Microstructure and wear behaviour of aluminium alloys containing embedded nanoscaled lead dispersoids Victoria Bhattacharya * , K. Chattopadhyay Department of Metallurgy, Indian Institute of Science, Bangalore 560 012, India Received 6 August 2003; received in revised form 16 December 2003; accepted 15 January 2004 Abstract We report the early stage friction and wear characteristics of aluminium containing nanosized lead dispersions. The nano- composite was produced by rapid solidification. The experimental results indicate a significant decrease in friction and wear rate in comparison to its coarse grained counterparts. We show that the observed results suggest an adhesive type of wear mechanism. However, increase in hardness due to refinement of the aluminium grains cannot quantitatively rationalize the results. We explore and discuss the role of nanoscaled lead particles and the mass transport between the sample and counterface via mechanical alloying, in the formation of tribolayers affecting the tribological properties. The plane view and cross-sectional transmission electron mi- croscopy reveals significant elongation as well as coarsening of the lead particles during the process of wear. We attempt to un- derstand these results in the framework of moving dislocations and their assistance to the mass transport among the dispersed lead particles. Ó 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Nano particles; Wear; Diffusion; Coarsening; Dislocation 1. Introduction Aluminium alloys containing uniform dispersion of micron-sized lead particles have shown improved fric- tion and wear behaviour [1–5]. There is also an increase in interest in the study of composites containing sub- micron particles of soft metals synthesized by nonequi- librium processing for tribological application [6,7]. Recent scientific literature [8,9] indicate considerable efforts in processing nanoscaled dispersoids of soft metals in various metallic matrices by rapid solidifica- tion and understanding the influence of these nanoscaled particles on properties. Following, an exploratory work [10,11], we present a detailed study of early stage friction and wear behaviour of binary aluminium alloys con- taining soft dispersion of lead particles of nanometric size. The investigation includes a detailed characteriza- tion of these particles before and after wear. The anal- ysis of the microstructure of the cross-section provides an insight into the deformation process of the embedded nano particles under low sliding velocity. 2. Experimental The alloy having a nominal composition of Al– 2.5at.%Pb was prepared by melting 99.99%Al and 99.99%Pb in an alumina crucible using an rf generator as the heating source, operated at a power of 20 kW. Subsequently the alloy was rapidly solidified using the melt spinning technique. The melt was kept at a tem- perature above the critical line of the miscibility gap to ensure homogeneity of the melt prior to spinning. An Ar overpressure of 20 kPa was used for ejecting the melt onto the surface of a copper wheel moving at a velocity of 24 m/s. The samples thus obtained were in the form of ribbons of thickness 80 lm and width of 2.5 mm. Preliminary phase identification of the samples was carried out by X-ray diffraction (JEOL model JDX 8030) using Cu Ka and Fe Ka (k ¼ 0:1541 and 0.1937 nm) * Corresponding author. Tel.: +91-802-932-678; fax: +91-803-601- 991. E-mail address: victoria@metalrg.iisc.ernet.in (V. Bhattacharya). 1359-6454/$30.00 Ó 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2004.01.020 Acta Materialia 52 (2004) 2293–2304 www.actamat-journals.com