Tribological properties of NiAl matrix composite coatings synthesized by plasma spraying method
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Gaoa) State Key Laboratory for Mechanical Behaviour of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
Minmin Han, Hongjian Guo, Junhong Jia,b) and Wenzhen Wang State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China
Haitang Deng Institute of Design, Shaanxi Huanghe Group CO., LTD., Xi’an 710043, People’s Republic of China (Received 6 January 2017; accepted 30 March 2017)
The NiAl matrix composite coatings containing silver and molybdenum were prepared by atmospheric plasma spraying and their tribological properties were investigated in details from 25 to 900 °C. The X-ray diffraction (XRD), micro-Raman, scanning election microscopy (SEM) and transmission election microscopy (TEM) were used to analyze the composition and microstructure of composite coatings. The X-ray diffraction (XRD) results shown that molybdenum and silver were exist in single-phase, but not alloyed in composite coatings. The addition of silver could effectively improve the tribological properties of composite coatings at the wide range of temperature. The silver, nickel and molybdenum could occur the tribo-chemical reaction and form silver molybdates and nickel molybdates lubricating films inside the wear track of composite coatings at high temperature. The friction process promoted the formation of the silver molybdates. The silver molybdates, nickel molybdates and NiO were the main components in composite coatings at high temperature, which could effectively improve tribological properties of composite coatings.
I. INTRODUCTION
In recent years, the high-temperature self-lubricating metal matrix composite coatings have a wide and promising applications in several fields, such as auto-motive, nuclear power industries and aerospace.1–6 NiAl intermetallic compounds are considered to be the promising materials for high temperature applications due to the high melting point (Tm 5 1638 °C), high thermal conductivity, as well as excellent oxidation and corrosion resistence at high temperature.7–11 Graphite and molybdenum disulfide usually act as solid lubricants to improve the tribological properties of the composities.2,12–15 However, these solid lubricants would be oxidized or decomposed in air and lose their lubricating effects above 500 °C.2 It is essential to search efficient lubricants for high-temperature selflubricating coating in wide temperature range.2 Silver Contributing Editor: Jürgen Eckert Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.136
could decrease the friction coefficients and wear rates of composites and provide the excellent lubrication below 400 °C due to a large diffusion coefficient and low shear strength on the worn surface in the process of sliding.16–20 H. Zhou et al.16 prepared the NiMoAl–Cr3C2–Ag composite coatings by high velocity oxy-fuel (HVOF) spraying and demonstr
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