Influence of two-step ball-milling condition on electrical and mechanical properties of TiC-dispersion-strengthened Cu alloys Fenglin Wang a,b , Yunping Li b,⇑ , Kenta Yamanaka b , Kimio Wakon b , Koichi Harata b , Akihiko Chiba b a Department of Materials Processing, Tohoku University, Sendai 980-8579, Japan b Institute for Materials Research, Tohoku University, Sendai 980-0812, Japan article info Article history: Received 27 June 2014 Accepted 8 August 2014 Available online 19 August 2014 Keywords: Two-step ball-milling Dispersion-strengthened copper alloy In-situ reaction abstract TiC-dispersion-strengthened Cu alloys were prepared by a two-step ball-milling (BM) process followed by sparks plasma sintering (SPS), heat treatment and hot rolling in sequence. The two-step BM process is composed of a pre-ball-milling (pre-BM) on both Ti and graphite powders as well as a subsequent homogenizing by BM together with Cu powder. Microstructure evolution analysis was performed to evaluate the effects of BM conditions on the electrical and mechanical properties of Cu-based alloys. The X-ray results revealed that titanium carbide (TiC) formed from Ti and C under high impact energy BM. Moreover, the formation of TiC during the SPS and heat treatment processes was found to more ben- eficial in enhancing the mechanical properties of alloy. The residual Ti in Cu matrix was found to be the predominant factor lowering the electrical conductivity of Cu–Ti–C alloys. Crown Copyright Ó 2014 Published by Elsevier Ltd. All rights reserved. 1. Introduction Copper alloys with both high electrical conductivity and high strength are suitable candidates for the use in high performance electrical applications. To obtain high mechanical property of cop- per alloy via dispersion-strengthening has been proved to be a promising method. Carbides, oxides, borides and nitrides are fre- quently used as the second reinforcing phases that are homoge- nously dispersed in copper matrix [1–4], where titanium carbide (TiC) was usually selected to strengthen copper due to its desirable properties such as high melting point, great hardness and high chemical stability [5]. This dispersion-strengthening effect is strongly dependent on not only the interface properties between reinforcement and matrix, but also the size and distribution of reinforcement particles. The most common methods producing composites reinforced with the hard particles are casting and powder metallurgy (PM). PM route usually includes high-energy BM, compaction and sinter- ing or extrusion. The high-energy BM process has been widely uti- lized because its ability to incorporate nano-scaled reinforcement into metal matrix. The direct mixing of reinforcement and metallic matrix is generally referred as ex-situ technology. In contrast, in-situ technology involves the synthesis of reinforcement in metallic matrix by chemical reaction among the starting materials [6,7]. During the fabrication process of dispersion-strengthened Cu alloys, the agglomeration of reinforced particles generally leads to a deteriorated mechanical property. There have been some reports suggesting that the geometries, densities and the differences in reinforced particles could affect the particles agglomeration [8]. Although the high-energy BM is considered as a suitable method for improving the reinforced particles distribution, some disadvan- tages such as the influence of powders contamination by gaseous elements on densification during sintering process and the decreased powders compressibility by cold-worked structures will appear [9,10]. There have been many reports on the Cu–Ti–C alloys. Some of them focus on the reaction behavior of self-propagating during high-temperature synthesis of TiC [11–13]. The synthesis of nano-sized TiC powder by mechanical milling of titanium and graphite powders was also reported [14]. There are also some pre- vious works on fabrication of Cu–TiC composite by high-energy BM [15,16]. The creep behavior, strain and fracture mechanism have been investigated with the prepared Cu–TiC composites. Besides, the remarkably higher electrodes performance of dispersion- strengthened Cu–TiC alloy than that of electrolytic Cu electrodes has been demonstrated due to the homogeneous distribution of nanometric TiC dispersoids in the Cu alloy matrix [17]. BM process is a critical step throughout the preparation process of dispersion- strengthened materials. BM conditions have a significant effect on the properties of dispersion-strengthened materials, involving the http://dx.doi.org/10.1016/j.matdes.2014.08.027 0261-3069/Crown Copyright Ó 2014 Published by Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +81 22 215 2452. E-mail address: lyping@imr.tohoku.ac.jp (Y. Li). Materials and Design 64 (2014) 441–449 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes