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High temperature deformation was probed in a La-based high entropy metallic glass with an evident slow β relaxation. The correlation between high configurational entropy and high temperature deformation mechanism was analyzed. On the one hand, by increasing the strain rate, the degree of deviation from Newtonian behavior in high entropy metallic glasses is lower than that of conventional metallic glasses, which is ascribed to the high configurational entropy. On the other hand, high configurational entropy leads to a decrease in activation volume in high temperature deformation of metallic glasses. Identifying the influence of high configurational entropy on the deformation mechanism paves the way for further understanding of the mechanical behavior of metallic glasses. [ABSTRACT FROM AUTHOR]

The transition behavior from a Ti-Cu alloy to nanoporous α-Ti, the kinetics of the dealloying reaction, and the coarsening of nanoporous α-Ti were studied, and the mechanism of dealloying with a metallic melt was investigated. When a Ti50Cu50 alloy disk was immersed in a Mg melt, the Cu content decreased from the surface of the disk, and transition layers of α-Ti and Ti2Cu were formed. The growth of the transition layers followed a parabolic law and the activation energy was close to those reported for the diffusion of solute atoms in liquids, suggesting that diffusion of Cu in the Mg melt mainly contributed to the rate-controlling process for the dealloying reaction. The temperature and time dependences of the ligament size followed a power law with an exponent of 4, suggesting that surface diffusion plays an important role in coarsening. All of these results are consistent with those reported for dealloying in aqueous solution, indicating that the underlying dealloying mechanism in a metallic melt is similar to that in aqueous solution. [ABSTRACT FROM AUTHOR]

A different dependence of apparent glass-forming ability (GFA) on casting-atmosphere pressure is observed in a Zr65Al7.5Ni10Cu17.5-xPdx (x=0–17.5) alloy system. Low-Pd alloys (x<12.5) reveal low GFA dependence, while high-Pd ones (x>=12.5) show high GFA dependence on atmosphere pressure applied during casting. The phenomenon is suggested to originate from the fact that for the high-Pd alloys, the transformation region of supercooled-liquid to quasicrystalline phase is located at the low-temperature side of the undercooled-liquid region where the atmosphere-pressure dependence of cooling characteristic coincidently takes place. The on-cooling phase transformation in the alloy system and the cooling mechanism during mold-casting process are discussed comprehensively. [ABSTRACT FROM AUTHOR]

The correlation of quasistatic and dynamic relaxations was discussed in a typical strong Zr55Al10Ni5Cu30 metallic glass from room temperature to Tg. The quasistatic relaxation behavior, investigated by high temperature compressive testing at a constant strain rate, was compared with dynamic tensile relaxation behavior. A correlation equation of the dynamic frequency and quasistatic strain rate was successfully deduced, and then its validity was experimentally confirmed in a fragile metallic glass. Using this correlation, the Cox–Merz rule, derived for correlating the steady-state and dynamic viscosities of the polymers, is found to be applicable to metallic glasses. [ABSTRACT FROM AUTHOR]

A single Zr65Al7.5Ni10Pd17.5 bulk metallic glass exhibits a large plastic strain of 6.6% during the compressive deformation process, which is attributed to the deformation mode with nanoscale multistep shear bands. We have observed that nanocrystals with a metastable fcc Zr2Ni structure containing several distorted icosahedral clusters are arranged in a “bandlike” formation in the glassy matrix around the multistep shear bands. This is recognized as direct evidence of the novel phenomenon of the restraint of shear band propagation owing to the dynamic precipitation of the nanocrystals. [ABSTRACT FROM AUTHOR]

The influences of sample diameter (D), Pd content (x), and hydrostatic pressure (P) in a chamber during casting on the structure of as cast Zr65Al7.5Ni10Cu17.5-xPdx(x=10, 17.5 at.%) bulk alloys were investigated. Zr65Al7.5Ni10Cu7.5Pd10 and Zr65Al7.5Ni10Pd17.5 alloys (D=3 mm) cast in a vacuum chamber (P∼4.0×10-3 Pa) were mainly of the tetragonal-Zr2Ni equilibrium phase and nanosize icosahedral primary phase, respectively, while the same alloys cast in inert argon gas at atmospheric pressure (P∼0.1 Mpa) were of the single glassy phase. Due to the higher cooling rate obtained by decreasing the sample diameter (D=2 mm) even in the vacuum chamber, the Zr65Al7.5Ni10Pd17.5 alloy was still of the icosahedral phase, while the Zr65Al7.5Ni10Cu7.5Pd10 alloy froze into a single glassy phase. These results indicate that the temperature- and timetransformation curves for the icosahedral and subsequent equilibrium phase formations in the alloy system shifts to a shorter time side with decreasing P, and the pressure sensitivity of the icosahedral phase formation increases with x. [ABSTRACT FROM AUTHOR]

The heat evolution of stress-induced structural disorder, ΔH[sub s]([variant_greek_epsilon]), of a Zr[sub 55]Al[sub 10]Ni[sub 5]Cu[sub 30] bulk metallic glass (BMG) during compressive constant ram-velocity deformation at the glass transition region (T[sub g]=680 K) was deduced from in situ measurements of temperature change of the deforming sample. At the transition from the linear to nonlinear viscoelasticity, the behavior of viscosity change with strain, η([variant_greek_epsilon]), is qualitatively consistent with the enthalpy evolution of the structural disordering, ΔH[sub s]([variant_greek_epsilon]), but not with the temperature change, ΔT([variant_greek_epsilon]). It is concluded that the initial softening deformation is due to the stress-induced structural disordering. The change in the nonlinearity, -log η ≡-log η /η[sub N], is found to be proportional to the ΔH[sub s] and the slope of ΔH[sub s](-log η) can be estimated to 400 J/mol, where η[sub N] is the Newtonian viscosity. On the other hand, the temperature raise, ΔT([variant_greek_epsilon]), is pronouncedly delayed as compared with the η ([variant_greek_epsilon]) and ΔH[sub s]([variant_greek_epsilon]) at the transition, but is determined by a product of stress and plastic strain-rate, σ·[variant_greek_epsilon][sub p], and is nearly proportional to it at the steady state. The slope of ΔT(σ·[variant_greek_epsilon][sub p]) can be estimated to 5.2×10[sup -2] K mol/W. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports the production of full strength compacts of metallic glass by warm extrusion of powders. Alloy used in the production of compacts; Temperature for maintaining the ductility of melt-spun alloy; Conduction of powder production and its consolidation in a closed powder metallurgy processing system.

In the present letter we compare the thermal conductivities of Cu- and Ni-based alloys in relation with their cooling rates and glass-forming abilities. The cooling rates obtained for Cu- and Ni-based bulk glass-forming alloys are found to scale with the thermal conductivities of the base elements. Relatively low thermal conductivity of Ni-based alloy compared to the Cu-based one explains its lower glass-forming ability. The results also indicate that the thermal conductivity of the molten alloy should be also used as an indicator of the glass-forming ability among the other factors. [ABSTRACT FROM AUTHOR]

Low ductility of glassy alloys prevents their technical application as structural materials. In this work, we study the Cu-based crystal-glassy composite material with good mechanical properties. Formation of the Cu[sub 10]Zr[sub 7] phase in the glassy matrix of a high-strength Cu[sub 50]Zr[sub 30]Ti[sub 10]Nb[sub 10] bulk alloy upon solidification led to higher Young’s modulus and enhanced ductility of such a composite compared to Cu-based glassy alloys. The as-cast structure was studied by x-ray diffraction and scanning electron microscopy. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The viscosity and flow stress of a bulk Pd[sub 40]Ni[sub 10]Cu[sub 30]P[sub 20] alloy glass near the glass transition were measured as a function of temperature and strain rate under compression. The steady-state viscosity of the glass for a given temperature remains constant at low strain rate, then decreases by many orders of magnitude above a critical strain rate. A master curve in term of the viscosity ratio η/η[sub N] and the product η[sub N]ε. has been constructed, where η and η[sub N] are, respectively, the steady-state viscosity and Newtonian viscosity, and ε. is the strain rate. The flow stress also can be represented in terms of the product η[sub N]ε.. The master curves are fitted with a simple stress relaxation of the form 1-exp[-t/λ] with t=ε.[sup -1]. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Edge-illumination x-ray phase contrast imaging (EI XPCI) is a non-interferometric phase-sensitive method where two absorption masks are employed. These masks are fabricated through a photolithography process followed by electroplating which is challenging in terms of yield as well as time- and cost-effectiveness. We report on the first implementation of EI XPCI with Pt-based metallic glass masks fabricated by an imprinting method. The new tested alloy exhibits good characteristics including high workability beside high x-ray attenuation. The fabrication process is easy and cheap, and can produce large-size masks for high x-ray energies within minutes. Imaging experiments show a good quality phase image, which confirms the potential of these masks to make the EI XPCI technique widely available and affordable.