This study presents a unique Mg-based alloy composition in the Mg–Zn–Yb system which exhibits bulk metallic glass, metastable icosahedral quasicrystals (iQCs), and crystalline approximant phases in ...the as-cast condition. Microscopy revealed a smooth gradual transition from glass to QC. We also report the complete melting of a metastable eutectic phase mixture (including a QC phase), generated via suppression of the metastable-to-stable phase transition at high heating rates using fast differential scanning calorimetry (FDSC). The melting temperature and enthalpy of fusion of this phase mixture could be measured directly, which unambiguously proves its metastability in any temperature range. The kinetic pathway from liquid state to stable solid state (an approximant phase) minimizes the free-energy barrier for nucleation through an intermediate state (metastable QC phase) because of its low solid–liquid interfacial energy. At high undercooling of the liquid, where diffusion is limited, another approximant phase with near-liquid composition forms just above the glass-transition temperature. These experimental results shed light on the competition between metastable and stable crystals, and on glass formation via system frustration associated with the presence of several free-energy minima.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
This study presents a series of new Mg–Ag–Y and Mg–Ag–Y–Cu bulk metallic glasses (BMGs) designed to obtain Mg-rich ductile glasses. Compressive ductility is observed in the selected alloys tested, ...involving compressive plastic strains of about 0.6% for the ternary BMGs obtained. Minor amounts of Cu generate a general increase in plastic strain up to about 0.8%. We report on the alloy design methodology, critical casting size, thermophysical properties and compression test data of these new alloys.
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•New Mg–Ag–Y and Mg–Ag–Y–Cu bulk metallic glasses are presented.•Liquid stability region for bulk glass formation is identified in the Mg–Ag–Y system.•Glass formation is predicted by a topological model.•The ternary bulk glasses exhibit plasticity, which is enhanced via Cu addition.•Plasticity is explained via electronic effects in bonding and by mixing enthalpy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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Bulk metallic glasses (BMGs) are multicomponent metal alloys that form a glassy structure with relative ease upon cooling from the melt. Unique to glassy materials is a ...glass-transition (temperature), whereby the vitreous solid relaxes into a supercooled liquid state, leading to a dramatic decrease in viscosity. This softening behaviour allows novel thermoplastic forming and bonding processes to be carried out that are simply unachievable among conventional metal processing methods. The work presented herein utilises this supercooled liquid state by infiltrating carbon fibres within a Mg-based BMG to manufacture fully-dense carbon fibre reinforced BMGs which also exhibit unique secondary forming capabilities.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Magnesium-based bulk metallic glasses (BMGs) exhibit high specific strengths and excellent glass-forming ability compared to other metallic systems, making them suitable candidates for ...next-generation materials. However, current Mg-based BMGs tend to exhibit low thermal stability and are prone to structural relaxation and brittle failure. This study presents a range of new magnesium-precious metal-based BMGs from the ternary Mg-Ag-Ca, Mg-Ag-Yb, Mg-Pd-Ca and Mg-Pd-Yb alloy systems with Mg content greater than 67 at.%. These alloys were designed for high ductility by utilising atomic bond-band theory and a topological efficient atomic packing model. BMGs from the Mg-Pd-Ca alloy system exhibit high glass-forming ability with critical casting sizes of up to 3 mm in diameter, the highest glass transition temperatures (>200 °C) of any reported Mg-based BMG to date, and sustained compressive ductility. Alloys from the Mg-Pd-Yb family exhibit critical casting sizes of up to 4 mm in diameter, and the highest compressive plastic (1.59%) and total (3.78%) strain to failure of any so far reported Mg-based glass. The methods and theoretical approaches presented here demonstrate a significant step forward in the ongoing development of this extraordinary class of materials.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A range of low-density Mg-rich glass-forming compositions from the Mg–Ni–Ca alloy system have been discovered. Distinct maxima in the glass-forming ability were located and shown to produce samples ...of bulk metallic glass dimensions. These bulk glass-forming alloys exhibit the lowest density (<2gcm−3) and highest Mg content (86at.%) of all Mg-based bulk metallic glasses reported to date. Here, the specific alloy design method and a range properties of these amorphous alloys are revealed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► In this work, we report the discovery of the first Ag-based bulk metallic glasses. ► These were found over a broad composition range in the Ag–Mg–Ca–Cu system. ► These alloys were found far from ...ternary eutectic reactions. ► These alloys display critical amorphous casting sizes up to 4
mm in diameter. ► We report their critical casting size and full range of thermophysical properties.
A number of novel silver-based bulk metallic glasses from the Ag–Mg–Ca ternary and Ag–Mg–Ca–Cu quaternary alloy systems have been discovered. These amorphous alloys are located over a broad composition range from (at.%): 30 to 61% Ag, 7 to 38% Mg, 7 to 30% Ca and 0 to 15% Cu often far from ternary eutectic reactions. These new amorphous alloys have been developed in light of their potential applications as functional materials with high electrical and thermal conductivity combined with the superplastic formability of a metallic glass. Reported are the critical casting size and thermophysical properties of these bulk glassy alloys.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This study presents an extensive series of novel bulk metallic glasses (BMGs) which broadly span all three corners of the Mg–Cu–Yb ternary system. Over 30 alloys were synthesised within a wide ...composition range from (at.%): Mg: 13–55, Cu: 17.5–45.5, and Yb: 9–70. In terms of composition, this ternary system is considered to be one of the broadest for bulk glass formation known - this probably due to the three elements' thermodynamic compatibility and unique combinations of atomic radii, which generate specific, favoured structural topologies. The investigation reports the design method, critical casting size, thermophysical characteristics and mechanical properties of these new BMGs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
► New Mg-based alloys in the Mg–Ag–Ca–Cu system with high glass forming ability. ► Critical amorphous castings sizes of up to 5mm using copper mould casting. ► Glassy alloys were discovered/predicted ...using a new topological approach. ► Predicted composition range corresponds with regions of high glass forming ability.
A range of new magnesium-based bulk metallic glasses (BMGs) from the Mg–Ag–Ca, Mg-Cu-Ca ternary and Mg–Ag–Cu–Ca quaternary alloy systems have been discovered using the effective radius ratio method. These alloys are located over a broad composition range from (at.%): Mg – 38–76, Ag – 0–38, Cu – 0–36 and Ca – 7–27, some of which are located far from ternary eutectic reactions. Here, we report the alloy design method, critical casting size and thermophysical properties of these new BMGs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
High entropy alloys (HEAs) show promise as materials for structural applications, even at elevated temperatures. However, their wear behaviour over a wide range of temperatures has not been ...extensively studied. CoCrFeMnNi and AlxCoCrFeNi HEAs were subjected to pin-on-disc dry sliding wear at temperatures between 25 °C and 900 °C against an alumina ball, and the tribological performance benchmarked against AISI 304 and Inconel 718. A detailed characterisation of the wear tracks using electron microscopy and surface profilometry revealed a transition in wear mechanism from abrasive wear at room-temperature to oxidative and delamination wear above 600 °C. The wear performance of the HEAs, AlCoCrFeNi in particular, is substantially enhanced with increasing temperature, surpassing that of Inconel 718 at 900 °C. The enhanced wear performance of the HEAs above 600 °C is attributed to the formation of a compact oxide scale in the contact region, and relative subsurface strengthening in the form of a fine-grained recrystallised structure containing precipitation hardening phases.
•The wear behaviour of various high entropy alloys up to 900 °C is analysed.•Wear rates of high entropy alloys decreases with increasing temperature.•High wear resistance of AlCoCrFeNi due to alumina scale and σ-phase precipitation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This paper reports the discovery of novel copper-based bulk metallic glasses free of group IV transition metals (Zr, Hf and Ti) in the Ca–Cu–Mg ternary system. Alloys of compositions ranging from ...Cu-33–55
at.%, Mg-18–36
at.% and Ca-18–36
at.%, located far from eutectic reactions, were found to exhibit high glass-forming ability (up to 8
mm using conventional copper mold casting), high hardness (up to 328
H
V) and low densities (2.9–4.0
g/cm
3).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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