Elsevier

Wear

Volume 297, Issues 1–2, 15 January 2013, Pages 1045-1051
Wear

Tribological properties of AlCoCrFeNiCu high-entropy alloy in hydrogen peroxide solution and in oil lubricant

https://doi.org/10.1016/j.wear.2012.11.014Get rights and content

Abstract

Pin-on-disc tests to investigate the tribological behavior of AlCoCrFeNiCu high-entropy alloy under lubrication conditions with 90% hydrogen peroxide solution and lubricant oil, respectively, were performed. The study demonstrates that the AlCoCrFeNiCu high-entropy alloy lubricated correspondingly with lubricant of 90% hydrogen peroxide solution (hereafter termed hydrogen peroxide lubricant) and lubricant oil significantly improves its friction and wear-resistance properties. Results showed that the friction coefficient, after a grinding stage, of the rubbing pair was lower than that with normal lubricant oil. The AlCoCrFeNiCu alloy in the lubricant with 90% hydrogen peroxide solution and lubricant oil exhibits a high resistance to wear. Analysis of the worn surface revealed that the AlCoCrFeNiCu high-entropy alloy lubricated with the hydrogen peroxide lubricant exhibited signs of inhomogeneous polishing oxidation and abrasive wear, with the wear mechanism changing with sliding distance, while the rubbing pair in normal lubricant oil is mainly dominated by abrasive wear.

Highlights

► Tribological behavior of alloys in 90% H2O2 and lubricant oil were studied. ► These two lubricants improve alloys friction and wear-resistance properties. ► The friction coefficient of pair in 90% H2O2 was lower than that in lubricant oil. ► The wear mechanism exhibited sign of inhomogeneous under these two conditions.

Introduction

The demand of metallic alloys with superior mechanical and functional properties remains high in aerospace industry. Typical research for a strategic approach to synthesize stable, multi-component, high-temperature high-entropy alloys (HEAs) can be seen in Refs. [1], [2], [3], [4]. The HEAs are supposed to maximize their configurational entropy of a certain multi-component solid solution phase so that their disordered solid solution phases relative to possible intermetallic phases can be adequately stabilized by the entropy of mixing condition [4]. Constitution of such high-entropy alloys (HEAs) results in a new type of metallic alloys structurally characterized with high hardness, high resistance to wear and corrosion, and high resistance to temperature softening and oxidation, which is particularly superior to high-temperature applications [5]. Usually, high-entropy alloys (HEAs) are composed of more than five metallic elements with individual concentration ranging between 5 and 35 at%, and the elements are either in equal or near-equal atomic ratios so as to facilitate the formation of solid solution phases in bcc and fcc crystal structure [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. Study [18] indicated that the excellent physical properties of such HEAs belonged to a class of materials favorable for the use in engines of aircraft rocket operating in hydrogen peroxide solution.

Available literature [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29] is mainly focusing on the use of HEAs in their microstructure, mechanical properties, and ageing behaviors, etc. Studies on their tribological performance [30], [31], [32], especially their behaviors in hydrogen peroxide solution, are still rather lacking. Hsu [30] studied the effect of iron content on wear behavior of AlCoCrFexMo0.5Ni alloys, and showed: (i) the declination of wear resistance with increase of Fe content and (ii) the major wear mechanism of the HE alloy to be mainly abrasion. Chuang [31] studied the adhesive wear behavior and mechanism of a series of AlxCo1.5CrFeNi1.5Tiy high-entropy alloys with different Al and Ti contents and compared them with those of the conventional wear-resistant steels SUJ2 and SKH51. It was found that the performance of Co1.5CrFeNi1.5Ti and Al0.2Co1.5CrFeNi1.5Ti alloys were at least two folds better than that of conventional wear-resistant steels with similar hardness. Wu et al. [32] investigated the adhesive wear behaviors of AlxCoCrCuFeNi alloys with different aluminum contents. They found that the wear mechanism changed from delamination mode to oxidative mode, and their wear coefficient decreased with the increase of aluminum content. However, knowledge of the tribological properties of AlCoCrFeNiCu rubbed against Si3N4 under hydrogen peroxide solution is still rather lacking. Hence, the wear mechanism of AlCoCrNiCu under this lubrication medium yet remains in mist.

This work was initiated with an objective to reveal the tribological properties of AlCoCrFeNiCu against Si3N4 with different conditions of oil lubrication and hydrogen peroxide solution, respectively. It also examined the effect of environment on its frictional performance, specifically on its friction coefficient. Analysis of different modifications of the contacting surface and their correspondingly possible influence on the tribological behaviors of BMGs was conducted. Finally, their relevant wear mechanisms under different conditions were investigated and analyzed.

Section snippets

Processing of the AlCoCrCuFeNi high-entropy alloy and the counterpart

The corresponding commercial-pure metals, with individual purity beyond 99 wt% and nominal composition, were arc-melted and mixed in a Ti-gettered high-purity argon atmosphere for the preparation of the anticipated AlCoCrCuFeNi alloy ingots. These ingots were at least re-melted thrice under a highly vacuum condition so as to improve their homogeneity. The homogeneous melt was then suction-cast in a water-cooled copper mold to form Φ8×70 mm solid cylindrical ingots. These ingots are the as-cast

Friction and wear properties

As friction coefficient (μ) is an important factor to evaluate the tribological behaviors of a rubbing pair, the variation of such a variable vs. sling time (t) for the AlCoCrFeNiCu/Si3N4 rubbing pairs under 90% hydrogen peroxide solution and lubricant oil conditions, respectively, is shown in Fig. 3(a). Significantly different characteristics can be identified from those under 90% hydrogen peroxide solutions to those under lubricant oils. Under lubricant oil condition, friction coefficient

Conclusions

Results of the present study have confirmed that the tribological properties of AlCoCrFeNiCu high-entropy alloy are influenced by its environmental medium. AlCoCrFeNiCu/Si3N4 pair under lubricant oil condition exhibited a low value of friction coefficient during the whole test procedure, and its counterpart under 90% hydrogen peroxide solution gave an even lower friction coefficient when it reached at a near steady stage. Furthermore, higher resistance to wear was observed under the lubricant

Acknowledgments

The authors are grateful to the National Scientific and Technical Project of China for financial support (Contract no. 2013CB632303). The authors would also like to thank Assistant Engineer, Mr. Hu Chengping, for performing the experiments.

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