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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]