Crystallization of Co<Subscript>100-<Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>B<Subscript>10</Subscript>Si<Subscript>12</Subscript> amorphous metallic alloys

Alloys of Co_78-x Pt _x B₁₀Si₁₂ were produced using the melt-spin process in order to study the crystallization behavior and ensuing magnetic properties of the Co-Pt amorphous alloys as a function of the Pt content. We showed that when x>15, well below its stoichiometric composition, CoPt intermetallic compound crystallized in the amorphous alloy. Below this composition, the main crystallization product was Co with Pt dissolved in its lattice. The nucleation of CoPt greatly altered the crystallized microstructures and magnetic properties of the Co-Pt amorphous alloys during annealing. In spite of the nucleation of CoPt with its high magnetic anisotropy, the highest coercivity was obtained when x was 15, free of the CoPt grains. It was also concluded that the Pt addition, in general, triggered crystallization to occur at a progressively lower temperature.     

Effect of Au Content on Thermal Stability and Mechanical Properties of Au-Cu-Ag-Si Bulk Metallic Glasses

The thermal stability, glass-forming ability (GFA), and mechanical and electrical properties of Au-based Au _x Si₁₇Cu_75.5–x Ag_7.5 (x = 40 to 75.5 at. pct) metallic glasses were investigated. The glass transition temperature (T _g ) and crystallization temperature (T _x ) decreased with increasing Au content. The ultralow T _g values below 373 K (100 °C) were obtained for alloys with x = 55 to 75.5. The alloys with x = 45 to 70 exhibited a high stabilization of supercooled liquid and a high GFA, and the supercooled liquid region and critical sample diameter for glass formation were in the range of 31 K to 50 K and 2 to 5 mm, respectively. The compressive fracture strength (σ _c,f ), Young’s modulus (E), and Vicker’s hardness (H _v ) of the bulk metallic glasses (BMGs) decreased with increasing Au content. A linear correlation between Au concentration and the characteristic temperature, i.e., T _g and T _x , and mechanical properties, i.e., σ _c,f , E, and H _v , as well as electrical resistivity can be found in the BMGs, which will be helpful for the composition design of the desirable Au-based BMGs with tunable physical properties.     

Mechanical performance of the Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoCrCuFeNi high-entropy alloy system with multiprincipal elements

The Al _x CoCrCuFeNi alloys with multiprincipal elements (x=the aluminum content in molar ratio, from 0 to 3.0) were synthesized using a well-developed arc-melting and casting method, and their mechanical properties were investigated. These alloys exhibited promising mechanical properties, including excellent elevated-temperature strength and good wear resistance. With the addition of aluminum from x=0 to 3.0, the hardness of the alloys increased from HV 133 to 655, mainly attributed to the increased portion of strong bcc phase to ductile fcc phase, both of which were strengthened by the solid solution of aluminum atoms and the precipitation of nanophases. The alloys exhibited superior high-temperature strengths up to 800 °C, among which the Al_0.5CoCrCuFeNi alloy, especially, had enhanced plasticity and a large strain-hardening capacity. Moreover, the wear resistance of these alloys was similar to that of ferrous alloys at the same hardness level, while the alloys with lower hardness exhibited relatively higher resistance because of their large strain-hardening capacity.     

Phase transitions in the magnetic superconductor (Dy<Subscript>0.8</Subscript>Y<Subscript>0.2</Subscript>)Rh<Subscript>4</Subscript>B<Subscript>4</Subscript>

A new (Dy_0.8Y_0.2)Rh₄B₄ superconductor (the superconducting transition temperature is T _c ≈ 5.5 K), which has an inherent magnetic subsystem whose properties are determined by the crystal structure of the superconductor, is synthesized at a high pressure (∼8 GPa) and t ≈ 1800°. The magnetic sublattice of the (Dy_0.8Y_0.2)Rh₄B₄ compound is found to substantially affect its superconducting properties and, in a number of cases, to lead to their anomalous variations, namely, to the absence of the traditional Meissner effect and an anomalously abrupt increase in magnetic induction B _k2 (upper critical field) upon a transition of the magnetic subsystem into the antiferromagnetic state. Upon cooling from 250 to 1.6 K, the (Dy_0.8Y_0.2)Rh₄B₄ compound undergoes a number of phase transformations, namely, a paramagnet-ferrimagnet transition at a Curie temperature T _C ≈ 30 K, a superconducting transition at T _c ≈ 5.5 K against the background of a ferrimagnetic order, and a ferrimagnet-antiferromagnet transition (the Neel temperature is T _N ≈ 2.8 K) in the retained superconducting state.     

Wear resistance and high-temperature compression strength of Fcc CuCoNiCrAl<Subscript>0.5</Subscript>Fe alloy with boron addition

This study discusses the wear resistance and high-temperature compression strength of CuCoNiCrAl_0.5Fe alloy with various amounts of boron addition. Experiments show that within the atomic ratio of boron addition from x=0 to x=1.0 in CuCoNiCrAl_0.5FeB _x (referred to as B-0 to B-1.0 alloys), the alloys are of fcc structure with boride precipitation. The volume fraction of borides increases with increasing boron addition. The corresponding hardness increases from HV 232 to HV 736. Wear resistance and high-temperature compression strength are significantly enhanced by the formation of boride. The alloys with boride are less tough. The superior wear resistance of B-1.0 alloy, which is even better than SUJ2 wear-resistant steel, indicates that the CuCoNiCrAl_0.5FeB _x alloys have potential applications as ambient- and high-temperature mold, tool, and structural materials.     

Wettability of Mn<Subscript>x</Subscript>Si<Subscript>y</Subscript>O<Subscript>z</Subscript> by Liquid Zn-Al Alloys

The wettability of Mn_xSi_yO_z by liquid Zn-Al alloys was investigated to obtain basic information on the coating properties of high-strength steels with surface oxides in the hot-dip galvanizing process. In this study, the contact angles of liquid Zn-Al alloys (Al concentrations were 0.12 and 0.23 wt pct) on four different Mn_xSi_yO_z oxides, namely MnO, MnSiO₃, Mn₂SiO₄, and SiO₂, were measured with the dispensed drop method. The contact angle did not change across time. With an increasing Al concentration, the contact angle was slightly decreased for MnO and Mn₂SiO₄, but there was no change for MnSiO₃ and SiO₂. With an increasing SiO₂ content, the contact angle gradually increased by 54 wt pct to form MnSiO₃, and for pure SiO₂ substrate, the contact angle decreased again. Consequently, the MnSiO₃ substrate showed the worst wettability among the four tested oxide substrates.     

Stabilizing the L1<Subscript>2</Subscript> structure of Pt<Subscript>3</Subscript>Al(r) in the Pt-Al-Sc system

The Pt-Al system has high potential to act as alloy base for so-called refractory superalloys. Although the envisaged strengthening phase Pt₃Al(r) has favorable L1₂ crystal structure only at high temperatures, even small amounts of Sc stabilized L1₂ crystal structure at low temperature. Pt-Al-Sc alloys were arc melted, heat treated, and examined by means of scanning electron microscopy and X-ray diffraction (XRD). Pt₃Al_1−x Sc _x (r) forms a continuous phase field from the Al-rich side to the Sc-rich side of the Pt-Al-Sc ternary system. The absolute value of the lattice misfit between cubic Pt₃Al_1−x Sc _x (r) and the matrix decreases with increasing Sc content.     

Structural Transitions and Magnetic Properties of Ni<Subscript>50</Subscript>Mn<Subscript>36.7</Subscript>In<Subscript>13.3</Subscript> Particles with Amorphous-Like Phase

The high-energy ball-milling method was used for fabricating Ni₅₀Mn_36.7In_13.3 fine-sized particles. The as-melt polycrystalline Ni₅₀Mn_36.7In_13.3 alloy exhibits a 14 M modulated martensite structure at room temperature (RT). The atomic pair distribution function analysis together with the differential scanning calorimetry technique proved that the 14 M modulated martensite transformed to a metastable amorphous-like structure after ball milling for 8 hours. Annealing of the ball-milled particles with the amorphous-like phase first led to the crystallization to form a B2 structure at 523 K (250 °C), and then an ordered Heusler L2₁ structure (with a small tetragonal distortion) at 684 K (411 °C). The annealed particles undergo different structural transitions during cooling, tailored by the atomic arrangements of the high-temperature phase. Low-field thermomagnetization measurements show that the ball-milled particles with the amorphous-like structure or the atomically disordered crystalline structure exhibit a magnetic transition from the paramagnetic-like to the spin-glass state with decreasing temperature, whereas the crystalline particles with the ordered Heusler L2₁ structure present a ferromagnetic behavior with the Curie temperature T _c ≈ 310 K (37 °C).     

Thermodynamics of MnO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MnS Liquid Oxysulfide: Experimental and Thermodynamic Modeling

The activities of MnO and MnS in a MnO-SiO₂-Al₂O₃(or AlO_1.5)-MnS liquid oxysulfide solution were investigated by employing the gas/liquid/Pt-Mn alloy chemical equilibration technique under a controlled atmosphere at 1773 K (1500 °C). Also, the sulfide capacity, defined as C _S = (wt pct S)(pO₂/pS₂)^1/2, in MnO-SiO₂-Al₂O₃ slag with a dilute MnS concentration was obtained from the measured experimental data. As X _SiO2/(X _MnO + X _SiO2) in liquid oxysulfide increases, the activity coefficient of MnO decreases, while that of MnS first increases and then decreases. As X(AlO_1.5) in liquid oxysulfide increases, the activity coefficient of MnS increases, while no remarkable change is observed for the activity coefficient of MnO. The behavior of the activity coefficient of MnS was qualitatively analyzed by considering MnO + A _x S _y (SiS₂ or Al₂S₃) = MnS + A _x O _y (SiO₂ or Al₂O₃) reciprocal exchange reactions in the oxysulfide solution. The behavior was shown to be consistent with phase diagram data, namely, the MnS saturation boundary. Quantitative analysis of the activity coefficient of the oxysulfide solution was also carried out by employing the modified quasichemical model in the quadruplet approximation.     

Structure, Properties, and Glass Forming Ability of Melt-Spun Fe-Zr-B-Cu Alloys with Different Zr/B Ratios

Melt-spun ribbons of Fe_99–x–y Zr _x B _y Cu₁ alloys with x + y = 11 and x + y = 13 were prepared under similar experimental conditions and characterized for structure and soft magnetic properties. Substitution of Zr by B changes the structure of as-spun ribbons from completely amorphous to cellular bcc solid solution coexisting with the amorphous phase at intercellular regions and then to completely dendritic solid solution. The glass forming ability (GFA) of the Fe-Zr-B-Cu system, evaluated from thermodynamic properties such as enthalpy of mixing and mismatch entropy, is found to be in good agreement with the experimental observations. Annealing of all ribbons leads to the precipitation of nanocrystalline bcc α-Fe phase from both amorphous phase and already existing bcc solid solution. A window of alloy compositions that exhibit the best combination of soft magnetic properties (high saturation magnetization and low coercivity) was identified.     

Effect of Nb Concentration on Thermal Stability and Glass-Forming Ability of Soft Magnetic (Fe,Co)-Gd-Nb-B Glassy Alloys

Addition of a small amount of Nb to the (Fe,Co)-Gd-B glassy alloy in (Fe_0.9Co_0.1)_71.5−x Nb _x Gd_3.5B₂₅ increased the stabilization of supercooled liquid. The largest supercooled liquid region of 104 K was obtained for the x = 2 alloy. A distinct two-stage-like glass transition was observed with further incresing Nb content. The nanoscale (Fe,Co)₂₃B₆ phase precipitated in the glassy matrix after annealing, while the two-stage-like glass transition disappeared, indicating that the anomalous glass transition behavior originates from the exothermic reaction for the formation of the (Fe,Co)₂₃B₆ phase in the supercooled liquid region. The glass-forming ability (GFA) also increased by addition of Nb, leading to formation of the bulk glass form for the Nb-doped alloys. The best GFA with a diameter of over 3 mm was achieved for the x = 4 alloy. The (Fe,Co)-Gd-Nb-B glassy alloys exhibited good magnetic properties, i.e., rather high saturation magnetization of 0.81 to 1.22 T, low coercive force of 2.5 to 5.8 A/m, and low saturated magnetostriction of 9 to 19 × 10⁻⁶. In addition, the glassy alloys also possessed very high compressive fracture strength of 3842 to 3916 MPa and high Vickers hardness of 1025 to 1076.     

Microstructural Evolution and Mechanical Properties of Nanointermetallic Phase Dispersed Al<Subscript>65</Subscript>Cu<Subscript>20</Subscript>Ti<Subscript>15</Subscript> Amorphous Matrix Composite Synthesized by Mechanical Alloying and Hot Isostatic Pressing

The structure and mechanical properties of nanocrystalline intermetallic phase dispersed amorphous matrix composite prepared by hot isostatic pressing (HIP) of mechanically alloyed Al₆₅Cu₂₀Ti₁₅ amorphous powder in the temperature range 573 K to 873 K (300 °C to 600 °C) with 1.2 GPa pressure were studied. Phase identification by X-ray diffraction (XRD) and microstructural investigation by transmission electron microscopy confirmed that sintering in this temperature range led to partial crystallization of the amorphous powder. The microstructures of the consolidated composites were found to have nanocrystalline intermetallic precipitates of Al₅CuTi₂, Al₃Ti, AlCu, Al₂Cu, and Al₄Cu₉ dispersed in amorphous matrix. An optimum combination of density (3.73 Mg/m³), hardness (8.96 GPa), compressive strength (1650 MPa), shear strength (850 MPa), and Young’s modulus (182 GPa) were obtained in the composite hot isostatically pressed (“hipped”) at 773 K (500 °C). Furthermore, these results were compared with those from earlier studies based on conventional sintering (CCS), high pressure sintering (HPS), and pulse plasma sintering (PPS). HIP appears to be the most preferred process for achieving an optimum combination of density and mechanical properties in amorphous-nanocrystalline intermetallic composites at temperatures ≤773 K (500 °C), while HPS is most suited for bulk amorphous alloys. Both density and volume fraction of intermetallic dispersoids were found to influence the mechanical properties of the composites.     

On the fracture and fatigue properties of Mo-Mo<Subscript>3</Subscript>Si-Mo<Subscript>5</Subscript>SiB<Subscript>2</Subscript> refractory intermetallic alloys at ambient to elevated temperatures (25 °C to 1300 °C)

The need for structural materials with high-temperature strength and oxidation resistance coupled with adequate lower-temperature toughness for potential use at temperatures above ∼1000 °C has remained a persistent challenge in materials science. In this work, one promising class of intermetallic alloys is examined, namely, boron-containing molybdenum silicides, with compositions in the range Mo (bal), 12 to 17 at. pct Si, 8.5 at. pct B, processed using both ingot (I/M) and powder (P/M) metallurgy methods. Specifically, the oxidation (“pesting”), fracture toughness, and fatigue-crack propagation resistance of four such alloys, which consisted of ∼21 to 38 vol. pct α-Mo phase in an intermetallic matrix of Mo₃Si and Mo₅SiB₂ (T₂), were characterized at temperatures between 25 °C and 1300 °C. The boron additions were found to confer improved “pest” resistance (at 400 °C to 900 °C) as compared to unmodified molybdenum silicides, such as Mo₅Si₃. Moreover, although the fracture and fatigue properties of the finer-scale P/M alloys were only marginally better than those of MoSi₂, for the I/M processed microstructures with coarse distributions of the α-Mo phase, fracture toughness properties were far superior, rising from values above 7 MPa √m at ambient temperatures to almost 12 MPa √m at 1300 °C. Similarly, the fatigue-crack propagation resistance was significantly better than that of MoSi₂, with fatigue threshold values roughly 70 pct of the toughness, i.e., rising from over 5 MPa √m at 25 °C to ∼8 MPa √m at 1300 °C. These results, in particular, that the toughness and cyclic crack-growth resistance actually increased with increasing temperature, are discussed in terms of the salient mechanisms of toughening in Mo-Si-B alloys and the specific role of microstructure.     

Synthesis and Characterization of Lithium Borate Glasses Containing La<Subscript>2</Subscript>O<Subscript>3</Subscript>

The glass series with general formula 15 Li₂O–(85 − x) B₂O₃–x La₂O₃ was prepared. Electrical and optical properties of these glasses were studied. It is observed that the conductivity of these glasses decreases while density, glass transition temperature and refractive index increases with the addition of La₂O₃. Ion concentration of La³⁺ in glasses, polaron radius, field strength, molar refractivity and molar electronic polarizability were calculated. The absorption coefficient and direct optical band gaps are evaluated using the absorption edge calculations. The different factors that play a role for controlling the refractive indices such as electronic polarizability, field strength of cations and rigidity of glass structure are discussed in accordance with the obtained index data.     

High-Accuracy X-Ray Diffraction Analysis of Phase Evolution Sequence During Devitrification of Cu<Subscript>50</Subscript>Zr<Subscript>50</Subscript> Metallic Glass

Real-time high-energy X-ray diffraction (HEXRD) was used to investigate the crystallization kinetics and phase selection sequence for constant-heating-rate devitrification of fully amorphous Cu₅₀Zr₅₀, using heating rates from 10 K/min to 60 K/min (10 °C/min to 60 °C/min). In situ HEXRD patterns were obtained by the constant-rate heating of melt-spun ribbons under synchrotron radiation. High-accuracy phase identification and quantitative assessment of phase fraction evolution though the duration of the observed transformations were performed using a Rietveld refinement method. Results for 10 K/min (10 °C/min) heating show the apparent simultaneous formation of three phases, orthorhombic Cu₁₀Zr₇, tetragonal CuZr₂ (C11_b), and cubic CuZr (B2), at 706 K (433 °C), followed immediately by the dissolution of the CuZr (B2) phase upon continued heating to 789 K (516 °C). Continued heating results in reprecipitation of the CuZr (B2) phase at 1002 K (729 °C), with the material transforming completely to CuZr (B2) by 1045 K (772 °C). The Cu₅Zr₈ phase, previously reported to be a devitrification product in C₅₀Zr₅₀, was not observed in the present study.     

Infrared Brazing Fe<Subscript>3</Subscript>Al Using Ag-Based Filler Metals

The microstructural evolution and bonding shear strength of infrared brazed Fe₃Al using Ag and BAg-8 (72Ag-28Cu in wt pct) braze alloys have been studied. The Ag-rich phase alloyed with Al dominates the entire Ag brazed joints, and the shear strength is independent of the brazing time. The BAg-8 brazed joint contains Ag-Cu eutectic for all brazing conditions, and its shear strength increases slightly with increasing brazing time. The highest shear strength of 181 MPa is acquired from the joint infrared brazed at 1073 K (800 °C) for 600 seconds. A thin layer of Fe₃Al is identified at the interface between the brazed zone and the substrate for both braze alloys. An Al depletion zone in the Fe₃Al substrate next to the interfacial Fe₃Al is identified as the α-Fe phase. The dissolution of Al from the Fe₃Al substrate into the molten braze causes the formation of α-Fe in the Fe₃Al substrate.     

Oxidation Behavior of a Pd<Subscript>43</Subscript>Cu<Subscript>27</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> Bulk Metallic Glass and Foam in Dry Air

The oxidation behavior of both Pd₄₃Cu₂₇Ni₁₀P₂₀ bulk metallic glass (Pd4-BMG) and its amorphous foam containing 45 pct porosity (Pd4-AF) was investigated over the temperature range of 343 K (70 °C) to 623 K (350 °C) in dry air. The results showed that virtually no oxidation occurred in the Pd4-BMG at T < 523 K (250 °C), revealing the alloy’s favorable oxidation resistance in this temperature range. In addition, the oxidation kinetics at T ≥ 523 K (250 °C) followed a parabolic-rate law, and the parabolic-rate constants (k _p values) generally increased with temperature. It was found that the oxidation k _p values of the Pd4-AF are slightly lower than those of the Pd4-BMG, indicating that the porous structure contributes to improving the overall oxidation resistance. The scale formed on the alloys was composed exclusively of CuO at T ≥ 548 K (275 °C), whose thickness gradually increased with increasing temperature. In addition, the amorphous structure remained unchanged at T ≤ 548 K (275 °C), while a triplex-phase structure developed after the oxidation at higher temperatures, consisting of Pd₂Ni₂P, Cu₃P, and Pd₃P.     

Understanding the Effect of Oxygen on the Glass-Forming Ability of Zr55Cu55Al9Be9 Bulk Metallic Glass by ab initio Molecular Dynamics Simulations

Oxygen (O) is an inevitable impurity in bulk metallic glasses (BMGs) and its influence over the glass-forming ability (GFA) of BMGs is a longstanding controversy. The present ab initio molecular dynamics (AIMD) simulations indicate that the GFA decreases upon introducing 0.78 at. pct O in the amorphous Zr₅₅Cu₅₅Al₉Be₉ (at. pct), while examining the evolution of atomic configurations and kinetic properties in BMGs. This study includes a comprehensive analysis using pair correlation function (PCF), bond pair analysis (BPA), and Voronoi polyhedra construction. It is concluded that the incorporation of O leads to a decline in the closely packed icosahedral polyhedrons, where the atom O is coordinated with Be and Zr in the first nearest shell to form the O-centered clusters with enhanced ordering. Mean square displacement (MSD) analysis also shows that the trace O could induce remarkable acceleration of atomic mobility, therefore increasing crystallization tendency of the Zr₅₅Cu₅₅Al₉Be₉ alloy. The present results illuminate the role of O in the metallic glass-forming process and reveal the underlying role of O in the GFA of the Zr-Cu amorphous alloys.

     

The Thermal Stability of R<Subscript>3</Subscript>Pt<Subscript>4</Subscript> Compounds

Alloys of the rare earths R (including La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er) with platinum, having the composition R₃Pt₄, have been synthesized and investigated by X-ray diffraction (XRD) and differential thermal analysis (DTA). At temperatures above about 900 °C and below 250 °C, all the single phases R₃Pt₄ are formed, which crystallize with the same structure of the rhombohedral Pu₃Pd₄ type. Over the temperature range of about 250 °C to 900 °C, they occur at an eutectoid decomposition into RPt and RPt₂ compounds neighboring in the corresponding phase diagram, R₃Pt₄ → RPt + RPt₂. The stability of these phases R₃Pt₄ may be restricted to a radius ratio r _R/r _Pt range of 1.27 to 1.35.     

Microstructure characterization of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoCrCuFeNi high-entropy alloy system with multiprincipal elements

A new approach for the design of alloy systems with multiprincipal elements is presented in this research. The Al _x CoCrCuFeNi alloys with different aluminum contents (i.e., x values in molar ratio, x=0 to 3.0) were synthesized using a well-developed arc-melting and casting method. These alloys possessed simple fcc/bcc structures, and their phase diagram was predicted by microstructure characterization and differential thermal analyses. With little aluminum addition, the alloys were composed of a simple fcc solid-solution structure. As the aluminum content reached x=0.8, a bcc structure appeared and constructed with mixed fcc and bcc eutectic phases. Spinodal decomposition occurred further on when the aluminum contents were higher than x=1.0, leading to the formation of modulated plate structures. A single ordered bcc structure was obtained for aluminum contents larger than x=2.8. The effects of high mixing entropy and sluggish cooperative diffusion enhance the formation of simple solid-solution phases and submicronic structures with nanoprecipitates in the alloys with multiprincipal elements rather than intermetallic compounds.