The Solidification Path of the Complex Metallic Al-Mn-Be Alloy

The solidification paths of the Al86.1Mn2.5Be11.4 and Al84Mn5.1Be10.9 alloys, melt spun, cast into a copper mould and controlled cooled (during DSC) were investigated by means of light-optical microscopy (LOM), differential scanning calorimetry (DSC) combined with thermogravimetry (TG) or simultaneous thermal analysis (STA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and the X-ray diffraction (XRD) line in Elletra Trieste, Italy. The constitutions of samples from both alloys were examined in all three states, i.e., after melt spinning, after casting into a copper mould and after differential scanning calorimetry. It was established that in the cast and controlled-cooled specimens the alloys consisted of an aluminium-rich αAl-matrix, and the Al4Mn and Be4AlMn phases. In the case of casting and DSC the primary crystallization began with the precipitation of the Be4AlMn phase, followed by what can most likely be characterized as a uni-variant binary eutectic reaction L → (Be4AlMn + Al4Mn). The solidification process continued with an invariant ternary eutectic reaction, where the remaining melt (L) formed the heterogeneous structure (αAl + Al4Mn + Be4AlMn) or a ternary eutectic. When extremely high cooling rates were employed, as is the case with melt-spinning, the constituting phases of both alloys were precipitated in a very small form and the Be4AlMn phase was completely absent in the form of primary polygonal particles and replaced by the icosahedral quasicrystalline phase or the i-phase. There was also no evidence of the Al4Mn phase. The distribution, size and shape of all the constituents in the melt-spun alloys also varied from the contact surface towards the free surface of the ribbons. The smallest constituents were established at the contact surface, measuring less than 0.1 μm, to 0.5 μm at the free surface. The grains of the aluminium-rich matrix had mean diameters of less than 20 μm, close to the free surface, down to 1 μm at the contact surface.</p

Plasmonic Refractive Index Sensing Based on Interference in Disordered Composite Films

The strong dispersion in the effective optical constants of plasmonic nanocomposite films is used to generate interference effects that are highly sensitive to changes in the dielectric environment of particles. Numerical simulations show that reflectance measurements on metal nanoparticle systems close to a metallic substrate have larger sensitivities to changes in the surrounding refractive index than the standard transmittance measurements of the same system when placed on a transparent substrate. The scheme is particularly advantageous in case of disordered nanoparticle systems, where the difference between reflectance and transmittance‐based sensing approaches is enhanced due to local‐field fluctuations that modify the effective optical constants dispersion. Exceptional to most plasmonic applications, in the present case, a disordered system provides larger sensitivity and figure of merit than its ordered counterpart. The key concepts suggested from numerical calculations are verified by the fabrication of metal island films coated with different dielectric layers, that confirm the superiority of the reflectance‐based sensing scheme. Overall, the present approach profits from the disorder to improve refractive index sensitivity in metal nanoparticle systems that are produced with industrially appealing techniques. Thus, the proposed scheme may be valuable for the broad implementation of low‐cost and highly efficient plasmonic sensors

Shapes of the icosahedral quasicrystalline phase in melt-spun ribbons

The shapes of icosahedral quasicrystalline (IQC) particles were determined in melt-spun ribbons of alloys based on the Al-Mn-Be alloy system. The sizes of the quasicrystalline particles ranged from a few tenths of nanometres up to 1m. Therefore, different methods were employed for characterizing their shapes: projection of quasicrystalline particles using transmission electron microscopy (TEM), cross-sections of IQCs on metallographically polished surfaces, and observation of deep-etched samples and extracted particles using a scanning electron microscope (SEM). It was discovered that icosahedral quasicrystalline particles preferentially grow in three-fold directions and have a tendency for faceting and adopting the shape of a pentagonal dodecahedron. The evolution of quasicrystalline shapes is systematically presented

In situ TEM study of precipitation in a quasicrystal-strengthened Al-alloy

Precipitation kinetics and mechanisms within an Al-Mn-Be-Cu quasicrystal strengthened alloy at 300°C were studied using in-situ transmission electron microscopy. The alloy was cast into a copper mould. Quasicrystalline precipitates formed throughout the Al-rich solid solution, whilst heterogeneous formations of Al2Cu and T-phase occurred on icosahedral quasicrystalline particles formed during solidification. The formation of quasicrystalline particles and T-phase was limited by manganese diffusivity, whilst that of Al2Cu by copper diffusivity. The precipitation produced only a small hardening effect

Način skrućivanja kompleksne metalne Al-Mn-Be legure

The solidification paths of the Al86.1Mn2.5Be11.4 and Al84Mn5.1Be10.9 alloys, melt spun, cast into a copper mould and controlled cooled (during DSC) were investigated by means of light-optical microscopy (LOM), differential scanning calorimetry (DSC) combined with thermogravimetry (TG) or simultaneous thermal analysis (STA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and the X-ray diffraction (XRD) line in Elletra Trieste, Italy. The constitutions of samplesfrom both alloys were examined in all three states, i.e., after melt spinning, after casting into a copper mould and after differential scanning calorimetry. It was established that in the cast and controlled-cooled specimens the alloys consisted of an aluminium-rich ▫$alpha$▫Al-matrix, and the Al4Mn and Be4AlMn phases. In the case of casting and DSC the primary crystallization began with the precipitation of the Be4AlMn phase, followed by what can most likely be characterized as a uni-variant binary eutectic reaction L > (Be4AlMn + Al4Mn). The solidification process continued with an invariant ternary eutectic reaction, where the remaining melt (L) formed the heterogeneous structure (▫$alpha$▫Al + Al4Mn + Be4AlMn) or a ternary eutectic. When extremely high cooling rates were employed, as is the case with melt-spinning,the constituting phases of both alloys were precipitated in a very small form and the Be4AlMn phase was completely absent in the form of primary polygonal particles and replaced by the icosahedral quasicrystalline phase or the i-phase. There was also no evidence of the Al4Mn phase. The distribution, size and shape of all the constituents in the melt-spun alloys also varied from the contact surface towards the free surface of the ribbons. The smallest constituents were established at the contact surface, measuring less than 0.1 ▫$mu$▫m, to 0.5 ▫$mu$▫m at the free surface. The grains of the aluminium-rich matrix had mean diameters of less than 20 ▫$mu$▫m, close to the freesurface, down to 1 m at the contact surface.Načini skrućivanja Al86.1B2.5 Be11.4 i Al84Mn5.1Be10.9 legura dobivenih lijevanjem pri velikim brzinama hlađenja ("melt-spinning" metoda), u bakrenu kokilu i uz kontrolirano hlađenje (za vrijeme DSC) istraživani su metodama optičke mikroskopije (LOM), diferencijalno pretražne kalorimetrije (DSC) u kombinaciji s termogravimetrijom (TG) ili simultanom toplinskom analizom (STA), pretražne elektronske mikroskopije (SEM), transmisijske elektronske mikroskopije (TEM), spektroskopije Augerovih elektrona (AES) i rendgenske difrakcije (XRD). Konstituenti uzoraka iz obje legure su ispitivani za tri različita stanja, tj. nakon izrazito brzog hlađenja, lijevanja u bakrenu kokilu i nakon diferencijalno pretražne kalorimetrije. Utvrđeno je da su se uzorci legura u lijevanom i kontrolirano hlađenom stanju sastojali od aluminijem bogate αAl-osnove, te Al10Mn3 i Be4AlMn faza. U slučaju lijevanja i diferencijalno pretražne kalorimetrije primarna je kristalizacija započela precipitacijom B4AlMn faze što se može najvjerojatnije okarakterizirati kao univarijantna binarna eutektička reakcija L > (Be4AlMn + Al10Mn3). Proces skrućivanja je nastavljen s invarijantnom ternarnom eutektičkom reakcijom, gdje preostala talina (L) stvara heterogenu strukturu (αAl + Al10Mn3 + Be4AlMn) ili ternarni eutektik. Kada su korištene izrazito velike brzine hlađenja, kao u slučaju "melt-spinning" metode, konstitutivne faze obiju legura su precipitirale u veoma malom obliku, a Be4AlMn faza bila je potpuno odsutna u obliku primarnih poligonalnih čestica i zamijenjena je "icosahedral" kristaliničnom fazom ili i-fazom. Također nema dokaza o prisutnosti Al10Mn3 faze. Raspodjela, veličina i oblik svih konstituenata u brzo-hladećim legurama su se promijenili od kontakne površine prema slobodnoj površini trakica, s manje od 0.1 µm pa do 0.5 µm kod slobodne površine. Zrna aluminijem bogate osnove imala su, blizu slobodne površine, srednji promjer manji od 20 µm, a kod kontakne površine srednji promjer zrna se smanjio na 1 µm

Utjecaj brizne hlađenja na mikrostrukturu legure Al94Mn2Be2Cu2

In this study the effect of the cooling rate on the microstructure of Al94 Mn2 Be2 Cu2 alloy was investigated. The vacuum induction melted and cast alloy was exposed to different cooling rates. The slowest cooling rate was achieved by the DSC (10 K·min^−1), the moderate cooling rate succeeded by casting in the copper mould (≈1 000 K·s−1) and the rapid solidification was performed by melt spinning (up to 10^6 K·s^−1). The microstructure of the DSC-sample consisted of α-Al matrix, and several intermetallics: τ1-Al29 Mn6 Cu4 , Al4 Mn, θ-Al2 Cu and Be4 Al(Mn,Cu). The microstructures of the alloy at moderate and rapid cooling consisted of the α-Al matrix, i-phase and θ-Al2 Cu. Particles of i-phase and θ-Al2 Cu were much smaller and more uniformly distributed in melt-spun ribbons.U ovoj je studiji istraživan utjecaj brzine hlađenja na mikrostrukturu legure Al94Mn2Be2Cu2. Legura sintetizirana vakuumskim indukcionim taljenjem i postupkom lijevanja bila je izložena različitim brzinama hlađenja. Najsporije je bilo hlađenje kod DSC (10 K•min-1), umjerene brzine hlađenja prilikom lijevanja u bakreni kalup (≈1 000 K•s-1) a najviše brzine skrućivanja postignute su pomoću metode melt spinning (do 106 K•s-1). Mikrostruktura DSC uzoraka sastoji se od matrice α-Al i nekoliko intermetalnih faza: τ1-Al29Mn6Cu4, Al4Mn, θ-Al2Cu i Be4Al(Mn,Cu). Mikrostruktura legura umjereno i brzo hlađenih sastoji se od matrice α-Al, i-faze i θ-Al2Cu. Čestice i-faze i θ-Al2Cu mnogo su manje i ravnomjerno raspoređene u trakama izrađenima metodom melt spinning