The Mechanical Properties of Si + and Pb + Implanted Al
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THE MECHANICAL PROPERTIES OF Si+ and Pb+ IMPLANTED Al P.B. MADAKSON Department of Mechanical Engineering, King's College, Strand, London, WC2R 2LS, England. ABSTRACT Commercially pure Al was implanted with 300 keV Si+ and 200 keV Pb+ to doses of between l0ol and 1017 ions/cm2 . Changes in friction, wear, oxidation and hardness were investigated. Silicon increased the hardness and wear resistance of Al and significantly decreased friction and the oxidation of the implanted surface. These changes were observed to be almost proportional to the implanted dose. The implantation of Pb+ resulted in a linear increase in hardness and a decrease in surface oxidation with dose. Friction decreased and wear resistance increased but the changes were not dose dependent. The implantation of Si+ did not significantly alter the distribution of impurities, such as Fe and Cu within the Al matrix, but Pb+ resulted in a diffusion of Fe to the implanted surface. Formation of precipitates was observed and the improvements in the surface properties studied are considered to result from precipitation hardening, which involves the impediment of dislocation movement by the precipitates during plastic deformation of the implanted Al. INTRODUCTION Silicon is always present as an impurity in Al and like lead it imparts fluidity in casting and welding. Lead is usually added to the cast aluminium to improve bearing properties. It producesonly very slight changes in the mechanical properties of Al [1]. The presence of Si impurities in cast aluminium gives high mechanical properties through the formation of precipitates. Vandelli [2] observed that a fine dispersion of silicon needles, evenly distributed within the Al matrix, gives maximum improvement in wear resistance. Similar observations were made by Sarker and Clarke [3]. The work of Okabayashi et al [4] suggests however that both the distribution and the content of Si in Al are important for large improvements in mechanical properties. Only lead had previously been implanted into aluminium. Thackery and Nelson [5] reported the formation of Pb precipitates after implantation of Al. The role of these precipitates on the mechanical properties of Al was not investigated. It is reported in this paper that implanted Pb+ and Si+ produce significant changes in the mechanical properties of Al. The hardness, friction and wear of the implanted Al were measured and compared with values from the unimplanted Al. The experimental method has been described elsewhere [6]. Changes in surface oxidation were studied by the Rutherford back-scattering (RBS) technique. Silicon and lead were implanted into Al at 300 keV and 200 kev respectively. RESULTS Figure 1 shows that Pb+ and Si+ significantly increase the hardness of aluminium. Silicon produces the maximum increase in hardness. The increase in hardness is almost proportional to the Si+ dose. Lead
Mat.
Res.
Soc. Symp. Proc.
Vol.
27
(1984)
Published by Elsevier Science Publishing Co.,
Inc.
644
implantation into Al only produces about 20% increase in har
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