Laser and particle beam irradiation effects in amorphous metals
- PDF / 1,103,127 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 63 Downloads / 212 Views
NN10.1.1
Laser and particle beam irradiation effects in amorphous metals Monica Sorescu Physics Department, Duquesne University, Pittsburgh, PA 15282-0321, U.S.A. ABSTRACT In view of the potential use of amorphous magnets as radiation-resistant materials, we performed a comparative study between laser and particle beam induced effects in amorphous alloy systems. We irradiated Fe81B13.5 Si3.5C2, Fe40Ni38Mo4B18, Fe66Co18B15Si1 and Fe72.6Cr22Al4.8Si0.3Y0.3 with pulsed laser radiation as well as with high (W=7 MeV) and low energy (W=30 and 50 keV) electrons and with 2.8 MeV alpha particles. The irradiation effects in these systems were investigated using several complementary techniques: transmission and conversion electron Mössbauer spectroscopy, magnetometry and electron microscopy. We were able to deduce details of the mechanism of magnetic texture formation and of the amorphous-to-crystalline phase transformations in the studied amorphous alloys. INTRODUCTION The fact that the coexistence of magnetism with a noncrystalline lattice is not yet understood made amorphous metals the subject of intense research efforts. The amorphous state is metastable and irradiation of the amorphous structure with different types of radiation induces unconventional pathways for the crystallization or nanocrystallization of these systems. From this point of view it is expected that the amorphous alloys behave differently under laser irradiation than under particle beam irradiation. By performing a comparative study of the two classes of irradiation effects, we were able to contrast and compare the devitrification processes in the systems under investigation. In particular, the laser irradiation of amorphous metals was performed in connection with Mössbauer spectroscopy studies, such that this method combines an extremely sharp tool for exciting the amorphous structure (quenching rates of 1014 K/s) with a spectroscopic technique that has the highest resolution known in physics [1-16]. EXPERIMENTAL DETAILS
Amorphous alloys Fe81B13.5 Si3.5C2 (λs=27 ppm), Fe40Ni38Mo4B18 (λs=12 ppm), Fe66Co18B15Si1 (λs=35 ppm) and Fe72.6Cr22Al4.8Si0.3Y0.3 (λs=0 ppm) were supplied by Allied Signal Inc. in the form of 20 µm thick ribbons. Square samples (2x2 cm) were cut from the foils and exposed on the shiny side to the 248 nm radiation generated by a KrF excimer laser with the pulse width of 8 ns, capable of giving a maximum energy of 450 mJ/pulse. A single pulse energy density of 3 J/cm2 was achieved by focusing with a cylindrical fused silica lens to a spot-size of 0.5x5 mm2 with 0.5 mm overlaps. In a first set of experiments, amorphous samples of Fe81B13.5 Si3.5C2 were irradiated with 2, 5 and 10 laser pulses per spot at a repetition rate of 5 Hz. An acceptable degree of homogeneity
NN10.1.2
was obtained by laser beam scanning of the sample surface, which was placed on a x-y-z micrometer translation stage. In another set of experiments, samples of Fe81B13.5 Si3.5C2 ribbon were exposed to a Nd:YAG laser (λ=532 nm, τ=8 ns, Φ=30 J/cm2, ν=10 Hz). In add
Data Loading...
