Sm-Co permanent magnets: effects of fast neutron irradiation
- PDF / 498,200 Bytes
- 5 Pages / 594 x 774 pts Page_size
- 27 Downloads / 205 Views
I.
II.
INTRODUCTION
RADIATION-induced changes in magnetic properties have been studied in rare-earth permanent magnets, most recently in Nd-Fe-B tl-41 and earlier in the Sm-Co ts-81 alloys. In general, these studies find the Sm-Co magnets to have better radiation resistance, but many details of their response to radiation are not clear. For instance, prior studies on Sm-Co magnets only report on their behavior when irradiated at temperatures above ambient and in the absence of an opposed (bucking) magnetic field. However, certain applications in a radiation environment for beam-steering magnets in accelerators require their use at subambient temperatures and in the superimposed magnetic field of adjacent magnets. Since Sm-Co magnets are strong candidates for use in these applications, it is important to characterize how their response to radiation varies with temperature and applied field. Both of these variables can be expected to affect rates of radiation damage. An earlier study of radiation-induced remanence decay for Nd-Fe-B magnets t21 showed that the decay rate increased with temperature of irradiation above room temperature. Also, the decay rate was found to increase monotonically with the demagnetizing field of the sample, t31 The latter is determined by the combined effects due to the length-to-diameter (L/D) ratio of the sample and an externally applied bucking field, both of which are design considerations for magnets in accelerator quadrupoles. In this paper, our objective is to compare radiationinduced decay with neutron fluence in different commercially available Sm-Co magnet materials as affected by (1) subambient temperatures and (2) an externally applied bucking field. We do this in the temperature range from 75 to 28 1 K with and without a bucking field of 5.5 kOe.
J.R. COST and R.D. BROWN, Staff Members, are with the Los Alamos National Laboratory, Los Alamos, NM 87545. This paper is based on a presentation made in the symposium "Irradiation-Enhanced Materials Science and Engineering" presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, Illinois, September 25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD. . METALLURGICALTRANSACTIONS A
EXPERIMENTAL
A. Samples Three each of SmCo5 and Sm2COl7 magnet materials were studied. These materials were obtained in bulk form from the manufacturers listed in Table I. Also shown in this table are the manufacturers' specifications for the residual induction and the intrinsic coercivity. Samples were prepared for irradiation by demagnetizing if necessary, cutting from the bulk material with a liquid-cooled diamond saw, and then lightly grinding to round the corners. The final shape was a fight-circular cylinder nominally 0.75-mm thick and 6.3 mm in diameter with the preferred direction of magnetization along the cylindrical axis. Following cutting, the samples were polished on 400-grit paper and magnetized to saturation in a pulse charger in a field
Data Loading...
