Rheology and ultrasonic properties of Pt57.5Ni5.3Cu14.7P22.5 liquid

Abstract

The equilibrium and nonequilibrium viscosity and isoconfigurational shear modulus of Pt 57.5 Ni 5.3 Cu 14.7 P 22.5 supercooled liquid are evaluated using continuous-strain-rate compression experiments and ultrasonic measurements. By means of a thermodynamically-consistent cooperative shear model, variations in viscosity with both temperature and strain rate are uniquely correlated to the variations in isoconfigurational shear modulus, which leads to an accurate prediction of the liquid fragility and to a good description of the liquid strain-rate sensitivity. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2732822͔The Pt-Ni-Cu-P bulk-glass forming system 1 is known to form one of the toughest bulk metallic glasses to date, 2-4 characterized by a fracture toughness value of ϳ80 MPa m 1/2 . The inherent toughness of this system is shown to be a consequence of its tendency to undergo extensive shear-band networking prior to fracture. 2 This tendency has been primarily attributed to its high Poisson's ratio ͑ϳ0.42͒, which designates that the material favors accommodation of stress by shear. Interestingly, Poisson's ratios of metallic glasses were recently shown to be directly correlated to the rheology of their undercooled liquid state, and specifically to the liquid fragility. 5 In a recent rheological study 6 it is demonstrated that Pt-based liquid is indeed one of the most fragile metallic glass-forming liquids, which to some extent explains its inherently tough nature. In the present study we employ continuous-strain-rate compression experiments and acoustic measurements in conjunction with a recently developed cooperative shear model 7-9 to assess the rheology and ultrasonic properties of Pt 57.5 Ni 5.3 Cu 14.7 P 22.5 liquid under equilibrium and nonequilibrium conditions.The rheology of the supercooled liquid was assessed using the continuous-strain-rate compression setup described in a previous study. 10 The alloy ingot was prepared by first prealloying Pt ͑99.9 mass %͒, Ni ͑99.9 mass %͒, and Cu ͑99.99 mass %͒ by induction melting, and then alloying P ͑99.999 mass %͒ by stepwise furnace heating. The specimens were prepared by first fluxing the alloy with B 2 O 3 , and subsequently casting it into 4 mm diameter rods, whose amorphous nature was verified by thermal analysis. The rods were cut and polished to produce 4 mm tall cylindrical specimens. The typical 2:1 geometric ratio was not adopted here, as the 1:1 ratio was found more appropriate for geometrically constraining the specimens against unusually excessive barreling ͑possibly related to a high Poisson's ratio͒. The compression experiments were performed for an adequate duration to ensure that a steady-state flow stress had been attained. The strain-rate dependent viscosity measured in the temperature range of 473 to 523 K is presented in Fig. 1. The strain-rate dependence exhibits the typical trend observed in other glass forming systems: in the low strain rate limit, viscosity is stabilized at the Newtonian limit characterized by a strainrate se...

Anelastic to Plastic Transition in Metallic Glass-Forming Liquids

“…This suggests that the mean curvature of the potential energy density function averaged over all instantaneously occupied basins in steady flow has the same dependence on potential energy as the curvature within a single megabasin in transient deformation. This result provides support for rheological laws based on averages over instantaneously occupied megabasins during steady flow [9][10][11].…”

“…The existence of a steady-state high-frequency shear modulus suggests that G is a thermodynamic property of the material associated with the configurational energy state defined by temperature and strain rate. Indeed, G has previously been shown to be uniquely and reversibly dependent on temperature [10,11,13] as well as strain rate [9,11]. More precisely, G was found to be a unique decreasing function of h independent of whether h is induced by thermal excitation or mechanical deformation [11,15].…”

“…Johnson and Samwer [8] have recently shown that, by employing a sinusoidal function to describe the megabasin potential energy density, a scaling law for the yield strength of a frozen-in configuration arises in terms of the curvature of the potential energy density function (i.e., the isoconfigurational shear modulus), revealing a universal shear strain limit of c 0:036. More recently, Demetriou et al [9][10][11] extended this sinusoidal potential to describe the average interbasin configurational hopping arriving at accurate Newtonian and nonNewtonian viscosity laws. In the present study, we seek to explore the relevance of the underlying configurational hopping mechanisms to Argon's concept of ''dressed'' STZ's.…”

“…For the experiments, we utilized amorphous Pd 43 Ni 10 Cu 27 P 20 specimens that were annealed and structurally relaxed to a reference state at 548 K (21 K below the calorimetric glass transition temperature T g ) for 48 hours prior to testing. Constant strain-rate compression experiments at 548 K and 1 10 ÿ4 s ÿ1 strain rate were performed using the setup described in Ref.…”

Fragility of iron-based glasses

“…The fragility of this Fe-based glassformer is unusually high, surpassing even that of the Ptbased glass former, which was thought to be the most fragile among the bulk metallic glass-formers. 18 TABLE Interestingly, the large fragility range of Fe-based glassformers appears to roughly reflect the broadly-varying GFA of these systems. Specifically, the Fe-based glasses whose fragilities, m, are estimated here to range from 43 to 65 have critical rod diameters for glass formation, d c , ranging from 3 to 16 mm.…”