Characteristics of the Structural and Johari–Goldstein Relaxations in Pd-Based Metallic Glass-Forming Liquids

Abstract

The dynamics of Pd-based metallic glass-forming liquids (Pd(40)Ni(10)Cu(30)P(20), Pd(42.5)Ni(7.5)Cu(30)P(20), Pd(40)Ni(40)P(20), and Pd(30)Ni(50)P(20)) was studied by mechanical spectroscopy and modulated differential scanning calorimetry (MDSC). We found that the change in composition has a significant effect on the α relaxation dynamics; the largest difference corresponds to an increase of the glass transition temperature Tg of ∼ 15 K, for materials in which 30% Ni was substituted by 30% Cu (i.e., from Pd(40)Ni(40)P(20) to Pd(40)Ni(10)Cu(30)P(20)). We also found that all Pd-based metallic glasses have very similar fragilities, 59 < m < 67, and Kohlrausch stretched exponents, 0.59 < βKWW < 0.60. It is interesting that the values of m and βKWW correlate well with the general relation proposed by Böhmer et al. for nonmetallic glass formers (Böhmer, R.; et al. J. Chem. Phys. 1993, 99, 4201-4209), which for the observed βKWW values predicts 58 < m < 61. From a linear deconvolution of the α and β relaxations, we find that the substitution of the Ni with Cu induced a large change in the time constant of the Johari-Goldstein relaxation, τβ. The activation energy, Uβ, of the β relaxation was largely independent of chemical composition. In all cases, 25 < Uβ/RT < 28, a range in agreement with results for other glass formers (Kudlik, A.; et al. Europhys. Lett. 1997, 40, 649-654 and Ngai, K. L.; et al. Phys. Rev. E 2004, 69, 031501). From the heat capacity and mechanical loss, estimates were obtained for the number of dynamically correlated units, Nc; we find significantly larger values for these metallic glass-forming liquids than Nc for other glass-forming materials.

Characteristics of stress relaxation kinetics of La 60 Ni 15 Al 25 bulk metallic glass

“…On the other hand, the peak position of the a relaxation is independent of the physical aging when annealing is below T g . The experimental phenomenon is consistent with the previous results [39,40]. As proposed in the previous investigations, the b relaxation of the metallic glasses is ascribed to the structural heterogeneity or local motion of the ''defects'' [41].…”

Modeling of the Sub-Tg Relaxation Spectrum of Pd42.5Ni7.5Cu30P20 Metallic Glass

“…This shoulder is associated with a secondary process (β-relaxation) and, although with different degrees of intensity, was observed in all Pd-based alloys 3 . The presence of secondary relaxations has been found in many other metallic glasses 11,12 .…”

Amorphous physics and materials: Secondary relaxation and dynamic heterogeneity in metallic glasses: A brief review

“…[45] A similar behaviour was verified for the Pd-based and La-based metallic glass systems in which relaxation tends to be suppressed with the increasing concentration of Ni, the element causing a large mixing enthalpy mismatch. [44,46,47] Structural relaxation like physical aging and rejuvenation is an intrinsic feature of glassy materials, which originates from local processes that causes the whole system migrating into a more energetically stable state [49][50][51] . In practice, glasses with enhanced thermodynamic and kinetic stability are attractive for both scientific research and engineering applications.…”