition Al₆₄Cu₂₄Fe₁₂ has been prepared through mechanical activation. We have studied the morphology of powder particles after heat treatment under various conditions, identified the sequence of phase transformations in Al-Cu-Fe alloys in the stability region of the ico-phase, and optimized conditions for the preparation of powders containing the maximum possible percentage of the quasicrystalline phase.     

In-situ fabrication of Al3V/Al2O3 nanocomposite through mechanochemical synthesis and evaluation of its mechanism

In this research, in situ fabrication of Al₃V based nanocomposite and its formation mechanism have been investigated. In order to synthesize Al₃V/Al₂O₃ nanocomposite, a mixture of Al and V₂O₅ powders was subjected to high-energy ball milling and the nanocomposite was produced through a mechanochemical reaction. The produced structure was isothermally heat-treated at 500–600 °C for 0.5–2 h under argon atmosphere. In order to evaluate the structural changes during milling and annealing, the synthesized powders were characterized by X-ray diffraction (XRD). Moreover, the powder morphological changes were studied by scanning electron microscopy (SEM). It was observed that the reaction between Al and V₂O₅ occurred after about 30 min and, the Al₃V and Al₂O₃ were formed in nanocrystalline structure with the continuing mechanical milling. Calculation of adiabatic temperature confirmed that reaction took place in combustion mode. In final stage of milling up to 40 h; it was observed that the Al₃V decomposed to Al and V so that the optimum time of milling to achieve fabrication of nanocomposite was determined to be about 20 h. Calculations based on Miedema’s model verified partial disordering of Al₃V during further milling and annealing of as-milled powder at 600 °C led to the ordering of Al₃V. The crystallite size of Al₃V and Al₂O₃ after annealing at 600 °C for 2 h remained in nanometer scale. So the final product appeared to be stable even after annealing.     

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.     

Studies of interfaces in Al65Cu20Fe15

The study of interfaces in quasicrystalline alloys is relatively new. Apart from the change in orientation, symmetry and chemistry which can occur across homophase and heterophase boundaries in crystalline materials, we have the additional, exciting possibility of an interface between quasicrystalline and its rational approximant. High resolution electron microscopy is a powerful technique to study the structural details of such interfaces. We report the results of a HREM study of the interface between the icosahedral phase and the related Al₁₃Fe₄ type monoclinic phase in melt spun and annealed Al₆₅Cu₂₀Fe₁₅ alloy.     

Synthesis of Cu–Zr–Al/Al2O3 amorphous nanocomposite by mechanical alloying

Two routes were used to produce Cu–Zr–Al/Al₂O₃ amorphous nanocomposite. First route included mechanical alloying of elemental powders mixture. In second route Cu₆₀Zr₄₀ alloy was synthesized by melting of Cu and Zr. Cu₆₀Zr₄₀ alloy was then ball milled with Al and CuO powder. It was not possible to obtain a fully amorphous structure via first route. The mechanical alloying of Cu₆₀Zr₄₀, Al and CuO powder mixture for 10 h led to the reaction of CuO with Al, forming Al₂O₃ particulate, and concurrent formation of Cu₆₂Zr₃₂Al₄ amorphous matrix. The thermodynamical investigations on the basis of extended Miedema’s model illustrated that there is a strong thermodynamic driving force for formation of amorphous phase in this system. Lack of amorphization in first route appeared to be related to the oxidation of free Zr during ball milling.     

Synthesis,structure, and mechanical response of Cr0.26Fe0.24Al0.5 and Cr0.15Fe0.14Al0.30Cu0.13Si0.28 nanocrystallite entropy alloys

The present research work has concentrated to synthesize nanocrystalline (NC) Cr_0.26Fe_0.24Al_0.5 (medium entropy alloy, 3E-MEA) and Cr_0.15Fe_0.14Al_0.30Cu_0.13Si_0.28 (high-entropy alloy, 5E-HEA) non-equiatomic (equal weight fraction) alloys through mechanical alloying (MA); which studied the influence of entropy effect on structural properties, microstructural characterization, and mechanical behaviour. Further, the same non-equiatomic ratio of two coarse grain alloys (CGAs) was manufactured by conventional powder metallurgy (PM) route (blending method, 3E-CGA, 5E-CGA) for comparison. All synthesized powders were hot-pressed (HPed) at 723 k for 30 min subsequently mechanical properties in terms of compressive stress-strain and hardness were examined. The samples of as-milled powders, HPed, and fractured were investigated using X-ray diffraction (XRD) and advanced electron microscopes. The HPed sample of 3E-MEA of Cr_0.26Fe_0.24Al_0.5 produced 94% BCC and 6% FCC crystal structures due to more dissolution of Al atoms in the stronger bonding atoms of Cr-Fe lattice. Whereas 5E-HEA of Cr_0.15Fe_0.14Al_0.30Cu_0.13Si_0.28 sample has exhibited 72.1% FCC phase and 27.9% BCC phase due to balance between the dissolution of FCC elements (Al, Cu, Si) and BCC elements (Cr, Fe). Further, 3E-MEA and 5E-HEA have exhibited the ultimate compressive strength (UCS) of 1278 ± 6.75 MPa and 2060 ± 2.8 MPa respectively whereas the corresponding conventionally blended alloys produced 268 ± 5 MPa and 615 ± 3 MPa for 3E-CGA and 6E-CGA respectively. Vicker’s hardness strength (VHS) of 5E-HEA of Cr_0.15Fe_0.14Al_0.30Cu_0.13Si_0.28 has exhibited 68% more when compared to 3E-MEA of Cr_0.26Fe_0.24Al_0.5, 3.26 times higher compared to blended alloys. Further, several strengthening mechanisms on the mechanical behaviour of MEA and HEA were investigated in which dislocation strengthening mechanisms followed by solid solution strengthening mechanisms have influenced more as compared to grain boundary strengthening mechanisms.     

Preparation and study of Al-Cr,Al-Cr-Mn quasicrystalline powders

The production technique of Al-Cr, Al-Cr-Mn alloy quasicrystalline powders and their morphology, composition, diffraction pattern and thermal stability were studied. Computer processing of elevated-temperature X-ray diffraction data, enabled kinetic phase transformation diagrams to be plotted. It was shown that in Al-Cr, Al-Cr-Mn alloys, the composition and cooling rate dramatically affect the formation of the icosahedral phase; at a cooling rate of 10⁵−10⁶ Ks⁻¹, nearly full icosahedral phase Al₈₂Cr₁₈, Al₈₂ (Mn, Cr)₁₈ powders could be produced. For Al-Cr alloy, the thermal stability of quasicrystalline phase is improved with the increasing chromium content. The addition of the third constituent, manganese, can also improve the thermal stability of quasicrystalline phase.     

Role of Fe substitution and quenching rate on the formation of various quasicrystalline and related phases

We have investigated Fe substituted versions of the quasicrystalline (qc) alloy corresponding to Al₆₅Cu₂₀(Cr, Fe)₁₅ with special reference to the possible occurrence of various quasicrystalline and related phases. Based on the explorations of various compositions it has been found that alloy compositions Al₆₅Cu₂₀Cr₁₂Fe₃ and Al₆₅Cu₂₀Cr₉Fe₆ exhibit interesting structural phases and features at different quenching rates. At higher quenching rates (wheel speed ～ 25 m/sec) all the alloys exhibit icosahedral phase. For Al₆₅Cu₂₀Cr₁₂Fe₃ alloy, however, both the icosahedral and even the decagonal phases get formed at higher quenching rates. At higher quenching rate, alloy having Fe 3 at % exhibits twobcc phases,bccI (a = 8.9 å) andbccIIa = 15.45 å). The orientation relationships between icosahedral and crystalline phases are: Mirror plane ∥ [001] _bcc I and [351] _bcc II, 5-fold ∥ [113] _bcc II and 3-fold ∥ [110]inbcc II. At lower quenching rate, the alloy having Fe 6 at % exhibits orthorhombic phase (a = 23.6 å,b = 12.4 å,c = 20.1 å). Some prominent orientation relationships of the orthorhombic phase with decagonal phase have also been reported. At lower quenching rate (～ 10 m/sec), the alloy (Al₆₅Cu₂₂Cr₉Fe₆) shows the presence of diffuse scattering of intensities along quasi-periodic direction of the decagonal phase. For making the occurrence of the sheets of intensities intelligible, a model based on the rotation and shift of icosahedra has been put forward.     

Influence of milling conditions on the segregation-induced instability of Pd3Zr

Structural transformations in Pd₃Zr intermetallid upon ball-milling and subsequent annealing was studied under different milling conditions. The compound was milled in a medium energy vibrating mill with tungsten-carbide vial and ball as well as in a high energy planetary mill with stainless steel components. The milling processes were performed in highly purified Ar gas and in a mixture of Ar+10%H gases, respectively. The as-milled powders were annealed in the temperature range of 500-1300°C, and the structural transformations were studied by X-ray diffraction with monochromatic Cu K_α1 radiation. It is shown that the impurities introduced from milling components and the oxygen contamination from milling atmosphere strongly influence the stability of the nanocrystalline Pd₃Zr during the mechanical- and subsequent heat treatments. The evolution and coexistence of Pd(Zr) with Pd₃Zr, induced by the preparation and annealing processes, are discussed.     

Elaboration of the Cu3Si compound using a mechanically activated annealing process

The mechanically activated annealing process were used to produce Cu₃Si compound. This process results from the combinaison of two steps, the first is a mechanical activation of the 3Cu + Si powders mixture, the second consists of the annealing of as-milled powders. Based on X-ray diffraction experiment, scanning electron microscopy, the as-milled powders and M2AP end-products were characterized. Various process controlling parameters such as mechanical activation conditions were studied. In the same time, a sutdy of the reactivity ofCu₃Si towards CuCl were performed to compare the M2AP end-products behavior with that of the Cu₃Si reference powder.     

Al–Cu–Fe coatings manufactured by the flame spraying process

Two-hour milled (activated) Al–20Cu–15Fe (at%) powders were subjected to annealing at 600°C for 1?h. The phase and microstructural evolutions were characterized by X-ray diffractometry and scanning electron microscopy. Al₇Cu₂Fe and Al₆₀Cu₃₀Fe₁₀ phases were formed after annealing. Both annealed and milled powders were consolidated using the flame spraying process. In both cases, FeAl(Cu) was the major phase while some oxides and α-Fe(Al,Cu) were also found. The coating produced from the milled powder was severely cracked and showed higher oxide content. The coating prepared from the annealed powder showed better quality. It was annealed at 600°C for 1?h to investigate the thermal stability of the various phases. All phases persevered after annealing while the Fe₂Al₅ phase was formed as a new phase.