Tailoring the mechanical and tribological properties by regulating the heterogeneous microstructure of the Nb-doped AlCoCrFeNi high-entropy alloys
摘要
AlCoCrFeNi–xNb (x = 0, 1, 3, 5, 7, 9 wt.%) high-entropy alloys were fabricated via mechanical alloying–spark plasma sintering (MA–SPS) to clarify the composition-dependent regulation of precipitates, tensile response, and wear resistance by Nb. Nb promotes the precipitation of a Nb-rich Laves phase, Co(Ni,Fe,Cr)2Nb, whose volume fraction increases monotonically from 1.16% at 1Nb to 15.82% at 9Nb. The hardness increases nearly linearly with Nb, from 470.2 HV (0Nb) to 766.8 HV (9Nb). A compositional threshold is observed in tension: the ultimate tensile strength (UTS) rises from 955 MPa (0Nb) to a maximum of 1120.2 MPa at 1Nb, corresponding to a gain of 165.2 MPa (~ 17.3%) over the baseline with an elongation of 4.9%; when Nb ≥ 5 wt.%, both UTS and elongation decrease, reaching 215 MPa and 1.3% at 9Nb, consistent with crack initiation and rapid propagation along Laves-rich phase boundaries at high Laves fraction/connectivity. In sliding wear, 9Nb shows the lowest wear rate of 1.52 × 10–5 mm3/(N m), which is 2.56 times lower than that of 0Nb (3.89 × 10−5 mm3/(N m)). Wear track XPS further indicates a Nb2O5-dominated tribo-oxide film, supporting reduced material removal and a shift toward oxidation-assisted wear at high Nb.