Microstructural evolution and wear performance of the high-entropy FeMnCoCr alloy/TiC/CaF 2 self-lubricating composite c
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State Key Laboratory of Powder Metallurgy, Science and Technology on High Strength Structural Materials Laboratory, Central South University, Changsha 410083, People’s Republic of China a) Address all correspondence to this author. e-mail: [email protected] Received: 21 November 2018; accepted: 30 January 2019
The FeMnCoCr high-entropy alloy/TiC/CaF2 self-lubricating coatings were successfully prepared on a Cu–Zr–Cr alloy for continuous casting mold by laser cladding for wear-resistance. The intriguing finding was that the laser-cladded FeMnCoCr is mainly composed of face-centered cubic and hexagonal close-packed solid solution phases. During the cladding process, the FeMnCoCr/TiC or the FeMnCoCr/TiC/CaF2 mixed sufficiently with Cu matrix, while FeMnCoCr exhibited a spherical shape owing to being insoluble in Cu. The average hardness of the FeMnCoCr/TiC/CaF2 self-lubricating high-entropy alloy (HEA) coatings was twice that of the pure FeMnCoCr HEA coating. By addition of TiC, the friction coefficient and wear rate were decreased from 0.35 and 3.68 × 10−15 mm3/m to 0.27 and 3.06 × 10−15 mm3/m, respectively. When CaF2 was added, the friction coefficients and wear rate were decreased to 0.16 and 2.16 × 10−15 mm3/m, respectively, which was 54% lower than the pure FeMnCoCr HEA coating. The main wear mechanism of the FeMnCoCr coating is abrasive wear while that of the FeMnCoCr/TiC coating is abrasive and adhesion wear. But adhesion wear is dominant for the FeMnCoCr/TiC/ CaF2 coating.
Introduction In general, copper possesses many outstanding properties, such as excellent electrical and thermal conductivities, high ductility, and ease of manufacture [1]. Thus, Cu alloys are regarded as lead frame materials for integrated circuits, casting molds, and crystallizers in continuous casting [2] and important engineering materials such as electric contacts and commutators [3]. Nevertheless, it is worth noting that the mechanical properties of Cu alloys, such as low hardness and low wear resistance, do not meet the need of many practical applications. Surface coating is an effective route to overcome the shortcomings of copper components and provides a longer service life of coatings at reduced total cost. There are many ways to improve the mechanical properties of copper, including electroplating [3], thermal spraying [4], and infiltration techniques. Among them, thermal spraying is a highly effective approach for coating preparation. Hsu et al. studied the oxidation resistance
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of Ni0.2Co0.6Fe0.2CrSi0.2AlTi0.2 HEAs coating through thermal spraying [5]. However, the thermal spraying is unsatisfactory on metallurgical bonding. Laser cladding is one of the most efficient and economical ways for coating preparation, owing to the high cooling rates (103–108 K/s) which produces metastable phases by exceeding the solid-solubility limit beyond the equilibrium phase diagram with an excellent metallurgical bond to the substrate [6]. Thus, laser cladding has many advantages, such as high speed of heating an
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