The ageing behavior of Al
90−
x
Ni
6La
4+
x
(
x
=
0–3) amorphous alloys under ambient temperature (20–50
°C) has been studied. Partial crystallization has been observed in all alloys after several ...years of ageing under ambient conditions especially in Al
90Ni
6La
4 and Al
89Ni
6La
5 alloys, where the onset of crystallization temperatures are comparatively lower. The transformations have been studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. These alloys showed two stages of crystallization upon heating. A significant decrease of first stage of crystallization enthalpy was observed after 5.5 years of room temperature ageing and showed a mixed structure containing fcc-Al nanocrystals (20–40
nm) in an amorphous matrix. The results are explained in terms of transformation kinetics at the ageing temperatures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Crystallization behavior and glass transition phenomenon of Al89Ni6La5, Al87Ni6La7 and Al87Ni5La7M1 (M=Ag, Cu) metallic glasses have been studied by temperature modulated differential scanning ...calorimetry (TMDSC). A clear glass transition of these glasses, which could not be detected in conventional differential scanning calorimetry (DSC), even at higher heating rates, was observed through TMDSC measurements. All these glasses undergo two-stages of crystallization on heating. The precipitation and growth of fcc-Al in Al89Ni6La5 and bcc-metastable phase in other alloys are responsible for the first stage of crystallization. The glass transition phenomenon in these alloys except Al87Ni6La7, could not be detected in DSC because the signals are overlapped with the relatively large heat release from the primary crystallization. This was confirmed from the TMDSC measurements. These measurements were necessary for the development of new nanocrystalline/amorphous composite materials.
► Glass formability in Al-based alloys decreases with Ag or Cu addition. ► In TMDSC measurement Tg is clearly observed. ► TMDSC can separate reversible and non-reversible heat flow from total heat flow.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The phase transformation reactions that occur in Al
85Ni
10La
5 alloy during mechanical milling were studied by using fully and partially amorphous ribbons (comprised of fcc-Al, Al
3Ni, Al
11La
3 and ...amorphous phases) as starting materials. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) study showed that the Al
3Ni phase crystallized, whereas the Al
11La
3 phase amorphized during mechanical milling. The results reported herein indicated that, irrespective of the phase constitution of the starting materials, the microstructure that evolved following mechanical milling was comprised of the same phases; namely: fcc-Al, Al
3Ni and amorphous phases. Differential scanning calorimetry (DSC) analysis revealed that the difference in the structural stability of the Al
3Ni and Al
11La
3 phases are related to the chemical short-range order of the solute atoms in the amorphous phase. The results described in this paper provide an alternative approach to study glass forming ability during mechanical milling.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Amorphous Al85Ni10La5 powders were consolidated to cylindrical samples by spark plasma sintering (SPS), and their microstructures and mechanical properties were investigated. When the powders were ...consolidated below the crystallization temperature, an amorphous phase was retained in the consolidated sample. Sintering above the crystallization temperature caused full crystallization. The Vickers hardness of the amorphous-containing sample was about 350 HV in the as-sintered state and increased up to 450 HV by a subsequent heat treatment just below the crystallization temperature. The highest hardness was achieved in a nanocrystalline microstructure. Compression tests revealed the brittle nature of the consolidated samples although the fracture and yield strength was higher than 1 GPa. The brittleness is due to the low relative density of the amorphous-containing samples and the presence of a large amount of intermetallic compounds in the fully crystallized sample.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The mechanical behavior of a nanostructured 5083 Al–Al
85Ni
10La
5 composite that was processed via consolidation of cryomilled 5083 Al and amorphous Al
85Ni
10La
5 powder was investigated in the ...temperature range of 25–400
°C. The devitrified Al
85Ni
10La
5 phase revealed high thermal stability against growth during the consolidation process and resulted in a grain size of approximately 200
nm. The 5083 Al–Al
85Ni
10La
5 composite exhibited superior elevated temperature properties when compared to that of nanostructured or coarse-grained 5083 Al alloy. The mechanical behavior of the 5083 Al–Al
85Ni
10La
5 composite was analyzed in the context of the deformation mechanisms that are active in the 5083 nanostructured matrix.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Amorphous Al
85Ni
10La
5 powders were consolidated to cylindrical samples by spark plasma sintering (SPS), and their microstructures and mechanical properties were investigated. When the powders were ...consolidated below the crystallization temperature, an amorphous phase was retained in the consolidated sample. Sintering above the crystallization temperature caused full crystallization. The Vickers hardness of the amorphous-containing sample was about 350
HV in the as-sintered state and increased up to 450
HV by a subsequent heat treatment just below the crystallization temperature. The highest hardness was achieved in a nanocrystalline microstructure. Compression tests revealed the brittle nature of the consolidated samples although the fracture and yield strength was higher than 1
GPa. The brittleness is due to the low relative density of the amorphous-containing samples and the presence of a large amount of intermetallic compounds in the fully crystallized sample.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The mechanical behavior of a nanostructured 5083 Al-Al85Ni10La5 composite that was processed via consolidation of cryomilled 5083 Al and amorphous Al85Ni10La5 powder was investigated in the ...temperature range of 25-400 deg C. The devitrified Al85Ni10La5 phase revealed high thermal stability against growth during the consolidation process and resulted in a grain size of approximately 200 nm. The 5083 Al-Al85Ni10La5 composite exhibited superior elevated temperature properties when compared to that of nanostructured or coarse-grained 5083 Al alloy. The mechanical behavior of the 5083 Al-Al85Ni10La5 composite was analyzed in the context of the deformation mechanisms that are active in the 5083 nanostructured matrix.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
An Al
85
Ni
10
La
5
amorphous alloy, produced via gas atomization, was selected to study the mechanisms of nanocrystallization induced by thermal exposure. High resolution transmission electron ...microscopy results indicated the presence of quenched-in Al nuclei in the amorphous matrix of the atomized powder. However, a eutectic-like reaction, which involved the formation of the Al, Al
11
La
3
, and Al
3
Ni phases, was recorded in the first crystallization event (263°C) during differential scanning calorimetry continuous heating. Isothermal annealing experiments conducted below 263°C revealed that the formation of single fcc-Al phase occurred at 235°C. At higher temperatures, growth of the Al crystals occurred with formation of intermetallic phases, leading to a eutectic-like transformation behaviour at 263°C. During the first crystallization stage, nanocrystals were developed in the size range of 5 ∼ 30 nm. During the second crystallization event (283°C), a bimodal size distribution of nanocrystals was formed with the smaller size in the range of around 10 ∼ 30 nm and the larger size around 100 nm. The influence of pre-existing quenched-in Al nuclei on the microstructural evolution in the amorphous Al
85
Ni
10
La
5
alloy is discussed and the effect of the microstructural evolution on the hardening behaviour is described in detail.
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