Kinetics of Structural Relaxation in Metal Glasses
- PDF / 268,453 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 81 Downloads / 219 Views
glasses. EXPERIMENTAL PROCEDURE The amorphous NiS0P 2 0 , Fe8 2 B1 8, Fe 4 0 Ni 4 0 B20 , Ti-Cu- and Ti-Ni-based amorphous alloys were prepared with the melt spinning technique. Amorphous structure was verified by X-ray diffraction. Thermopower ET as a function of an annealing time ta at different annealing temperatures Ta < Tx (where Tx is a crystallization temperature) was measured in a couple containing annealed and asquenched alloys of a same composition. Thus, we obtained a relative thermopower data. All specimens were in Ti container during annealing. Temperatures of the "hot' and "cool" ends of couple were 68 and 15 0 C, respectively. RESULTS AND DISCUSSION In the present paper we attempt to analyze the peculiarities of the structural relaxation process in the different type metal glasses using the evolution of thermopower data at the structural relaxation process. Changing of thermopower ET is small (some [tV/K) and increases with isothermal annealing time ta and annealing temperature Ta increasing. The most typical dependencies of ET(t) with the Ta = Const are shown on figs. 1, 2. 357 Mat. Res. Soc. Symp. Proc. Vol. 398 01996 Materials Research Society
0
050
10
150
200
250
300
U
-5
TT=470 K -15
~oT-=640
20
-25
l
i-T =520 K wT=570 K xT=620 K K
i
t, min
Fig. 1. Thermopower vs. annealing time curves for Fe 8 2B18 amorphous alloys.
Fig. 2. Thermopower vs. annealing Ti 46 Cu 45Ni 5 Si 2P 2 (0) amorphous alloys.
time
curves
for
Ti 4gCu 45 Ni 5 P 2
(*),
The behaviour of ET(t) curves certificates that relaxation process is multistage. It is seen that thermopower tend to saturation with annealing time increasing. To treat the experimental results we used the theory described in [3] for the crystalline state. Koehler, Seitz and Bauerle have made the first attempt to exploring the vacancy lives in Au. They have defined that effective diffusion constant Deff and effective migration 358
energy Em can be expressed in terms of Em1 and Em 2 (the energy of migration of a single and divacancy, respectively). This migration energy Em depends on annealing temperature and vacancy concentration. The general expression of the differential equations describing the kinetics of single, di-, three- and tetravacanciesis presented in [3]. Meanwhile taking into account the Egami view [4] of structural defects in amorphous materials we attempted to apply the above mentioned theory to amorphous systems. In our investigations we use the equations describing diffusion of single and divacancies. And we considered two type atom complexes migration. Namely, transition metal (TM) atoms and transition metal - metaloid (TM-M) complexes instead of single and divacancies, respectively. So, dc, =_168v, ex dc1
E_-c2 EA
dc2 dc =168veex
4.•T
Iv
ex (E'±+B, 2- 20 V, x E1 1 ex kT ) ex(kT)1cc ex14 l{ EIm+B=j)
-14vex
-
-20v,1 ex
(Ex4 •jcc _-k-1T)C C2
(1)
(2)
where cl, c 2 are the concentrations of TM and TM-M complexes, respectively, v is a vibration frequency of a separate atom and a complex. Eml, Em2 are correspond
Data Loading...
