Effects of Electron Beam Welding on Microstructure, Microhardness, and Electrical Conductivity of Cu-Cr-Zr Alloy Plates P.K.C. Kanigalpula, Arya Chatterjee, D.K. Pratihar, M.N. Jha, and J. Derose (Submitted March 30, 2015; in revised form September 11, 2015; published online November 4, 2015) In this study, the effects of electron beam welding on the microstructure, microhardness, and electrical conductivity of precipitation-hardened Cu-0.804%Cr-0.063%Zr (wt.%) alloy plates were investigated. Experiments were carried out following a central composite design of experiments. Five welding schedules yielding the higher hardness were chosen and then were subjected to standard metallographic and various microscopy techniques to reveal the type, morphology, and distribution of the precipitates and to obtain the sub-structural information from the weld zone. X-ray diffraction studies revealed predominant formation of intermetallic phases in the welded zones of some of the samples, which could have resulted in higher hardness and better electrical conductivity compared to those of other ones. Microhardness values in the fusion zone and heat-affected zone were found to be less than that of the parent material. The mechanism of damage in Cu-Cr-Zr plates due to welding was also explained. Keywords Cu-Cr-Zr alloy, electrical conductivity, electron beam welding, microhardness, precipitate volume fraction, x-ray diffraction 1. Introduction Precipitation-hardened (PH) Cu-Cr-Zr alloys are used as structural material for actively cooled high heat flux plasma facing components (PFC), such as toroidal pump limiter (TPL) and guard limiters, (Ref 1-4), and are potential candidates for applications in fusion devices of the International Thermonu- clear Experimental Reactor (ITER) because of their excellent electrical and thermal conductivities, corrosion resistance, high strength, fatigue resistance, and ease of manufacture (Ref 5). The focus on this alloy is mainly toward checking the possibilities of strengthening pure copper with fine dispersion of second phases in Cu-Cr-Zr alloys, as the improved strength with high thermal or electrical conductivity is essential for heat sink materials. The high thermal or electrical conductivity of these alloys could be due to low solubility of chromium (0.6- 0.9%) and zirconium (0.03-0.25%) in the Cu matrix, whereas the improved strength was achieved through precipitation strengthening mechanisms (Ref 3, 4, 6). Reports related to microstructural features, namely grain size and precipitates of Cu-Cr-Zr alloys with variations in Cr and Zr contents in the ranges of 0.31-1.2 and 0.1-0.21 wt.%, respectively, are available in the literature (Ref 7-9). These reports mainly evaluated the effects of Cr and Zr on precipitation behavior of the alloy on their mechanical properties. Usually, these alloys are subjected to various combinations of processing stages, namely annealing, solu- tionizing, aging, cold deformation, equal channel angular pressing, and continuous extrusion to get improved mechan- ical and electrical properties (Ref 7, 8, 10). To reach the optimized combination of physical properties with improved mechanical properties, such as hardness, strength, and ductil- ity, different types of aging treatments were studied for these alloys (Ref 11-13). Studies of the thermal fatigue behavior of Cu-Cr-Zr alloys were also reported by previous investigators (Ref 14). PH Cu-Cr-Zr alloys are heat-treatable alloys, which exhibit high strength in the peak-aged condition, and good fracture toughness and fatigue properties in both irradiated and non- irradiated conditions. However, the softening temperature of heat-treated PH Cu-Cr-Zr alloy is 500 °C, which makes it very suitable for fabrication of components subjected to high heat flux (Ref 15). During welding, the precipitates get completely dissolved in the melted zone of the weld joint and results in lower strength and softening temperature. Hence, it is important to maintain the structural reliability of the components made of Cu-Cr-Zr alloys and also, necessary to understand the effects of electron beam welding (EBW) on mechanical and physical properties, such as microhardness and electrical conductivity of this alloy. A very few reports are available on the welding of Cu-Cr-Zr alloy. Schlosser et al. (Ref 16) had analyzed the three- generation technologies for the actively cooled PFC used in Tore-Supra (TS) since 1985. Their work focused primarily on the bonding between a carbon fiber composite (CFC) made through active metal casting (AMC) process and heat sink made from Cu-Cr-Zr alloy. The effects of alloying elements, P.K.C. Kanigalpula and D.K. Pratihar, Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India; Arya Chatterjee, Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India; and M.N. Jha and J. Derose, Power Beam Equipment Design Section, Bhaba Atomic Research Centre, Trombay, Mumbai 400085, India. Contact e-mails: kpkchakravarthy@gmail.com, arya@metal. iitkgp.ernet.in, dkpra@mech.iitkgp.ernet.in, mnjha08@gmail.com, and derose@barc.gov.in. JMEPEG (2015) 24:4681–4690 ÓASM International DOI: 10.1007/s11665-015-1790-9 1059-9495/$19.00 Journal of Materials Engineering and Performance Volume 24(12) December 2015—4681