Microstructure and Tribological Properties of AlCoCrFeNiTi 0.5 High-Entropy Alloy in Hydrogen Peroxide Solution
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INTRODUCTION
HIGH-CONCENTRATION hydrogen peroxide (HCP) is receiving renewed interest as a monopropellant and as the oxidizer for bipropellant systems, because it is nontoxic and storable, and has high density, low vapor pressure, and high specific heat.[1–3] HCP includes hydrogen peroxide concentrations ranging from 70 to 98 pct. In applications, the energy and oxygen released during decomposition of HCP are used for propulsion:[4] 2H2 O2 ðlÞ ! 2H2 O ðgÞ þ O2 ðgÞ DHr ¼ 2887:0 J g1 anhydrous HCP However, some parts of the hydrogen peroxide engine in the H2O2 solution are usually caused by excessive wear and the occurrence of premature failure, and incompatibility with structural materials will lead to decomposition of HCP in areas of the propulsion system, which gives rise to void energy production.[2,4] Pure aluminum and 1Cr18Ni9Ti stainless steel are acceptable compatible materials of H2O2, but both of them do not possess enough wear resistance.[5,6] Both wear and incompatibility seriously limit the applications and development of the H2O2 propulsion technique in the aerospace engine. Y. YU, Postdoctoral Student, T.B. ZHANG and H.C. KOU, Associate Professors, J.S. LI, Professor, and J. WANG, Lecturer, are with the State Key Laboratory of Solidification Processing at Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China. Contact e-mail: [email protected] W.M. LIU, Researcher, is with the State Key Laboratory of Solid Lubrication at Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China. J. LI, Researcher, is with the Wuhan Research Institute of Materials Protection, Wuhan 430000, People’s Republic of China. Manuscript submitted April 30, 2013. Article published online September 17, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
During the past decade, a new class of alloys, so-called high entropy alloys (HEAs), was proposed and developed. Compared with the conventional alloys based on one or two major elements, HEAs generally contain 5 to 13 principle elements at equimolar or nearequimolar atomic compositions with each elemental concentration between 5 and 35 at. pct, in which the formation of intermetallic phases can be prevented.[7–9] Therefore, these alloys predominantly consist of a mixture of simple solid solutions (face-centered-cubic (fcc), body-centered-cube (bcc), or mixed) due to high configurational entropy of mixing. It was reported that many HEAs possess a favorable combination of strength and ductility, high hardness, superior resistance to temper softening, oxidation, and corrosion.[10–12] The recent work of Duan et al.[13] indicates that AlCoCrFeNiCu alloy lubricated with 90 pct hydrogen peroxide solution preserves a lower friction coefficient than that with normal lubricant oil. These findings suggest that HEAs can show good resistance to wear in HCP. The research on the tribological performance of HEAs shows that constitution plays an important role in wear resistance. The adhesive wear behavior of AlxCoCrCuFe
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