Mechanical properties and thermal stability of (NbTiAlSiZr)N x high-entropy ceramic films at high temperatures
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ARTICLE Mechanical properties and thermal stability of (NbTiAlSiZr)Nx high-entropy ceramic films at high temperatures Qiu-Wei Xing, Song-Qin Xia, and Xue-Hui Yan The State Key Laboratory of Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 10083, China
Yong Zhanga) The State Key Laboratory of Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 10083, China; and Beijing Key Laboratory for Magneto-Photoelectrical Composite and Interface Science, University of Science and Technology Beijing, Beijing 100083, China (Received 20 June 2018; accepted 4 September 2018)
High-entropy ceramic (HEC) films refer to the carbide, boride, oxide, or nitride films of the high-entropy alloy, which have potential applications under high temperatures. In this study, we fabricated the HEC NbTiAlSiZrNx films using magnetron sputtering under various deposition atmospheres. The phase structure evolution and the mechanical properties of three HEC films under high temperatures were investigated. The HEC films demonstrated good thermal stability as well as high hardness. After annealing for 24 h at 700 °C, the films remained in an amorphous phase without obvious crystallization, and the hardness of the films declined. Nanocrystallizations occurred in films deposited at a nitrogen flow rate of 4 sccm and 8 sccm after annealing for 30 min at 900 °C and exhibited an face-centered cubic structure. HEC NbTiAlSiZrNx films have potential applications as protective coatings under high temperatures.
I. INTRODUCTION
High-entropy alloys (HEAs), also known as multicomponent alloys, have been widely investigated due to their high strength and superior ductility.1 HEAs exhibit other interesting properties compared to conventional alloy systems, such as abnormal temperature dependence of impact toughness under cryogenic temperatures2 and high irradiation resistance.3,4 Some of the refractory HEAs remain excellent mechanical property under extremely high temperatures.5,6 For example, the yield stress of NbMoTaW and NbMoTaWV exceeds that of the traditional Ni-based superalloys (Inconel 718 and Haynes 230), with their working temperature above 800 °C.7 Recently, Zou et al.8 identified excellent mechanical properties and enhanced stability of HEA pillars under high temperatures. Compared to pure tungsten, the yield strength of NbMoTaW high-entropy films did not decline substantially after prolonged heat treatment (3 d at 1100 °C), confirming the high phase stability and mechanical properties of these films at high temperatures compared to pure metals. Aside from HEAs, bulk high-entropy oxides9,10 and high-entropy borides were also discovered recently. Carbide, boride, oxide, and nitride thin films of HEAs can be fabricated by reactive sputtering or laser-cladding a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.337 J. Mater. Res., Vol. 33, No. 19, Oct 14, 2018
technology. Yeh et al.11 defined these materials as highentropy ceramics (HEC), which usually posses
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