Optimization of Tribological Behavior of Mg-Wc Nanocomposites at Elevated Temperature

Optimization of Tribological Behavior of Mg-Wc Nanocomposites at Elevated Temperature

Sudip Banerjee, Suswagata Poria, Goutam Sutradhar, Prasanta Sahoo
DOI: 10.4018/IJSEIMS.2020010103
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The present investigation scrutinizes the role of wt.% of WC (0, 0.5, 1, 1.5 and 2%), operating temperature (50, 100, 150, 200 and 250°C) and load (20, 30 and 40N) on wear rate and coefficient of friction (COF) of Mg-WC nanocomposites. A multilevel full factorial design is considered to optimize the response variables. Mg-WC nanocomposites are synthesized through ultrasonic vibration assisted stir casting method. Tribological tests are performed in a pin-on-disk tribotester at dry sliding condition. Optical microscope and scanning electron microscope (SEM) are used to visualize the microstructural phases and distribution of reinforcements respectively. Main effect plots and interaction plots are analyzed to find the effect of selected parameters and their interactions. Analysis of variance (ANOVA) is also carried out for response variables to find the significant parameters. Linear regression equations are also generated to relate the output and input parameters. Worn surfaces are studied with the help of SEM images to examine the wear mechanisms.
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1. Introduction

Modern aviation and automotive industries are concerned on weight saving, emission reduction and fuel economy of vehicles. Lightweight structural materials like magnesium, aluminium etc. have been revolved into an inevitable solution of this concern due to their low density, good castability, good manufacturability (Hirsch & Al-Samman, 2013). Among these materials, magnesium possesses some advantages like light weight, melting temperature within a control range, better machinability, good castability and better manufacturability (Kulekci, 2008). As a consequence, magnesium shows improved fuel economy, less energy consumption and better productivity which are immensely important for automobile, aviation and electronic components. Hence significant amount of magnesium is expected to be used in recent years as structural material. However several typical technical issues like limited formability, poor strength at elevated temperature, anisotropic mechanical behavior below 200°C, poor tribological behavior at room and high temperature have hindered the application of commercially pure magnesium and magnesium alloys in several elevated temperature applications like engine parts (blocks, pistons and crank cases) (∼200°C), movable components and automatic transmissions of IC engines (∼175°C) and bearings of aviation systems (Pai et al., 2012). The above-mentioned limitations can be prevailed over either by evolving new alloys or by reinforcing hard ceramic particles in magnesium matrices (Pan et al., 2016). Typically, calcium, silicon, strontium or rare earth (RE) elements are used as alloying element. In previous literature, several alloy systems like Mg-Al-Si, Mg-Al-Ca, Mg-Al-Sr, Mg-Al-RE, Mg-Al-RE-Ca etc. are found (Mahmudi et al., 2011). Researchers have fabricated these alloys and examined their mechanical and tribological characteristics at elevated temperatures. Mazraeshahi et al. (2015) have used Si as alloying element to improve the mechanical behavior of magnesium. An et al. (2018) have studied the tribological behavior of Mg-3Al-0.4Si-0.1Zn in the temperature range of 50-200°C. Asl et al. (2010) have used misch metal as rare earth element and used it for alloying with Mg-Al-Zn alloy. They also studied the mechanical behavior and wear behavior of the developed alloy. Similarly, Nami et al. (2011) have examined the effect of Ca and rare earth element on the mechanical property and microstructural changes of AZ91 alloy. Mahmudi et al. (2011) have studied the effect of addition of rare earth on thermal stability, mechanical properties and microstructural properties of AZ91 magnesium alloy. Powel et al. (2001) have used Ca and Sr as alloying element and developed Mg-5Al-2Ca and Mg-5Al-2Ca-0.1Sr alloy to improve the high temperature mechanical behavior of the developed alloy compared to base Mg-Al alloy.

On the other hand, researchers have also used hard ceramic like SiC, Al2O3, TiB2, B4C, WC etc. for improving mechanical and tribological properties at room and elevated temperature (Dey & Pandey, 2015). Accordingly, Labib et al. (2018) have studied the hot hardness and shear punch test of Mg-SiC composite at elevated temperatures. Similarly, Hassan et al. (2008) have examined the elevated temperature tensile properties of Mg-1.1Al2O3 nanocomposite. Again, Labib et al. (2016) have also examined the dry sliding wear behavior of Mg-SiC composites at different loads and different operating temperature. Labib et al. (2016) have noticed that composites show lower wear rate than pure Mg at higher temperatures (100-200°C) while increased value of load shows transition of wear characteristics from mild to severe wear. Karuppusamy et al. (2019) have studied the wear performances of cryogenic treated AZ91-1.5WC nanocomposites.

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