Fabrication of NiCoFeCrMn high-entropy alloy by mechanical alloying for high-temperature aviation engine bearings and investigation of its tribological wear performance

Abstract

In this study, a NiCoFeCrMn high-entropy alloy (HEA) intended for aviation engine bearing applications was produced by mechanical alloying; its tribological wear behavior was systematically investigated using the pin-on-disk method at room temperature (RT), 300, and 600 degrees C. Elemental powders with equal atomic ratios (99.9% purity) were mechanically alloyed in a high-energy planetary ball mill for 20 h, pressed under a pressure of 700 MPa, and subsequently sintered in an argon atmosphere. Comprehensive investigations of the tribological wear behavior of mechanically alloyed NiCoFeCrMn HEAs over the temperature range of 25-600 degrees C remain limited in the literature, and the present study aims to address this research gap. XRD analysis revealed the successful formation of a single-phase nanocrystalline FCC solid solution after 20 h of mechanical alloying, without any detectable secondary phases or intermetallic compounds. The microhardness decreased from 251 HV0.5 at RT to 210 HV0.5 (16.3%) at 300 degrees C and 170.8 HV0.5 (31.9%) at 600 degrees C, indicating a two-stage thermal softening behavior while retaining a substantial fraction of the initial hardness throughout the investigated temperature range. Tribological tests showed that increasing temperature significantly improved all performance indicators. Under both loading conditions, the highest coefficient of friction and wear rate were recorded at RT, whereas the lowest values were obtained at 600 degrees C. Under a 10 N load, the coefficient of friction decreased from 0.49 at RT to 0.29 at 600 degrees C (a 40.8% decrease), while the wear rate decreased from 1.42 & times; 10(-)3 mm3/N & centerdot;m at RT to 0.74 & times; 10(-)3 mm3/N & centerdot;m at 600 degrees C (a 47.9% decrease). Under a 20 N load, the coefficient of friction decreased from 0.57 at RT to 0.37 at 600 degrees C (a 35.1% decrease), and the wear rate decreased from 1.12 & times; 10(-)3 mm3/N & centerdot;m at RT to 0.60 & times; 10(-)3 mm3/N & centerdot;m at 600 degrees C (a 46.4% decrease). SEM-EDS, XRD, and cross-sectional analyses performed at RT, 300, and 600 degrees C revealed a temperature-dependent transition in the dominant wear mechanism. Adhesive and abrasive wear predominated at RT because of the low oxygen content and the presence of single-phase FCC wear debris. At 300 degrees C, an intermediate oxidation stage was observed, whereas at 600 degrees C, a stable Cr2O3/MnO protective tribofilm, confirmed by XRD and cross-sectional EDS analyses, formed on the wear surface, resulting in simultaneous reductions in both the coefficient of friction and the wear rate.