Glass formability and structural stability of Al-based alloy systems (original) (raw)
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Effect of Ni–Al atomic ratio on glass formation in La–Al–Cu–Ni bulk metallic glasses
Journal of Alloys and Compounds, 2009
Glass forming ability (GFA) and thermal properties were investigated for La 62 Al 14 (Cu 1−x Ni x) 24 (x = 0.2, 0.4, 0.6 and 0.8) bulk metallic glasses (BMGs). The experimental results show that in the La-based La-Al-(Cu-Ni) pseudo-ternary system, optimum glass formation actually occurs at the Ni:Al ratio of 1:1. It has been found that the GFA is much better in the range of unstable intermetallic compound (AlNi) than that of adjacent stable intermetallic compound (AlNi 3). The asymmetry of negative heat of mixing between the atomic pairs of La-Cu and La-Ni, Al-Cu and Al-Ni is also considered as another influencing factor of GFA. It might be an effective way to develop and design BMGs by adjusting the Ni-Al atomic ratio in Al-Ni-contained alloy systems.
Crystallisation behaviours of Al-based metallic glasses: Compositional and topological aspects
Journal of Alloys and Compounds, 2009
The different types of thermal crystallisation behaviours observed during continuous heating of Al-based metallic glasses have been successfully associated with the topological instability criterion, which is simply calculated from the alloy composition and metallic radii of the alloying elements and aluminium. In the present work, we report on new results evidencing the correlation between the values of and the crystallisation behaviours in Al-based alloys of the Al-Ni-Ce system and we compare the glass-forming abilities of alloys designed with compositions corresponding to the same topological instability condition. The results are discussed in terms of compositional and topological aspects emphasizing the relevance of the different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallisation.
Journal of Applied Physics, 2014
To clarify the correlation of medium-range order (MRO) structure with glass forming ability (GFA) of Al-based metallic glasses, Al 86 Ni 14-a Y a (a ¼ 2$9 at. %) metallic glasses were analyzed by x-ray diffraction in detail and further verified by synchrotron high-energy x-ray diffraction. The prepeak that reflects the MRO structural evolution was found to be much sensitive to alloy composition. We have proposed an icosahedral supercluster MRO structure model in Al-TM (transition metal)-RE (rare earth metal) system, which consists of 12 RE(TM)-centered clusters on the vertex of icosahedral supercluster, one RE(TM)-centered clusters in the center, and TM(RE) atoms located at RE(TM)-centered cluster tetrahedral interstices in the icosahedral supercluster. It was indicated that the MRO structural stability mainly depends on the interaction of efficient dense packing and electrochemical potential equalization principle. The Al 86 Ni 9 Y(La) 5 alloys present good GFA due to the combination of the two structural factors. V
Glass-Forming Ability and Ductility of Zr-Based and Al-Rich Bulk Metallic Glasses
Advanced Engineering Materials, 2008
The glass-forming ability and mechanical properties in the equivalent Zr-Al-CuNiCo three-component phase diagram was investigated as a function of Al content along the Zr 63-x Al x Cu 24 Ni 10 Co 3 (at.%) with 7 ≤ × ≤ 20 isoconcentration line. With a critical cooling rate of about 250 Ks-1 , the limit of bulk metallic glass formation was obtained at 16 at.% Al. Higher Al concentrations resulted in a composite amorphous/crystalline microstructure with varying crystalline volume fractions until at 21 at.% Al a fully crystalline alloy was obtained. Mechanical properties were investigated by nanoindentation and ultrasonic sound velocity measurements showing an increase in hardness and bulk modulus of the fully amorphous alloys as a function of the Al concentration. The ratio of the shear to the bulk modulus exhibited a pronounced minimum for 13 at.% Al. The mechanical and calorimetric data showed a unique correlation between the elatsic moduli, hardness, and the concentration dependence of the glass-transition temperature. The crystalline phase in the composite microstructure turned out to be brittle and, thus, no improvement in ductility was obtained. The early stages of solid-state amorphization by mechanical alloying of elemental powders of composition Zr 60 Al 10-Cu 18 Ni 9 Co 3 [1] were characterized by the formation of a variety of amorphous phases including some Al-rich compositions. [2] As such, it appeared interesting to find out if these
Glass forming ability of the Al–Ce–Ni system
Journal of Non-Crystalline Solids, 2008
In the present work, the glass forming ability (GFA) and its compositional dependence on Al-Ni-Ce system alloys were investigated as a function of several thermal parameters. Rapidly quenched Al 85 Ni 15ÀX Ce X (X = 4,5,6,7,10), Al 90 Ni 5 Ce 5 , Al 89 Ni 2.4 Ce 8.6 , Al 80 Ni 15.6 Ce 4.4 and Al 78 Ni 18.5 Ce 3.5 amorphous ribbons were produced by melt-spinning and the structural transformation during heating was studied using a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results showed that the GFA and the thermal stability in the Al-rich corner of Al-Ni-Ce system alloys were enhanced by increasing the solute content and specifically the Ce content.
The atomic structure of aluminum based metallic glasses and universal criterion for glass formation
Journal of Non-Crystalline Solids, 1996
It recently became recognized that several phenomena related to the formation of glass or liquid for metallic alloy systems can be explained in terms of a universal criterion for glass formation. These include the composition limit for glass formation by rapid cooling of a liquid alloy, that for solid state amorphization by radiation, thermal or mechanical alloying, and the conditions for glass transition and melting of a crystalline alloy. The aluminum-based metallic glasses, however, appear to be an exception for this rule. It is shown that, by modifying the rule to allow for the interstitial site occupation, the composition range of glass formation for aluminum-based glasses can also be explained by the same principle of local topological instability.
Studies on crystallization behaviour and mechanical properties of Al-Ni-La metallic glasses
Bulletin of Materials Science, 2008
Alloy ingots with nominal composition, Al 92-x Ni 8 La x (x = 4 to 6) and Al 94-x Ni 6 La x (x = 6, 7), were prepared by induction melting in a purified Ar atmosphere. Each ingot was inductively re-melted and rapidly solidified ribbons were obtained by ejecting the melt onto a rotating copper wheel in an argon atmosphere. The crystallization behaviour of melt-spun amorphous ribbon was investigated by means of differential scanning calorimetry (DSC), X-ray diffractometry and transmission electron microscopy. DSC showed that Al 86 Ni 8 La 6 alloy undergoes a three-stage and rest of the alloys undergo a two-stage crystallization process upon heating. The phases responsible for each stage of crystallization were identified. During the first crystallization stage fcc-Al precipitates for low La-containing alloys and for higher La-containing alloys a bcc metastable phase precipitates. The second crystallization stage is due to formation of intermetallic compounds along with fcc-Al. Microhardness of all the ribbons was examined at different temperatures and correlated with structural evolutions. Precipitation strengthening of nano-size fcc-Al is responsible for maximum hardness in these annealed alloys.
9- Wang JQ Intermetallics 2012 Al-based metallic glass
In order to stabilize the supercooled liquid and enhance the glass forming ability of Al-based glass forming alloy, the alloying design based on minor Ca substitution for Al was examined to retard the precipitation of face-centered-cubic (FCC) Al. Calcium was selected as the alloying element, because it has a large negative mixing heating with Al but a positive value with the other components. This is anticipated to facilitate formation of AleCa clusters and then inhibit the diffusion of Al atoms which is thought to be the dominant reason that limits the glass forming ability (GFA) of Al-based alloys. The proposed strategy was confirmed in experiments by the observation of a greatly increased reduced glass transition temperature, T rg ¼ T g /T l (T g the glass transition temperature and T l the liquidus temperature), the increased the activation energy for crystallization, and the increased activation energy for diffusion. The Al 85Àx Y 8 Ni 5 Co 2 Ca x (x ¼ 0.5e5) system is found to possess extraordinarily high T rg ¼ 0.613 far exceeding that for any known Al-based glass forming alloys.
Topological instability and glass forming ability of Al–Ni–Sm alloys
Journal of Alloys and Compounds, 2011
The thermal crystallization of Al-based metallic glasses can be described in association with the topological instability criterion. In the present work, we report on the crystallization behavior and glass forming ability of Al-rich, Al-Ni-Sm alloys, designed with compositions corresponding to the same topological instability condition of ≈ 0.1. Amorphous melt-spun alloys were prepared with the following compositions, varying the ratio of Ni and Sm elements: Al 87.5 Ni 4 Sm 8.5 , Al 83.5 Ni 10 Sm 6.5 , Al 80.5 Ni 14.5 Sm 5 and Al 76.5 Ni 20.5 Sm 3. The glass forming ability of each alloy composition was evaluated based on the thermal parameters obtained from DSC runs and on X-ray diffraction patterns. Better glass forming ability was observed in compositions whose Sm content was increased and Ni content reduced. Thermal crystallization of the alloys with low Sm content showed only one crystallization peak and no glass transition event. In alloys with higher rare-earth content, a glass transition event was clearly detected before the crystallization event. The results are interpreted considering the different types and proportions of Sm-Al and Ni-Al clusters that can be formed in the alloys along the ≈ 0.1 line. They also emphasize the relevance of these different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallization.
Glass forming ability and crystallisation processes within the Al–Ni–Sm system
Journal of Non-Crystalline Solids, 2001
Several melt-spun ribbons of dierent compositions in the Al-rich corner of the Al±Ni±Sm ternary system were analysed by means of X-ray diraction (XRD) and dierential scanning calorimetry (DSC) in order to determine their thermal stability and to understand the nanocrystallisation process. Out of all the compositions analysed, only three were found to be completely amorphous, whereas the others were partially crystallised. The activation energies of the a-Al nanocrystallisation were evaluated using the Kissinger method. Isothermal DSC scans revealed the existence of quenched-in nuclei in the more unstable amorphous alloys. These quenched-in nuclei are probably due to the meltspinning process and the crystalline structure after devitri®cation is strongly dependent on them.