JOURNAL OF MATERIALS SCIENCE 39 (2 0 0 4 ) 4659 – 4662 LETTERS Mechanochemical synthesis of nanocrystalline Al 2 O 3 dispersed copper SEUNG J. HWANG Department of Materials Science and Engineering, Daejin University, Pocheon, Kyung-gi, 487-711, South Korea D. WEXLER, A. CALKA School of Materials, Mechanical and Mechatronics Engineering, University of Wollongong, Northfields Ave., Wollongong NSW 2522, Australia Copper alloys dispersion, strengthened with aluminum oxide (Al 2 O 3 ), have great potential as a class of ox- ide dispersion strengthened (ODS) alloys with rela- tively high strengths, good phase stability and excel- lent conductivity at elevated temperatures. Applications of ODS Cu alloys include spot welding electrodes for the automotive assembly and electronic packaging in- dustries. ODS Cu alloys can be produced via several processing routes including internal oxidation [1–4], and casting and mechanical alloying [5, 6]. Unfor- tunately, internal oxidation tends to result in alloys with relatively low volume fractions of Al 2 O 3 dis- persoids, while casting and mechanical mixing both have the limitation that dispersoids produced are gen- erally too large to effectively limit dislocation motion [5]. Several reports have been published confirming that metals and alloys can be synthesized from their own ox- ides, using the technique of mechanochemical synthesis with an appropriate reductant [7, 8]. In particular, it has been demonstrated that high energy ball milling can induce the reduction reaction between CuO and Al, al- though, as yet, attempts to turn the powder product into useful ODS Cu alloys have met with problems due to the coarse nature of the final product [9, 10]. The partic- ular reduction reaction is highly exothermic and rapid Figure 1 XRD patterns obtained from the powders as a function of milling time. enough to be self-propagating, and the Al 2 O 3 disper- soid particles produced in the mill are subjected to such high temperatures that they over-coarsen. Ying et al. [11] attempted to overcome this problem by replacing Al with Cu-Al/Cu(Al) powder in order to slow down the reduction reaction. They synthesized a Cu-Al 2 O 3 nanocomposite precursor powder which, after consol- idation, produced Al 2 O 3 dispersoids less than 200 nm in size. Unfortunately, this was still not fine enough to give rise to significant dispersion strengthening [12]. In the current study it was intended to produce fine Al 2 O 3 dispersoid particles in a Cu matrix through ap- propriate mechanochemistry, using two approaches to further decrease the reaction rates and lower the re- action temperatures and energy. First, CuO was to be replaced with Cu 2 O for reasons outlined below. Sec- ond, excess Cu powder would be added as a diluent and thermal conductor to help remove heat from the system during milling with the aim of a less violent reaction or, at least retardation, of the combustion syn- thesis reaction in the mill [10, 11]. The reported heats of reaction of Cu oxides and Al are as follows [13]: 3CuO + 2Al → 3Cu + Al 2 O 3 −4.14 kJ/g 0022–2461 C  2004 Kluwer Academic Publishers 4659