Dry sliding wear response of some bearing alloys as influenced by the nature of microconstituents and sliding conditions
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I.
INTRODUCTION
THERE exist a number of alloys which can be used for a variety of tribological and other engineering applications.[1–7] Sliding of one component over/against the other occurs in many situations, bush bearings being one of the important ones.[1–7] In general, leaded-tin bronzes are widely used in bush-bearing applications[1,3,4–6] while aluminum bronzes are also used under specific service conditions.[5] Zinc-based alloys have been found to be cost- and energyeffective substitutes to the bronzes in various sliding wear applications.[1–3,6,7] From microstructural considerations, the conventional bronze alloys are quite different from one another. For example, the leaded-tin bronzes contain a considerable quantity of the lubricating phase, lead; the element increases the crack sensitivity of the alloy under specific conditions of sliding.[8,9] The aluminum bronzes do not contain any lubricating microconstituent but possess very good thermal stability. Finally, in the case of zincbased alloys, the major microconstituent (i.e., zinc) is lubricating in nature,[10] but the alloys suffer from poor elevated-temperature properties.[2] It may be mentioned that the sliding wear response of materials depends very much on their microstructural features in terms of lubricating properties, crack sensitivity, and thermal stability. In fact, the predominance of the factors under a specific sliding condition essentially controls the wear behavior of the materials. Thus, sliding conditions are the ones to govern the wear response of the materials. Available information indicates that although the sliding wear behavior of the leaded-tin and aluminum bronzes and zinc-based alloys has been studied to some extent,[8–22] yet the role of their microstructural characteristics on the sliding wear response of the alloys has been investigated to a limited extent[8,9,11,12,15–20] in spite of their great significance. In view of this information, an attempt has been made in this study to examine the influence of the role of various microconstituents of a leaded-tin bronze, an aluminum
bronze, and a zinc-based alloy on their sliding wear response under varying conditions of applied pressure and speed. Mechanical properties of the alloys have also been correlated with their wear properties. II.
EXPERIMENTAL
A. Alloy Preparation Alloys (Table I) were prepared by solidifying in the form of 20-mm-diameter, 150-mm-long cylindrical castings using permanent molds. Elements used for preparing the alloys had purity levels above 99.95 pct. B. Microstructural Characterization Microstructural studies of the alloys were carried out using a Leitz (Wetzlar, Germany) optical microscope. The specimens (20-mm diameter, 15-mm height) were metallographically polished and etched. Bronzes were etched with potassium dichromate solution, while dilute aqua regia was used for etching the zinc-based alloy. C. Measurement of Mechanical Properties Hardness of specimens was measured using a Vickers hardness tester at an applied load of 15 kg. An Instron un
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