Performance of Cu–TiC alloy electrodes developed by reaction milling for electrical-resistance welding Rodrigo H. Palma ∗ , Aquiles H. Sep ´ ulveda, Rodrigo A. Espinoza, Roberto C. Montiglio Department of Mechanical Engineering, Universidad de Chile, Beauchef 850, Casilla 2777, Piso 4, Torre Central, Santiago 6511265, Chile Abstract The performance of a nominal-composition Cu–5vol.% TiC alloy, prepared via powder metallurgy, was evaluated when such material was used as electrodes for electrical-resistance welding. Starting from Cu, Ti and graphite powders, flakes of the alloy were synthesized by reaction milling in a high-energy mill; alloy bars 6 mm diameter were then produced by hot extruding such flakes. Electrodes performance was evaluated by means of the following indexes: tip shortening, tip widening, and mass loss. Electrolytic copper electrodes were used as reference. The results obtained clearly demonstrate that the Cu–TiC electrodes prepared from powders synthesized by reaction milling have a remarkably better performance than those manufactured from electrolytic copper. Keywords: Welding; Electrodes; Mechanical alloying; Reaction milling; Copper alloys; Dispersion-strengthening 1. Introduction The electrical-resistance welding process reached full de- velopment in the production of aviation assemblies, car chas- sis and bodies, metallic furniture, and other applications, after World War II. This welding process uses Cu and Cu alloys as the electrode material. Electrical-resistance welding involves passing a high current at a low voltage through a circuit closed by the pieces to be welded; these pieces are maintained in close contact with the two electrodes by means of an applied pressure, see Fig. 1. The heat generated by the Joule effect is enough to produce local fusion of the pieces under pressure, leading to an autogenously forged union. Thus, electrode ma- terials must exhibit high electrical and thermal conductivities, combined with high strength, at elevated temperatures. The elevated-temperature strength of metal alloys can gen- erally be improved by the inclusion of a low volume fraction (0.02–0.05) of finely dispersed ceramic particles [1]. Insol- ∗ Corresponding author. Tel.: +56 2 6784591; fax: +56 2 6988453. E-mail address: rhpalma@ing.uchile.cl (R.H. Palma). uble particles are required to allow thermal and electrical conductivities to remain within acceptable practical limits. These dispersoids must be thermodynamically stable, homo- geneously distributed in the metal matrix and of nanometric size. The elevated-temperature strength of a metallic matrix reinforced with nano-dispersoids is controlled by two princi- pal mechanisms: interactions between dispersoids and grain boundaries [2] and interactions between dislocations and ma- trix/dispersoid interphases [3]. Reaction milling is an effective approach to introduce nanometric dispersoids in a Cu matrix [4,5]. Mechanical alloying and its particular form of reaction milling have been recently reviewed by Lu and Lai [1]. Mechanical alloying is a ball mill process invented around 1966, where a powder mix- ture is subjected to high-energy collisions from the balls. The two most important events involved in mechanical alloying are the repeated welding and fracturing of the powder mix- ture, permitting the solid-state synthesis of materials which are usually not possible to obtain by traditional techniques. Alloys with different combinations of metals, even using a starting mixture of low- and high-melting temperature