First report on cold-sprayed AlCoCrFeNi high-entropy alloy and its isothermal oxidation
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FOCUS ISSUE
NANOCRYSTALLINE HIGH ENTROPY MATERIALS: PROCESSING CHALLENGES AND PROPERTIES
First report on cold-sprayed AlCoCrFeNi high-entropy alloy and its isothermal oxidation Ameey Anupam1,a) , S. Kumar2, Naveen M. Chavan2, Budaraju Srinivasa Murty1 Ravi Sankar Kottada1,b)
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1
Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600 036, India Centre for Engineered Coatings, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500 005, India a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] 2
Received: 15 September 2018; accepted: 22 January 2019
Cold-sprayed high-entropy alloy (HEA) coatings have been generated for the first time. Mechanically alloyed (MA) AlCoCrFeNi powder was chosen as feedstock, owing to the extensive literature on this alloy. Coatings were synthesized under various gas temperature and pressure conditions. Isothermal oxidation was conducted at 1100 °C for 25 h on the coating cold-sprayed at 400 °C and 10 bar on a Ni-base superalloy substrate. The assprayed coating retained the MA phases and formed a protective alumina layer upon oxidation. An interdiffusion zone at the interface and unanticipated Mo diffusion from the superalloy substrate into the coating were observed after oxidation. A comprehensive characterization at the coating–substrate interface suggests that diffusion in HEAs is not sluggish. The factors governing the coating’s oxidation are elucidated, and a plausible oxidation mechanism is discussed. These studies are aimed at developing oxidation-resistant HEA coatings for potential applications at high operating temperatures.
Introduction High-entropy alloys (HEAs) or multi-principal element alloys are a relatively recent category of materials wherein the principal constituent elements are added in equimolar or near equimolar concentrations [1, 2, 3, 4]. Nearly 15 years of research on various such alloys has generated a wealth of data and understanding of their alloying behavior and structure– property relationships. Notably, the AlCoCrFeNi family of alloys has been studied extensively. Information on phase evolution in equiatomic AlCoCrFeNi [5], via different processing routes (both liquid and powder metallurgy) [6, 7, 8, 9, 10, 11], their corresponding mechanical properties (both in compression and in tension) [12, 13, 14, 15, 16], their oxidation behavior [17, 18] as well as their tribological properties [19] is well documented in the literature. Promising reports on HEA nitride coatings [20, 21] and HEA compositions outshining commercial alloys’ oxidation resistance [22] have triggered the community’s interest in the coating aspects of HEAs and the possibility of considering them for potential commercial applications. One such potential application is as a bond coat
ª Materials Research Society 2019
in thermal barrier coating systems (TBCs) employed in jet engines. The role of bond coats in TBCs is primarily to prot
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