High Glass-forming Ability Research Articles

On the thermodynamics and its connection to structure in the Pt-Pd-Cu-Ni-P bulk metallic glass forming system

Contrary to basic hard sphere structure models, recent studies revealed, significant structural differences between Pt-Cu-Ni-P and Pd-Cu-Ni-P metallic glass-forming liquids with the same stoichiometry. To cover the compositional space between both systems, platinum is subsequently replaced by palladium in the composition (Pt/Pd)42.5Cu27Ni9.5P21. For this systematic set of alloys, the thermodynamic properties, such as isobaric heat capacity, enthalpy and Gibbs free energy are assessed. A systematic drop of the Gibbs free energy difference between crystal and liquid, providing a lower estimate of the driving force for crystallization was observed, underlining the high glass-forming ability of the Pd-rich systems. Contrary to kinetic fragility data, a change of the thermodynamic fragility can be observed, drawing the picture of an increasing thermodynamically strong behavior with rising Pd-content. Further, the temperature induced changes of the total structure factors S(Q) were monitored using high-energy synchrotron X-ray diffraction. Focus was laid on the changes on the medium-range length scale, by analyzing changes of the first sharp diffraction peak. Here a good correlation of the changes in peak-width and the thermodynamic fragility was found. From the determination of the excess enthalpy, large amounts of residual enthalpy in the glassy state were observed for the Pt-rich alloys, supporting the increased ductility of these alloys. The current findings further carve out the different roles of the topologically similar Pt and Pd in the Pt/Pd-Cu-Ni-P alloy system and how the change of the structural motifs on the medium range order is influencing thermal properties such as enthalpy and heat capacity.

The effects of tantalum addition on the glass forming ability, thermal stability, and mechanical properties of Ni-Co-W-B bulk metallic glasses

The effects of Ta substitution for Ni and Co on the glass forming ability (GFA), thermal stability, and mechanical properties of (Ni0.592Co0.408)61.3-xTaxW23.7B15 (x=0-10) bulk metallic glasses were studied by differential thermal calorimetry (DSC), X-ray diffractometry (XRD), microhardness and compressive tests. Tantalum additions up to 8 at.% increases the GFA. The alloy containing 8 at.% Ta has the highest GFA and its critical thickness was determined to be 1.5 mm. It is also determined that the thermal and mechanical properties of the alloys improve with tantalum additions. The glass transition temperature increases from 854 K in (Ni0.592Co0.408)61.3W23.7B15 alloy to 971 K in (Ni0.592Co0.408)51.3Ta10W23.7B15 alloy. Also, microhardness increases from 1151 Hv for (Ni0.592Co0.408)61.3W23.7B15 alloy to 1262 Hv for (Ni0.592Co0.408)51.3Ta10W23.7B15 alloy. The compressive strength and elastic modulus of 8 at.% Ta containing alloy are 4.2 GPa and 204 GPa, respectively.

Toxic elements-free low-cost Ti-Fe-Si metallic glass biomaterial developed by mechanical alloying

Ti-Fe-Si systems that are free of toxic elements and have high glass-forming abilities are considered to be theoretically ideal biomaterials. Currently, Ti-Fe-Si amorphous alloy production by rapid solidification processing (RSP) is limited to strips, which restricts its size. In order to eliminate this size restriction, this study developed Ti-Fe-Si amorphous alloy powder for the first time using mechanical alloying (MA), thereby laying a foundation for its subsequent bulk preparation by the consolidation process. Furthermore, the effects of the big-to-small grinding balls weight ratio (BSR), the ball-to-powder weight ratio (BPR), and the milling time during MA on the amorphous transition of samples were systematically investigated. This work provides a new avenue to use Ti-Fe-Si metallic glass in medical devices.

Formation and properties of biocompatible Ti-based bulk metallic glasses in the Ti–Cu–Zr–Fe–Sn–Si–Ag system

The Ni-free Ti-based bulk metallic glasses (BMGs) with high glass-forming ability (GFA) can be synthesized in the (Ti, Cu, Zr)92.5Fe2.5Sn2Si1Ag2 alloy system over a wide composition range by copper-mold casting. Especially, the Ti48Cu37Zr7.5Fe2.5Sn2Si1Ag2 glassy alloy can form the BMG rod with a diameter up to 6 mm and showed a high compressive strength of ~ 2.05 GPa, elastic modulus of ~ 100 GPa, and microhardness of ~ 571 Hv. The Ti-based BMGs presented good bio-corrosion resistance in a simulated physiological environment attributed to the formation of Ti-, Zr-, Si-, and Fe-enriched passive films. The biocompatibility of the Ti-based glassy alloys was systematically investigated by both indirect cytotoxicity test and direct cell-culture experiments. The Ti-based BMG extracts had no cytotoxic effects on the proliferation of the cells. The good cell adhesion, proliferation, differentiation, and mineralization of bone-forming MC3T3-E1 pre-osteoblasts on the BMGs were parallel to those on the Ti–6Al–4V alloy. These results manifested that the present Ti-based BMGs are promising candidates as biomaterials.

The Effect of Mo Addition on Electrocatalytic Activity and Stability of Fe-Co-P-C Metallic Glasses for Hydrogen Evolution

Transition metals and alloys are expected to act as electrocatalysts for water splitting. Herein, we designed novel Fe-based metallic glasses by tuning the amount of Mo alloying. The prepared Mo-alloyed glassy ribbons substantially improved electrocatalytic activity for hydrogen evolution, with the optimal sample having an over-potential of 90 mV at a current density of 10 mA cm−2 in an acidic solution. The Mo-alloyed glasses presented here are the most efficient electrocatalysts to date among all known non-noble metallic glasses. In addition, we discovered that the Mo-dependent electrocatalytic activity of the studied alloys correlated closely with their glass-forming ability. Therefore, the superior electrocatalytic properties and high glass-forming ability of the present glasses are presumed to simultaneously originate from the intrinsic amorphous structure induced by tuning the Mo content. The results not only demonstrate the excellent electrocatalytic properties of Mo-alloyed metallic glasses as low-cost electrocatalysts for practical use, but also provide new mechanistic evidence for the electrocatalytic activity of amorphous metals.

Hafnium based metallic glasses with high density and high glass-forming ability

Metallic glasses (MGs) are advanced alloys possessing an amorphous structure and a host of properties (e.g., theoretical-limit-approaching strength) far superior to conventional crystalline metals/alloys. Hafnium-based MGs (HBMGs) have the additional advantage of high density, desirable for critical applications such as kinetic energy penetrators. HBMGs have still limited glass-forming ability (GFA), with a critical casting diameter/thickness (Dc) ≤10 mm, beyond which crystallization will occur. We report our discovery of two HBMGs, Hf40Zr9Cu31Ni8Al12 and Hf43Zr4Cu31.25Ni9.75Al12 possessing a Dc of 18 mm which nearly doubles the current record and enables notably bigger products and easier manufacturing/processing of HBMGs. Both alloys possess a density above 10.2 g/cm3, higher than most MGs based on other elements (e.g., Fe, Cu). They also stand out from most other MGs with a high Trg>0.61, high γ-parameter>0.42 and high atomic packing efficiency>0.8. We also report their thermal and mechanical properties and discuss the factors that may have contributed to their exceptional GFA.

Tribological behaviors of high-hardness Co-based amorphous coatings fabricated by laser cladding

Co-based metallic glasses with ultrahigh strength and high microhardness are regarded as ideal surface-coating materials to significantly improve hardness and wear resistance of substrate materials. In this paper, a Co-based amorphous powder with high glass-forming ability was prepared by gas-atomization technique. Then a large-area Co-based amorphous coating was fabricated from the powder by laser cladding technology. The effects of different laser parameters (i.e., laser scanning speed and operating voltage) on glass formation of the amorphous coating were investigated. Furthermore, the thermal properties, microhardness and wear resistance of the amorphous coating produced with an optimal laser parameter were evaluated. The results indicate that the Co-based amorphous cladding layer exhibits extremely high microhardness of ~14.9 GPa, which can significantly improve the wear resistance of the substrate. A complex wear-failure mechanism of the Co-based coating is clarified as a mixture role of abrasive- & fatigue-wear, oxidation wear and adhesive wear proofed by microstructural and element-distribution analysis of various worn surface.

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.

Glass-forming ability of Ni-Zr-Al alloys: the interplay of thermodynamic and geometric factors

ABSTRACT Despite decades of intensive rehearses, we still lack robust and physically clear methods to discover new metallic alloys with high glass-forming ability (GFA). Different empirical criteria proposed to estimate GFA have limited applicability. Here we address the impact of thermodynamic and geometric factors on GFA of Ni-Zr-Al alloys. Using the ideal associated solution model, we calculated the Gibbs energy and the mixing enthalpy of the system and compared the results with available experimental and theoretical data. The results show that the model used is a good approximation for calculating the thermodynamic properties of liquid alloys if both binary and ternary compounds are explicitly taken into account. However, we conclude that it is hardly possible to address GFA of Ni-Zr-Al alloys using only thermodynamic properties. We test a few different criteria, proposed in the literature, and show that they also fail to explain GFA in the system. Then, we propose new parameters based on Gibbs mixing energy and effective difference in atomic radii, which allows localising the composition domain corresponding to the best GFA in Ni-Zr-Al alloys. Our findings open up the prospects to develop reliable theoretical methods for discovering new metallic glasses.

Prediction and optimization of bulk metallic glass-forming compositions in Zr-Ni-Cu-Al system by thermodynamic modeling

The search for new criteria to predict glass-forming ability (GFA) in multicomponent metallic alloys is an important task from both fundamental and practical points of view. The decades of research have suggested that both thermodynamic and geometric factors contribute essentially to GFA of the alloys. Recently, P HS and P HSS parameters, which combine the enthalpy of chemical mixing, mismatch entropy, and configurational entropy, have been proposed and proved as successful criteria for the prediction of the GFA in several metallic glasses. Here we apply the thermodynamic modeling technique based on the ideal associated solution model to study GFA in (Ni 0.11 Cu 0.19 Zr 0.70 ) 1-x -Al x , (Ni 0.17 Zr 0.55 Cu 0.28 ) 1-x -Al x alloys with high Zr content. Our calculations reveal a clear correlation between P HS , P HSS parameters, and GFA in Ni-Zr-Cu-Al alloys for which bulk metallic glasses were experimentally fabricated. Based on the calculations, we predict that (Ni 0.17 Zr 0.55 Cu 0.28 ) 1-x -Al x alloys at x (Al) ≤ 0.2 possess high GFA.

Significant plasticity and atomic-scale deformation mechanism of high glass-forming Zr-Cu-Ni-Ti-Al bulk glassy alloys

The authors report a series of monolithic Zr(65.4-x)Cu(12+x)Ni9.6Ti6Al7 (x = 0, 3, 6, 9 at.%) bulk glassy alloys with significant room-temperature plasticity and high glass-forming ability (GFA). Upon substitution of Cu for Zr, the GFA of glassy alloys is gradually increased, and the alloy possesses a critical casting size up to 10 mm when x=9. On the contrary, the plasticity is evidently increased with decreasing of Cu content in the glassy alloys, and the alloy exhibits the best plastic strain of 29.6% when x=0. Theoretical calculations indicate that the small differences in atomic sizes and atomic affinity among constituent elements should be necessary before pronounced plastic deformation can occur.

Icosahedral clusters in Cu100-xZrx (x=32,34,36,38.2,40 at.%) metallic glasses near the peak of glass-forming ability (x=36): A balance between population and encaging strength

Understanding the origin of glass-forming ability (GFA) is important for the discovery or development of new metallic glasses (MGs). It is well known that the GFA in Cu–Zr binary MGs is sensitive to the composition and possesses a peak around Cu64Zr36 (at.%). The reason for this, however, is still not fully understood due to the complexity of the physics behind glass formation. Here, we use molecular dynamics simulations and statistics to study the structure and particularly the atomic energy state of the supercooled liquid and glass phases in the Cu100-xZrx (x = 32, 34, 36, 38.2, 40 at.%) alloy series. We show that the shell atoms of icosahedral clusters (the most dominant cluster type) in all these alloys have significantly lower (by > 1 eV/atom) potential energy than the core atoms. With rising Zr-content, the core–shell energy difference of the icosahedral clusters increases, making these clusters more strongly encaged and harder to break before or during crystallization. This effect counteracts the decrease in the population of the icosahedral clusters that has been noticed in previous studies. The net result of the interplay between these two factors can be represented by the product of the fraction of icosahedral shell-atoms and the core-shell energy difference, which exhibits a maximum at 36% Zr where the highest GFA has been observed. These findings provide new insights into the origin and peaking behavior of the GFA in this important binary bulk MG system, which could facilitate the search for the best glass-forming compositions in other alloy systems.

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.

Ti-Cu-Zr-Fe-Sn-Si-Ag-Pd Bulk Metallic Glasses with Potential for Biomedical Applications

Ti47Cu38−xZr7.5Fe2.5Sn2Si1Ag2Pdx (x = 1, 2, 3, and 4 atomic percent, at. pct) bulk metallic glasses (BMGs) with potential for biomedical applications were fabricated by copper-mold casting. The Ti-based BMGs exhibited high glass-forming ability (GFA) with critical diameters of 4 to 5 mm and a supercooled liquid region over 50 K, though the high contents of Pd slightly decreased the GFA. The additions of 2 and 3 at. pct Pd benefited the improvement of plasticity, and the resultant BMGs showed the relatively low Young’s modulus of about 100 GPa, high compressive strengths of 2174 to 2340 MPa, and compressive plastic strain of around 4 pct. The addition of Pd also decreased the passive current density and increased the pitting potential of the Ti-based BMGs in the Hank’s solution, leading to the enhanced bio-corrosion resistance of the BMGs. Furthermore, the cell adhesion, viability, and proliferation behaviors revealed that the present Ti-based BMGs possess as good biocompatibility as that of the Ti-6Al-4V alloy. These results demonstrated the potential of the Ti-Cu-Zr-Fe-Sn-Si-Ag-Pd BMGs as biomedical materials.

Balancing benefits of strength, plasticity and glass-forming ability in Co-based metallic glasses

Development of advanced metals materials with ultrahigh strength, large plasticity and high thermostability is one of the most attractive aims for materials researchers. Co-based bulk metallic glasses (BMGs) with the highest strength (up to 6 GPa) and special strength (up to 650 Nm/g) among all of metals materials so far we known have received extensive attentions. In this paper, a family of Co-Ta-B-Si BMGs with high glass-transition temperature (above 870 K), large compressive plasticity (up to 6.4 %) and high strength (above 5.5 GPa), and high glass-forming ability (the critical diameter, Dc: up to 4 mm) was developed by accurately tuning metalloid element contents of Si and B in the parental alloy of Co55Ta10B35. The changes of glass formation and plasticity caused by the adjustment of the constituent metalloid elements were evaluated by the combination of experimental and calculated results. The reason for the significant improvement of plastic deformation is revealed by the analysis of the self-organization behaviors of high-density shear bands.

Glass-Forming Ability and Thermal Properties of Al70Fe12.5V12.5X5(X = Zr, Nb, Ni) Amorphous Alloys via Minor Alloying Additions.

The Al70Fe12.5V12.5Ni5, Al70Fe12.5V12.5Zr5 and Al70Fe12.5V12.5Nb5 alloys were prepared via mechanical alloying. The influence of Zr, Nb or Ni addition on the glass-forming ability of Al-Fe-V amorphous alloys have been investigated. The structure of Al70Fe12.5V12.5Ni5 was amorphous and Al70Fe12.5V12.5Zr5 was not completely amorphous by transmission electron microscopy, selected area electron diffraction and differential scanning calorimetry. Different criteria were used to evaluate the influence of the addition of alloy elements on the Glass-forming ability. The Al70Fe12.5V12.5Ni5 amorphous alloys exhibits higher glass-forming ability and activation energies of crystallization. Comparison of the effective atomic size ratio and mixture enthalpy on the glass-forming ability of these amorphous alloys demonstrates that the effective atomic size ratio value becomes more significant than the values of mixture enthalpy.

Revealing the univariate effect of structural order on the oxidation of ternary alloys: Amorphous vs. crystalline Cu–Zr–Al alloys

A comparative oxidation study of homogeneous amorphous and crystalline Cu28Zr51Al21 alloys is presented to reveal the univariate role of structural order on the oxidation behavior of multi-component alloys. Amorphous Cu–Zr–Al is confirmed much more oxidation-resistant than crystalline Cu–Zr–Al. Preferential oxidation of Zr and Al occurs in both alloys, resulting in an amorphous Zr–Al–O layer and a Cu-enriched region. Cu-enrichment in the crystalline alloy causes Cu9Al4 nanocrystals embedded in the oxide. However, the Cu-enriched region in the amorphous alloy remains amorphous because of its high glass-forming ability. Findings provide design strategies for achieving highly oxidation-resistant alloys.

Ultrafine shape memory alloys synthesized using a metastable metallic glass precursor with polymorphic crystallization

Metallic glasses have been considered as a precursor for developing nano- or ultrafine-structured alloys based on its crystallization behavior at large undercooled liquid state. However, the multicomponent system, requiring high glass-forming ability, makes it difficult to control the crystallization mechanism, and leads to the formation of brittle intermetallic compounds during crystallization. Here, we present an intermetallic-type metallic glass precursor designed via thermodynamic and physical considerations. The metallic glass precursor polymorphically crystallized into ultrafine-structured single-phase shape memory alloy. The crystallization kinetics and final grain-size strongly depend on isothermal annealing temperatures. The shape memory alloys fabricated using the metallic glass precursor revealed excellent superelastic and shape memory effects, which was affected by the critical stress for martensitic transformation depending on the grain size. Our approach and discovery provide a feasibility of the simple fabrication processing for ultrafine-structured shape memory alloys by one-step heat-treatment technique including thermoplastic forming of metallic glass precursor.

Fatigue Behavior of Zr58Cu15.46Ni12.74Al10.34Nb2.76Y0.5 Bulk Metallic Glass Fabricated by Industrial-Grade Zirconium Raw Material

In this work, the fatigue behavior of a low-cost Zr58Cu15.46Ni12.74Al10.34Nb2.76Y0.5 (at%) bulk metallic glass (BMG) fabricated by industrial-grade Zirconium raw material was investigated under three-point bending loading mode. X-ray, fatigue tests under different stress amplitude and fatigue fractography were conducted in order to characterize the amorphous structure, fatigue stress-life (S-N) curve and fracture mechanism, respectively. It is found that the X-ray diffraction (XRD) result showed a fully amorphous structure due to high glass-forming ability, cracks initiated from inclusions near the rectangular corners at tensile surfaces and the fatigue endurance limit (~168 MPa) and fatigue ratio (~0.13) termed as fatigue endurance limit divided by ultimate tensile strength in stress amplitude were comparable to the similar BMG prepared by high pure raw materials.

Thermal and Magnetic Properties of Ternary Fe-B-C and Quaternary Fe-B-C-Si Alloys with High Glass-Forming Ability and High Magnetization

The thermal and magnetic properties of the ternary Fe-B-C and quaternary Fe-B-C-Si amorphous alloys have been investigated. It has been discovered that the ternary Fe-B-C amorphous alloys with compositions close to Fe79.3B14.3C6.4 exhibit a glass transition prior to crystallization on heating. The alloys also have high mass magnetization of 176–178 A m2/kg at room temperature. In addition, the glass-forming ability (GFA) of the alloys is significantly enhanced by the addition of 4 at% Si while maintaining high magnetization of approximately 170 A m2/kg at room temperature. In was found that the Fe23(B, C)6 phase (Cr23C6-type) is formed during crystallization of the quaternary Fe-B-C-Si alloys with the large GFA. It was also confirmed that the amorphous powders of Fe-Cr-B-C-Si alloys could be produced by a conventional water atomization method and exhibit the low core losses of 305–362 kW/m3 at 100 kHz and 100 mT. The quaternary Fe-B-C-Si amorphous alloys with high GFA, high magnetization and low core losses are suitable for a core material of various magnetic components.