The Effect of Mill Temper on the Mechanical and Magnetoresistive Properties of Oxygen-Free Copper in Liquid Helium

Abstract

Accurate knowledge of the resistive, magnetoresistive, and mechanical properties of the oxygen-free copper used to stabilize practical superconductors is a necessity for optimum and dependable design of magnet systems. These properties are strongly influenced by: the source of the ore; the specific way in which the ore is processed; the definition used for soft temper by the producer, including the mill anneal method; subsequent mechanical processing by the producer and/or the wire manufacturer; and thermal treatments, both desired and inadvertent, that may occur anywhere along the way. In the program reported on here, we acquired samples of oxygen-free copper in various states of anneal and temper from a large number of suppliers. We then measured the transverse magnetoresistance and the mechanical properties (stress-strain) of these samples at 4 K. Selected samples were further cold worked and/or reannealed and then remeasured. In addition, special tests were performed on particular samples. The range of tests is shown by the block diagram of Fig. 1. Space allows presentation of only a few of the results here. Others have been published elsewhere,¹ and a final report covering all of the work to date is now in press.²

Research sponsored by the International Copper Research Association (INCRA).