Low Glass-forming Ability Research Articles

Atomic and Electronic Structure in MgO-SiO2.

Understanding disordered structure is difficult due to insufficient information in experimental data. Here, we overcome this issue by using a combination of diffraction and simulation to investigate oxygen packing and network topology in glassy (g-) and liquid (l-) MgO-SiO2 based on a comparison with the crystalline topology. We find that packing of oxygen atoms in Mg2SiO4 is larger than that in MgSiO3, and that of the glasses is larger than that of the liquids. Moreover, topological analysis suggests that topological similarity between crystalline (c)- and g-(l-) Mg2SiO4 is the signature of low glass-forming ability (GFA), and high GFA g-(l-) MgSiO3 shows a unique glass topology, which is different from c-MgSiO3. We also find that the lowest unoccupied molecular orbital (LUMO) is a free electron-like state at a void site of magnesium atom arising from decreased oxygen coordination, which is far away from crystalline oxides in which LUMO is occupied by oxygen's 3s orbital state in g- and l-MgO-SiO2, suggesting that electronic structure does not play an important role to determine GFA. We finally concluded the GFA of MgO-SiO2 binary is dominated by the atomic structure in terms of network topology.

Machine learning-guided exploration and experimental assessment of unreported compositions in the quaternary Ti-Zr-Cu-Pd biocompatible metallic glass system

Due to their outstanding elastic limit, biocompatible Ti-based bulk metallic glasses (BMGs) are candidate materials to decrease the size of medical implants and therefore reduce their invasiveness. However, the practical use of classical Ti-BMGs in medical applications is in part hindered by their high copper content: more effort is thus required to design low-copper Ti-BMGs. In this work, in line with current rise in AI-driven tools, machine learning (ML) approaches, a neural-network ML model is used to explore the glass-forming ability (GFA) of unreported low-copper compositions within the biocompatible Ti-Zr-Cu-Pd system. Two types of models are trained and compared: one based on the alloy composition only, and a second based on various features derived from the alloying elements. Contrary to expectation, the predictive power of both models in evaluating GFA is similar. The compositional space identified by ML as promising is experimentally assessed, finding unfortunately low GFA. These results indicate that the ML approach may be premature for specific composition tuning of amorphous metallic materials. We emphasise that the development of ML tools in GFA prediction requires an improvement of the dataset, in terms of homogeneity, size and GFA descriptors, which must be supported by increased reporting of high-quality experimental GFA measurements, both positive and negative. Statement of significanceBiocompatible Ti-based bulk metallic glasses (BMGs) are candidate materials for use in the next generation of minimally invasive dental implants where improved mechanical properties, such as high strength are required. Despite promising in vitro/vivo evaluations, implementation of alloys for practical applications is partly hindered by the presence of copper as the main alloying element. Recent studies have presented AI-guided and machine learning strategies as appealing approaches to understand and describe the glass forming ability (GFA) of BMG-forming compositions. In this work, we employ and evaluate the capacity of a machine-learning model to explore low-copper compositional spaces in the biocompatible Ti-Zr-Cu-Pd system. Our results highlight the limits of such a computational approach and suggest improvements for future designing routes.

Structural characterization of newly-developed Al79Ni5Fe5Y11 and Al79Ni11Fe5Y5 alloys with amorphous matrixes

The low glass-forming ability of aluminium-based metallic glasses significantly limits their development and preparation. This paper updates the current state of knowledge by presenting the results of structural studies of two newly-developed Al79Ni5Fe5Y11 and Al79Ni11Fe5Y5 alloys with a reduced aluminium content (< 80 at.%). The alloys were produced by conventional casting (ingots) and melt-spinning (ribbons). Structural characterization was carried out for bulk ingots first, and then for the melt-spun ribbons. The ingots possessed a multiphase crystalline structure, as confirmed by X-ray diffraction and scanning electron microscopy observations. The amorphous structure of the melt-spun ribbons was determined by X-ray diffraction and transmission electron microscopy. SEM observations and EDX element maps of the cross-section of melt-spun ribbons indicated a homogeneous elemental composition. Neutron diffraction revealed the presence of nanocrystals in the amorphous matrix of the melt-spun ribbons. DSC data of the melt-spun ribbons showed exothermic events corresponding to the first crystallization at temperatures of 408 °C and 387 °C for Al79Ni5Fe5Y11 and Al79Ni11Fe5Y5, respectively.

Glass transition temperatures of binary oxides from ab initio simulations

The glass transition temperatures of common binary oxides, including those with low glass-forming ability, are estimated using pair distribution functions (PDFs) from ab initio molecular dynamics simulations. The computed glass transition temperatures for good glass-formers such as silica (SiO2), germania (GeO2), and boron oxide (B2O3) are in agreement with measured values. These calculations are then used to compute the glass transition temperatures of alumina (Al2O3), tantala (Ta2O5), and telluria (TeO2), which are known to exhibit low glass-forming ability. For Al2O3 and Ta2O5, we also compute the simulated caloric curve from molecular dynamics simulations using two-body empirical force fields. Finally, we discuss the possibility of extracting the glass transition temperature by measuring the thermal broadening of the PDFs from scattering measurements.

A simplified rapid-quench multi-anvil technique.

We report a new rapid-quench technique for the Kawai-type multi-anvil press: several important improvements were made to our previous design. As a result, we are able to routinely quench melts with low glass-forming ability and form glasses. Owing to the use of 3D-printed parts to supply the coolant, the new designis easier to assemble and demonstrates better temperature stability and cooling rate. It was also found that the cooling rate is both pressure- and temperature-dependent. The cooling rate increases with increasing pressure from 6700°C/s at 1GPa to 8200°C/s at 5.5GPa and decreases with increasing temperature at a rate of 550°C s-1/100°C. Taking these dependencies into account, the new rapid-quench designproduces more than 15% higher cooling rate compared to the previous design. Moreover, enhancing coolant circulation, which was achieved by using tapered inner anvils with holes, additionally increases the cooling rate by about 4%. As the structure of the rapid-quench assembly differs dramatically from other existing designs, pressure calibration and temperature distribution in the experimental cell and sample capsule were determined for the first time. It was found that the first 0.6 MN of press load is not used to generate pressure due to the hard tungsten components in the assembly. At the current state-of-the-art, it is possible to routinely reach a pressure of 9GPa and a temperature of 2200K with the temperature variation not exceeding 70K within the sample capsule.

Structural investigations of Fe-Zr-Si-Cu metallic glass with low glass-forming ability produced in laser powder bed fusion technology

Fe-based metallic glasses (MG) have become the subject of extensive research in recent years due to their favorable mechanical and magnetic properties. In particular, the production of this type of materials in Laser Powder Bed Fusion (LPBF), also known as Selective Laser Melting (SLM) technology, is a kind of breakthrough, as it has become possible to produce elements of any shape. An important factor influencing the properties of the manufactured parts is their microstructure. For metallic glass Fe79Zr6Si14Cu1 with low glass-forming ability, produced in SLM technology, tests were carried out in the field of structural X-ray diffraction, Scanning Electron Microscopy, and Transmission Electron Microscopy. In addition, porosity analysis was compared with process parameters such as laser power and scanning speed. The paper shows that the fusion line comprises a solid solution α-Fe(Si) and low fraction of intermetallic Fe23Zr6 and FeZr2 phases. Furthermore, in the melt pool area, a nanometric α-Fe(Si) phase and an amorphous matrix was observed. The presented research results of the Fe79Zr6Si14Cu1 alloy produced for the first time in SLM technology will undoubtendly contribute to further optimization of parameters for elements produced in Additive Manufacturing technology using Fe-based MG.

General route to fabricate ultrafine metallic glass powders directly from their own crystalline states by localized pulsed electrical discharge atomization

Localized pulsed electrical discharge (PED) atomization is developed as a general route to fabricate ultrafine metallic glass powders with high purity and sphericity, which cannot be achieved by conventional techniques, like mechanical alloying, chemical reduction and water/gas atomization. The new atomization process starts with a localized melting on crystalline alloy surface by PED. During the melting process, multiple crystalline phases in the starting alloy are melted and then homogenized to form a uniform melted zone. Finally, the melted zone is atomized to produce ultrafine powders under the explosive force. The obtained particle size is mainly in the range of 1–10 μm. The results also show that it is easier to vitrify the produced powders for alloys with higher glass-forming ability (GFA). However, considering that the cooling rates achieved by PED atomization and melt-spinning technique are comparable, the GFA of the starting alloy will not play a determining role in the formation of glassy powders as long as it can guarantee the formation of glassy ribbons by melt-spinning technique. In this case, the ratio of melted zone size to crystalline phase size become the determining factor. The amorphization degree and compositional homogeneity can be improved by refining the starting alloy with low GFA. Besides, the experimental and simulation results both eliminate the possible Mo pollution from the tool electrode. This work will hopefully expand the applications of metallic glasses.

Understanding of crystallization behaviors in laser 3D printing of bulk metallic glasses

In 3D printing of bulk metallic glasses (BMGs) by selective laser melting (SLM), partial crystallization normally occurs in heat-affected zones (HAZs), which significantly deteriorates the properties of 3D-printed BMGs. To understand which factor dominates amorphous-to-crystalline conversion of 3D-printed BMGs, two representative BMG alloys with different glass forming ability (GFA), i.e., Zr55Cu30Ni5Al10 (named as Zr55 with high GFA) and Zr60.14Cu22.31Fe4.85Al9.7Ag3 (named as ZrAg with low GFA), were selected for SLM 3D printing, and their crystallization behaviors were comparatively studied. It is revealed that the 3D-printed ZrAg BMG with low GFA always possessed a higher amorphous phase content than the Zr55 BMG with a high GFA under different laser energy inputs. Thermal analysis and TEM observations revealed that crystal growth rate is the crucial factor for the resistance against amorphous-to-crystalline conversion in 3D-printed BMGs, as the ZrAg system exhibited much lower crystal growth rate although it has a lower GFA. The different crystal growth behavior of the two BMGs is associated with their different crystallization mechanisms: ZrAg BMG follows the mode of primary-type crystallization with multiple phases formation, leading to a low crystal growth rate, while Zr55 BMG follows the mode of polymorphous-type crystallization, which is characterized with formation of a simple crystalline phase, thus leading to a high crystal growth rate. The present work sheds light on the understanding of crystallization mechanism in 3D-printed BMGs and provides a guide for selection or design of BMG compositions for 3D printing.

Composition optimization of Al-Ni-Ti alloys based on glass-forming ability and preparation of amorphous coating with good wear resistance by plasma spray

Al-based alloys with compositions of Al 100-x-y Ni x Ti y (x = 5, 10, 15; y = 3, 6, 9) and Al 100-x-y Ni x Ti y (x = 10; y = 12, 15) were prepared by single-roller melt-spinning. To overcome the inability to measure the glass transition temperature , the amorphous content calculated from the X-ray diffraction pattern was used to evaluate glass-forming ability. The optimized composition with the highest glass-forming ability was Al 81 Ni 10 Ti 9 . The microhardness of the Al 81 Ni 10 Ti 9 ribbons increased first and then decreased when the ribbons were annealed at temperatures from 150 to 550 °C. Precipitation of α-Al nanocrystals improved the microhardness. There was no amorphous phase in the powders based on the optimized composition prepared by the atomization method, while the amorphous content of the coating obtained by plasma spray reached up to 49.76%. This was because the cooling rate in the spray process was at least two orders of magnitude higher than that in the gas atomization process. The coating had good wear resistance and the wear mechanisms were also analyzed. • A new method to evaluate the glass-forming ability (GFA) for alloys with low GFA; • A kind of Al-based amorphous coating was prepared by the plasma spray technology firstly; • The amorphous phase was not in the atomized powders but formed during the process of plasma spray; • Al-Ni-Ti amorphous coating possess good wear resistance and application prospects on surface engineering;

Relationship Between the Thermodynamic Parameters, Structure, and Anticorrosion Properties of Al-Zr-Ni-Fe-Y Alloys

The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y alloys are presented. To reduce the number of experiments, a thermodynamic approach was applied in which the entropy and Gibbs free energy of representative alloys were optimized. The low glass-forming ability of Al-Zr-Ni-Fe-Y alloy systems was related to the crystallization of the Al3Zr phase from the melt. The structural analysis showed that phases containing Ni and Fe, such as Al19Ni5Y3, Al10Fe2Y, and Al23Ni6Y4, played a key role in the formation of amorphous alloys. According to this, the simultaneous addition of Ni/Fe and Y is important to prevent the crystallization of Al-based alloys in the melt. The formation of an amorphous phase in Al80Zr5Ni5Fe5Y5 alloys and the complete amorphization of Al85Ni5Fe5Y5 alloys were responsible for the high corrosion resistance compared with fully crystalline alloys. Moreover, the addition of Y had a significant impact on the anticorrosion properties. The XPS results showed that the alloys tended to form a passive Al2O3 and Y2O3 layer on the surface.

Surface vitrification of iron and FeCuNbSiB alloy irradiated by intense pulsed ion beam

Intense pulsed ion beam (IPIB) is an emerging flash heat source for surface modification of metal. In IPIB treatment, the formation of amorphous phase is always considered as a significant mechanism to modify and improve the surface properties of target, due to the excellent mechanical performance of amorphous alloy. Thus, the understanding of surface vitrification process and its conditions induced by IPIB irradiation is of great value for its application. In this work, pure iron and FeCuNbSiB alloy were chosen as target for investigation in term of the difference of their glass forming ability (GFA). XRD results showed that the measurable amorphous layer cannot be formed in the surface of both of these two alloys after IPIB irradiation. Thermal field and solute diffusion were studied using the finite element method. It is indicated that during the IPIB irradiation, the molten surface layer of FeCuNbSiB alloy is heterogeneous, and thus it has much lower GFA than the Fe-Cu-Nb-Si-B mixed system. It is proposed that the sufficient mixture of elements in the molten surface layer is indispensable for surface vitrification. In addition, the formation of craters and cracks on the surface will be harmful to form amorphous layer.

Effect of minor Si additions and cooling rate on the phase formation and properties of glass former Ni57Nb33Zr5Co5 alloy

Ni57Nb33Zr5Co5 metallic glass is a promising candidate to be used as bipolar plates in Proton Exchange Membrane Fuel Cells. Nevertheless, this alloy presents a low glass-forming ability (GFA) and a relatively low supercooled liquid stability. A method well-known to improve the GFA of metallic glasses is via minor additions of alloying elements with a large difference in size and negative enthalpy of mixing relative to the elements in the glass. Using this approach, Si was identified to be a potentially good candidate to improve the GFA of the Ni57Nb33Zr5Co5. The aim of this work was to investigate the effect of Si additions and cooling rate on the formation and properties of this alloy. Ribbons and wedge shape samples of(Ni57Nb33Zr5Co5)100-xSix (x = 0.5, 1, 2 and 3 at.%) were prepared by melt spinning and suction casting, respectively, and characterized by X-ray diffraction, optical and scanning electron microscopy, differential scanning calorimetry and microhardness. The results show the addition of Si increases the supercooled region up to 84% mainly because of a significant decrease in the glass transition temperature but the additions do not improve the GFA of the Ni57Nb33Zr5Co5. The wedge samples showed that the critical diameter for amorphization is below 1 mm thickness and for larger sections, eutectic colonies of NiNb and Ni3Nb form together with primary Ni3Nb. It was observed that the addition of Si favors the formation of this primary phase, which increases in amount and size. High hardness values around 1150 HV were measured for regions with a fine eutectic structure and low amount of the primary phase.

Recent Topics on the Structure and Crystallization of Al-based Glassy Alloys

Al-based glassy alloys (metallic glasses) have been of great scientific and technological interest as a high specific strength and high corrosion resistant materials. However, the low glass-forming ability (GFA) is still a choke point that greatly influences the applications. In order to further comprehend the glass formation mechanism and investigate the possibility of enhancing the GFA, it is important to obtain the definite information on the atomic scale glassy structures in correlation with properties and to study the composition dependence of crystallization and properties of Al-based metallic glasses. The purpose of this paper is to summarize the structure characteristics and crystallization behavior in conjunction with alloy component in Al-based metallic glasses and to investigate the possibility of synthesizing an Al-based bulk metallic glass with better engineering performances. This may assist to learn the structural features systematically and understand the development and current status for Al-based metallic glasses.

New approach to amorphization of alloys with low glass forming ability via selective laser melting

The paper presents a new approach to selective laser melting (SLM) of alloys with low glass-forming ability and the basics of microstructure evolution during SLM of iron-based metallic glasses. After extensive parameters optimization, a novel scanning strategy, involving two-step melting, comprising preliminary laser melting, followed by short-pulse amorphization, has been introduced to maximize the glassy phase fraction and ensure good magnetic properties. Single melted samples show poor amorphization with well separated amorphous regions and coercivity of 1032 A/m. Second melting increased the glassy phase content by over an order of magnitude - up to 89.6% and reduced coercive force over four-times to 238 A/m. X-ray diffractions show significant difference between, arising from melt, disordered Fe(Si) phase and devitrified, ordered Fe3Si. Coexistence of those phases has been shown in heat affected zone by electron diffraction. Beneficial effect of the novel remelting strategy has been explained on the basis of restricted crystallization in heat-affected zone and reduction of sample overheating, by application of the Point-Random strategy.

Brazing method to join a novel Cu54Ni6Zr22Ti18 bulk metallic glass to carbon steel

ABSTRACTThis study joined a novel Cu-based bulk metallic glass (BMG) to carbon steel using a brazing process. Cu54Ni6Zr22Ti18 BMG was brazed to SS400 carbon steel using filler metal at 713 K under a compressive stress of 15 MPa for 3 min. Considering the relatively low glass-forming ability, pure Zn and Zn–Ag–Al filler metals were selected to suppress the crystallisation during a reheating thermal cycle. A sound bonding interface without notable chemical diffusion was obtained using the suggested brazing method, particularly with the Zn–Ag–Al filler. This gave rise to considerable improvement in shear bonding strength, from 9 to 45 MPa, when replacing the Zn filler with the Zn–Ag–Al filler. The present method also induced no marked change in phase composition of the BMG due to the low bonding temperature and short bonding time. Slight variations in glass transition temperature and crystallisation temperature would result from a thermal annealing effect.

Structural properties and energy analysis of ZrxCu92−xAl8 ternary metallic glasses

In this work, classic molecular dynamics simulations were employed to study ZrxCu92−xAl8 (x=55, 60, 65, and 70) ternary alloys. When Cu atoms were gradually replaced by Zr atoms, the local atomic structural evolution and energy landscape were analyzed. Pair distribution functions were used to characterize the structural features. The results showed that Zr-Al, Zr-Cu and Cu-Al atom pairs showed a strong short range order (SRO) within the first shell and they exhibited a weak sensitivity to atomic concentrations while Zr-Zr and Cu-Cu atom pairs presented a strong sensitivity to atomic concentrations. The analyses of the coordination number and coordination polyhedra indicated that substituting Zr atoms for Cu atoms led to the reduction of high coordination polyhedra and precluded the formation of the icosahedral structure, resulting in a more loosely packed atomic structure of the metallic glass. Finally, the energy landscape revealed that, with the increase of Zr composition and the decrease of Cu composition, the energy distribution of the Zr-centered clusters shifted towards a higher energy significantly and this originated from the increase of the number of Zr-Zr atom pairs and the growth of the Zr-Zr atom pair energy. The simulation results revealed that, from both consideration of the structure and energy distributions, the high Zr content Zr-Cu-Al metallic glasses were composed of more weakly bonded regions and packed more loosely, in line with the experimental results that the high Zr content glassy alloys exhibited high plasticity and low glass-forming ability.

Glass forming ability of (Hf,Cr)[sbnd]Co[sbnd]B alloys: Computational and experimental studies

The quantities describing glass forming ability (GFA) of (Hf,Cr)CoB system were calculated. Enthalpies of formation of amorphous state, solid solution and intermetallic phases were determined and discussed along with normalized mismatch entropy and glass forming ability parameter. All thermodynamic quantities were confronted with the experimental results of the structural and thermal analysis of Hf2−xCrxCo11B (0≤x≤2) melt-spun alloys. Much emphasis was put on the alloy of the composition 2:11:1 because of its possible application as a permanent magnet material. Formation enthalpy of Hf2Co11B amorphous alloy ΔHam=−20.6kJ/mol, being in agreement with other determined parameters, indicates moderate glass forming ability. With increasing Cr content ΔHam becomes less negative and for Cr2Co11B it reaches ΔHam=−0.5kJ/mol. Cr-rich alloys are believed to not form amorphous state, which was confirmed by experimental results. Formation of solid solution is preferred in the latter case. Low GFA of Cr-containing alloy is connected with similar atomic radii of Cr and Co and smaller interfacial enthalpy of CrCo than HfCo pair. Fully amorphous diffraction patterns were observed for the alloys with high Hf content (0≤x≤1), while formation of crystalline phases at the expense of amorphous state was shown for 1.5≤x≤2 and indirectly confirmed by density measurements. Higher thermal stability of Hf-rich alloys is consistent with their moderate GFA.

Poor glass-forming ability of Fe-based alloys: Its origin in high-temperature melt dynamics

The relatively poor glass-forming ability (GFA) of Fe-based alloys has limited the mass production of Fe-based bulk metallic glasses (MGs), and hence their applications. To clarify the origin of the low GFA of the Fe-based alloys, we investigate the dynamic behaviors of these alloy systems well above their respective liquidus temperatures. By using a torsional oscillating viscometer we have observed a dynamic transition, where the slope of the viscosity-temperature relation of the Fe-based metallic liquid increases upon cooling, and a viscosity hysteresis occurs between the heating and cooling processes. By using the concept of fluid cluster and supercooled liquid fragility in metallic liquids, it has been found that this dynamic transition makes the Fe-based supercooled liquids become more unstable, which leads to the poor GFA of Fe-based alloys. Further, it has been found that the degree of the dynamic transition relates to the different GFA among Fe-based alloys. By taking into account the thermodynamic effect accompanied with the dynamic transition in Fe-based melts, a possible scenario has been proposed from the aspect of the underlying structural evolution during cooling above the liquidus temperature.

On conditions of bulk and surface glass formation of metallic alloys

Abstract This work is done to analyze the effect of glass forming compounds and melt processing on bulk and surface glass formation. Key factors of glass formation of metallic alloys including structure-phase state of solid precursor (i.e. master-ingot, spun ribbon, powder, etc.) and its melt, conditions of cooling melt and its ability for deep undercooling are considered. A ratio of crystalline glass forming compounds in annealed best BMG compositions is considered to develop a strategy of searching new alloys. Surface glass formation at electro-spark deposition of precursors with high and low GFA used as consumable electrodes is studied. It found that surface glass formation is possible due to both weak and strong chemical interaction of an electrode and a substrate. The former is due to mass transfer of high glass forming ability (GFA) precursor onto metallic substrate with local “drop-by-drop” anode melting stimulated by electric discharge and needs no chemical interaction. The latter goes with diffusion interaction between low GFA precursor and a metallic substrate by a local melting and it is other way to form amorphous surface layer. In both cases the solidification rate of molten drops by electro-spark deposition is enough to suppress crystallization and is compared to melt spinning.

Ternary Fe-B-C and quaternary Fe-B-C-Si amorphous alloys with glass transition and high magnetization

Abstract The ternary Fe-B-C amorphous alloys exhibit good soft magnetic properties and high saturation magnetization. The high magnetization is favorable to reduce the size of the magnetic devices. However, mass production of the Fe-B-C amorphous alloys is difficult due to their low glass-forming ability (GFA). In the present study, the various properties of the ternary Fe-B-C and quaternary Fe-B-C-Si amorphous alloys have been investigated. It has been discovered for the first time that some ternary Fe-B-C amorphous alloys with the Fe content close to that of the Cr 23 C 6 -type metastable Fe 23 (B, C) 6 phase exhibit a glass transition prior to crystallization on heating. The alloys with the glass transition also have high mass magnetization of 176–178 A m 2 /kg at room temperature in as as-quenched state. As a result of attempts to improve GFA by Si addition to the Fe-B-C alloys, it has been discovered that the quaternary (Fe 0.780 B 0.152 C 0.068 ) 96 Si 4 and (Fe 0.767 B 0.148 C 0.085 ) 96 Si 4 amorphous alloys exhibit the large GFA. The large GFA of the quaternary Fe-B-C-Si alloys enables to produce thick amorphous specimens with 120 μm in thickness and with high mass magnetization of approximately 170 A m 2 /kg at room temperature in as as-quenched state. The ternary Fe-B-C and quaternary Fe-B-C-Si amorphous alloys with high GFA as well as high magnetization are suitable for a core material of various magnetic components.