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Research Papers: Friction & Wear

Enhancement of Wear Resistance of Copper With Tungsten Addition (20wt%) by Powder Metallurgy Route

[+] Author and Article Information
Poulami Maji, R. K. Dube

Department of Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, IIT Kanpur, Kanpur 208016, Uttar Pradesh, India

Bikramjit Basu1

Department of Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, IIT Kanpur, Kanpur 208016, Uttar Pradesh, Indiabikram@iitk.ac.in

1

Corresponding author.

J. Tribol 131(4), 041602 (Sep 23, 2009) (9 pages) doi:10.1115/1.3204776 History: Received February 13, 2009; Revised July 17, 2009; Published September 23, 2009

Copper–tungsten composite materials are developed for applications such as electrical contacts, resistance electrodes, and contact tips in welding guns as well as for components requiring higher wear resistance. In addition to the aspect of improved performance, it is scientifically interesting to assess the tribological properties, and therefore the objectives of the present work include, to determine the role of W additions in improving the fretting wear resistance of Cu for electrical applications, to determine the optimum concentration for W additions, and to identify the mechanisms responsible for fretting wear improvements. In addressing these issues, a planned set of fretting wear tests were conducted on powder metallurgically processed Cu–W composites (maximum W content of 20wt%) against steel counterbody under varying load (up to 10 N) for 10,000 cycles. It has been observed that at lower loads of 2 N, the coefficient of friction (COF) recorded was 0.9 for the Cu20wt%W/steel, whereas it was 0.85 for a pure Cu/steel couple. Under similar operating conditions with the increase in load, the COF decreases to 0.5 at 10 N load, irrespective of the composition of the Cu–W composite. Furthermore, the incorporation of 5wt%W has reduced the volumetric wear loss by 4–6 folds in comparison to unreinforced Cu. The addition of even higher percentage of W has led to increase its wear resistance by 10 folds. Under the investigated conditions, the wear rate systematically decreases with the increase in load for all the tested Cu–W composites. Based on the topographical observation of worn surfaces, it is observed that wear mechanisms for the Cu and Cu–W composites are tribochemical wear, adhesive wear, and abrasive wear. The incorporation of harder W particles (5wt% or more) help in abrading the steel ball and in forming a dense tribolayer of FexOy, which effectively reduces wear rate and hence, increases wear resistance of the Cu–W composite surface in reference to unreinforced Cu.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparative XRD patterns of initial starting powders, milled powders, and powder metallurgically processed Cu–W compacts of a Cu–20 wt % W composition prepared by the repeated pressing-sintering route

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Figure 2

SEM micrograph (unetched) of Cu–20 wt % W composite compacts used as flat material in our fretting experiments

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Figure 3

The evolution of frictional behavior for the Cu–20 wt % W composite against bearing steel under the selected fretting condition of varying normal load (2N, 6N, and 10N) and test duration of 10,000 cycles with a constant frequency of 8 Hz and constant displacement stroke of 100 μm

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Figure 4

The variation in wear volume with the hardness of a Cu–W compact is shown when fretted under varying normal load (2N, 6N, and 10N). Fretting conditions: 8 Hz frequency, 100 μm sliding distance, test duration of 10,000 cycles, and counterbody steel ball (ϕ10 mm).

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Figure 5

The variation in specific wear rate of Cu–W composites with tungsten content. The fretting conditions are the same as those mentioned in Fig. 4.

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Figure 6

(a and b) SEM images of the overview of the worn surface on a pure/unreinforced Cu. The evidence of agglomerated wear debris particles can be seen in (c) and (d). EDS compositional analysis of the wear debris particle is presented in the inset. The fretting conditions are the same as those mentioned in Fig. 4.

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Figure 7

(a) SEM images of the overview of the worn surface on the Cu–5 wt % W composite. (b) The detailed views of worn surfaces. The fretting conditions are the same as those mentioned in Fig. 4.

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Figure 8

SEM images of the overview of the worn surface on the Cu–10 wt % W composite. The detailed views of worn surfaces (b and c) are also shown. EDS compositional analysis of the worn surface is presented in the inset. The fretting conditions are the same as those mentioned in Fig. 4.

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Figure 9

(a and b) SEM images of the overview of the worn surface on the Cu–20 wt % W composite at respective load. The detailed views of worn surfaces (c and d) at respective load are also shown. The evidence of coarse wear debris particles can be seen in (e). EDS compositional analysis of the worn surface or wear debris particle is presented in the inset. (f) SEM images of the worn scar on the steel counterbody against the Cu–20 wt % W composite overview. EDS analysis of the worn surface on the ball is presented in the inset. The fretting conditions are the same as those mentioned in Fig. 4.

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Figure 10

Schematic diagram of the various stages of the wear of Cu–W composites during fretting against steel

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