Osami Haruyama

Free volume kinetics during sub-Tg structural relaxation of a bulk Pd40Ni40P20 metallic glass

The structural relaxation of bulk Pd40Ni40P20 metallic glass was examined under glass transition region. Assuming the isoconfigurational structural change, the room temperature density was measured after relaxing the bulk sample at 549K for any given time. The density relaxation was manifested by the process with a spectrum of relaxation times. The data were well described by a stretched exponential function with an average relaxation time of 1389s and Kohlrausch exponent of 0.66. The relaxation of reduced free volume was impossible to reproduce by means of bimolecular model for flow defect concentration.

Structural relaxation process in a bulk Pd40Cu30Ni10P20 metallic glass with a high Kauzmann temperature

The structural relaxation in a Pd 40 Cu 30 Ni 10 P 20 metallic glass was investigated by an electrical resistivity experiment. A chemical short range ordering (CSRO) process was observed together with the ordinary topological short range ordering (TSRO) one. It was found that the TSRO process was influenced by the B 2 O 3 flux treatment that was used to improve the thermal stability. The kinetics of CSRO were examined by measuring the isothermal change in the room temperature resistivity, ρ 300 , after annealing for a given time. The data obtained were successfully fitted by the relaxation function and the CSRO process was a thermally activated process with an energy spectrum.

Density and enthalpy relaxation behavior in a bulk Pd40Ni40P20 metallic glass

The kinetics of structural relaxation in a Pd40Ni40P20 bulk metallic glass was investigated by the volume relaxation due to density experiments and the enthalpy relaxation due to specific heat experiments. A two-step relaxation process was found in the volume relaxation, while the enthalpy relaxation seemed to be one-step relaxation process with a spectrum of relaxation times. First-step volume relaxation only in as-quenched glass was the process with a spread of relaxation times at lower relaxing temperature, while a Debye-type relaxation behavior was observed at higher temperature near Tg and in pre-annealed glass. The comparison of the kinetics of volume and enthalpy relaxations at the same temperature showed a disagreement with the prediction of free volume theory.

Relaxation Kinetics of Bulk Metallic Glasses below Glass Transition Temperature

The free volume relaxation just under the glass transition region was investigated by the high-resolution density measurement using the bulk metallic glasses with the compositions of Pd40Ni40P20 and Zr55Cu30Ni5Al10. The relaxation process was well described by a stretched exponential function with Kohlrausch exponent values less than unity. The reduced free volumes in an as-quenched state were estimated as 0.0117 and 0.0353 for Pd40Ni40P20 glass and Zr55Cu30Ni5Al10 glass, respectively. The specific heat curves Cp(T) for Pd42.5Cu30Ni7.5P20 alloy were obtained for the supercooled liquid, the equilibrium liquid and the crystallized alloy. The isenthalpic Kauzmann temperature TKH and isentropic Kauzmann temperature TKS were estimated as 471 K and 522 K, respectively, from the specific heat data.

Inhomogeneous Amorphous Structure of Bulk Metallic Glasses Examined from Structural Relaxation Kinetics

The kinetics of structural relaxation in fragile glass former, Pd46Cu35.5P18.5 BMG, and strong glass former, Zr50Cu40Al10 BMG, was investigated by volume relaxation. The former exhibited a relaxation phenomenon that is well understood by the local topological instability model, while the latter showed monotonous relaxation behavior over a wide range down to Tg-60 K. The discrepancy may be closely related to the difference in the fragility of both glasses.

Comparison of Mechanical Properties between As-Quenched and Annealed Metallic Glass Pd44Cu31Ni8P17

In order to examine the correlation between a mechanical property and an excess free volume for metallic glass Pd44Cu31Ni8P17, longitudinal and transverse ultrasonic velocities were measured to estimate longitudinal and transverse elastic constants, c11 and c44. An as-quenched sample, an annealed one at a temperature just below a glass transition temperature Tg and a crystalline one were prepared. The as-quenched sample contains the excess free volume depending on the preparing process. The Young’s modulus E, the Poisson’s ratio, a bulk modulus and c12 are estimated using c11 and c44. The values of c11, c 44 , c12 and E of the as-quenched one are smaller than those of the annealed sample losing excess free volume by about 0.2 % and much smaller than those of the crystalline one. The Poisson’s ratio for the as-quenched sample and the annealed one are 0.389 and 0.387, respectively, which are much larger than that for the crystalline one with 0.349.