Abstract
Owing to the brittleness of the body-centered cubic (BCC) structure and lack of self-lubrication, plasma-sprayed AlCoCrFeNi high-entropy alloy (HEA) coatings undergo severe abrasive wear, resulting in high friction and wear. In this study, the substrate surface temperature was increased (800 degrees C) to promote the phase transition from BCC to ductile FCC during spraying. As a result, the prepared AlCoCrFeNi HEA coating contained BCC and FCC phases, exhibiting a higher adhesive strength, lower friction coefficient and wear rate at room temperature (RT)-800 degrees C. In addition, the elevated substrate surface temperature enabled the transition of the low-temperature stable phase alpha-Bi2O3 to the high-temperature stable phase delta-Bi2O3. delta-Bi2O3 promoted the formation of low shear strength planes owing to its low interaction parameter and defect-fluorite structure with 25 % anionic vacancies similar to that of the Magn & eacute;li phase, which facilitated friction reduction in a wide temperature range. This study confirms that delta-Bi2O3 can effectively improve the anti-wear performance of the AlCoCrFeNi-Bi2O3 coating at RT, 200, 600 and 800 degrees C. However, at 400 degrees C, the low melting point and soft nature of the Bi2O3 weakened the mechanical strength of the coating and inhibited the construction of a solid and tough tribo-layer, resulting in a relatively high wear rate for AlCoCrFeNi-Bi2O3 coating. At 800 degrees C specifically, under the thermal coupling effect, delta-Bi2O3 migrated and aggregated on the worn surface with the oxidation product Al2O3 of the AlCoCrFeNi HEA matrix, and jointly promoted the formation of a compact and smooth tribo-layer with lubricating capability, which not only effectively reduced friction but also inhibited wear.
Keywords Plus：MECHANICAL-PROPERTIES，THERMAL-STABILITY
Published in SURFACE & COATINGS TECHNOLOGY，Volume476，10.1016/j.surfcoat.2023.130286；JAN 30 2024