SFT Stacking fault tetrahedral TCH Tension and compression hold

4.20.1 Introduction

Copper alloys are prime candidates for high heat flux applications in fusion energy systems. High heat flux is a major challenge for various fusion devices because of the extremely high energy density required in controlled thermonuclear fusion. The removal of a large amount of heat generated in the plasma through the first wall structure imposes a major constraint on the component design life. Materials with high con­ductivity are needed to assist heat transfer to the coolant and to reduce the thermal stress for pulsed mode of operation.

A number of issues must be considered in the selection of materials for high heat flux applications in fusion reactors. While high conductivity is the key property for such applications, high strength and radiation resistance are also essential for the effective performance of materials in a high heat flux, high irradiation environment. In addition, fatigue behavior is a major concern for many high heat flux applica­tions because of planned or inadvertent changes in the thermal loading. Pure copper has high thermal con­ductivity but rather low strength, and therefore its application as heat sinks is limited. The strength of copper can be improved by various strengthening mechanisms. Among them, precipitation hardening and dispersion strengthening are the two most viable mechanisms for improving the strength of copper while retaining its high electrical and thermal con­ductivities. A number ofprecipitation-hardened (PH) and dispersion-strengthened (DS) copper alloys are commercially available, and have been evaluated for fusion applications, for example, PH CuCrZr, CuNiBe, CuNiSi, and DS GlidCop® Al15, Al25, Al60, MAGT-0.2, etc. Two copper alloys that are most appealing are PH CuCrZr and DS CuAl25. Surveys of copper alloys for fusion applications were conducted by Butterworth and Forty1 and Zinkle and Fabritsiev.2

In this chapter, a brief description of pure copper and several copper alloys of interest to fusion appli­cations is presented, followed by a summary of their physical and mechanical properties. The radiation effects on the physical and mechanical properties of copper and copper alloys as well as their irradiated microstructure are then discussed. Joining techniques for plasma facing components in fusion reactors are also discussed.