Elucidating the Effect of MoS 2 on the Mechanical and Tribological Behavior of AA7075/Si 3 N 4 Composite
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Elucidating the Effect of MoS2 on the Mechanical and Tribological Behavior of AA7075/Si3N4 Composite Mir Irfan Ul Haq
, Ankush Raina, Ankush Anand, Sanjay Mohan Sharma, and Rajiv Kumar
(Submitted March 2, 2020; in revised form August 4, 2020; Accepted September 24, 2020) In the current work, a novel self-lubricating AA7075-based composite has been developed with silicon nitride (8 wt.%) as the ceramic reinforcement and varying MoS2 (0-6 wt.%) content by using stir casting method. The effect of solid lubricant (MoS2) addition on the microhardness, compression and microstructural behavior has been studied. Unidirectional sliding wear tests were carried out to study the effect of the reinforcement addition on the coefficient of friction and wear. The testing has been carried out at three different sliding speeds (1, 4 and 7 m/s) to elucidate the effect of sliding speed on the wear and friction behavior. The mechanical strength of the developed composites exhibited a decreasing trend with an increase in the MoS2 content. However, a 37% decrease in the COF was also observed with an increase in molybdenum disulfide (MoS2) content. With an increase in the normal load, COF exhibited an increasing behavior. The wear loss also exhibited an increasing trend with an increase in normal load as well as speed. The worn surface analysis exhibited a shift of wear mechanism from severe abrasion toward mild abrasion in the case of composites with higher content of MoS2. EDS also revealed the formation of mechanically mixed layer (MML) and oxide formation. The developed composites with better anti-friction properties have wide scope in sliding applications, particularly in automotive sector. Keywords
AA7075, aluminum, friction, lightweight materials, MoS2, self-lubricating composites, solid lubrication, stir casting, wear Si3N4
1. Introduction The increasing demands for sustainable (Ref 1) technologies have led to an increased focus on the research in the area of lightweight materials such as aluminum and magnesium. Aluminum in its pure form lacks good mechanical properties and hence is not structurally much applicable. Aluminum when alloyed with various elements such as zinc, magnesium, silicon exhibits better mechanical properties. AA 7075 being an alloy of aluminum with zinc as the primary alloying element exhibits excellent mechanical properties comparable with steels; however, it offers less resistance to wear (Ref 2). Friction and wear being intrinsic to various engineering applications, designers and material scientists are working on the development of materials with better mechanical properties along with good friction and wear properties. Due to the environmental, economic and technical disadvantages related to liquid lubrication, recently focus has shifted toward development of self-lubricating materials (Ref 3-5). In the case of selflubricating materials, solid lubricants such as graphite, calcium fluoride, barium fluoride have been tried; however, adding the softer solid lubricant phas
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