A new surface-alloying technique for pure copper
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A new surface-alloying technique for pure copper M-X. Zhang, K. Reilly, and P.M. Kelly Department of Mining, Minerals and Materials Engineering, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia (Received 15 March 1999; accepted 8 May 1999)
A totally new technique of surface modification—thermal surface-alloying treatment for pure copper—was developed. A 0.2–1.8 mm copper alloy layer, which has a hardness 4 to 5 times higher than the pure copper substrate, was formed after the treatment. The significance of this technique is that the surface of pure copper can be efficiently hardened without significant reduction of the overall thermal and electrical conductivity. Variations of composition and microstructure in the alloy layer were studied after pure copper was surface alloy treated with aluminum.
I. INTRODUCTION
Pure copper has the highest thermal and electrical conductivity of any common metal. It therefore finds wide application as an electrical conductor (electric wires and cables) and as a thermal conductor (cooling coils, saucepans, etc.). Unfortunately, pure copper is extremely soft, has low strength, and, therefore, poor wear resistance. Pure copper components can only be used in low-stress situations and are susceptible to wear. The most obvious approach to improving the mechanical properties and wear resistance of copper is to alloy the material, and much effort has been devoted to the development of stronger copper alloys. The problem with this approach is that every feasible alloying element dramatically reduces the conductivity of copper, and the main benefits of the metal are seriously degraded. Another possible approach to increase the hardness and wear resistance of pure copper is surface treatment. The available surface modification techniques and processes1 can be divided into three groups: coating, surface hardening, and surface alloying. A poorly bonded coating may peel off or be damaged in service. Thus some very expensive equipment is needed to increase the adherence of the coating to the substrate, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD).1 Surface hardening is only used in some ferrous alloys, such as surface quenching treatment of steels. Surface alloying leads to the formation of a hard alloy layer on the surface of the substrate and a consequential improvement in the properties of the components. Because this surface layer is an integral part of the substrate, no “coating adherence” problem exists. In the past two decades, high-energy surface modification techniques have been developed. These include plasma arc alloying, laser alloying, electron beam alloying, ion beam alloying, electrical discharge alloying, and their combinations.2–7 J. Mater. Res., Vol. 14, No. 8, Aug 1999
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All these surface alloying processes involve melting the surface layer and adding alloying elements. Not only are very expensive high-energy generators often req
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