Irradiation induced precipitation in tungsten based, W-Re alloys
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I.
INTRODUCTION
HIGH-temperature irradiation of binary alloys has received a great deal of attention in recent years. Although many aspects of the behavior of alloys, such as point defect clustering to form dislocation loops and cavities during high temperature irradiation, are similar to those occurring in pure metals, the situation as a whole is invariably more complex. Considerable insight has been gained into the highly interrelated phenomena of solute-defect trapping, solute segregation, phase stability, and void swelling. An important motivation for much of the work has been the need to understand the behavior of austenitic stainless steels for application in fuel cladding and core structural components of fast breeder reactors and for the first wall materials of proposed fusion reactors. In these steels the role of the second phase particles and redistribution of solutes is often dominant in determining the mechanical properties and void swelling characteristics of the material. The topics of solute segregation and phase stability during irradiation were the subject of two recent meetings, the proceedings of which 1'2 contain a wealth of information plus reviews on radiation induced segregation 3 and phase stability under irradiation. 4'5 The purpose of this paper is to describe the behavior observed in three tungsten based, W-Re alloys which were irradiated at relatively high temperatures with fast neutrons. Both microscopy and bulk property measurements were employed, and correlation of the two types of results yielded insights which could not have been obtained from either type of experiment alone. The significance of this work is twofold. First, it provides a further example that neutron irradiation can produce unexpected precipitation phenomena in nominally solid solution alloys. Second, these alloys have been used for fuel element center-line temperature measurements, and the results indicate that in-reactor R. K. WILLIAMS, E W. WIFFEN, J. BENTLEY, andJ. O. STIEGLER are all Metallurgists with Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37830. Manuscript submitted April 6, 1982.
METALLURGICALTRANSACTIONS A
decalibration of these thermocouples is, in part, associated with the unexpected solid state precipitation phenomena. The paper is divided into sections describing the irradiation conditions and materials, experimental methods, experimental observations, and a discussion of the results. The three variables examined were neutron fluence, irradiation temperature, and Re content of the bcc alloy. The effects of irradiation temperature (900 to 1500 ~ and Re content (5, 11, and 25 pct Re) were studied at an approximately constant fast fluence ( - 6 • 1025n/m2). The effect of fluence was determined only for one composition (25 pct Re) and temperature (900 ~ The irradiation temperatures are uncertain, but the effect of Re content at constant temperature and fluence is the principal topic of this paper and this variation is well defined.
II.
IRRADIATION CONDITION
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