Fatigue Behavior of Medium Entropy Alloys AlCrFe₂Ni₂ and AlCrFe₂Ni₂Mo_0.1- A Comparison with Super Duplex Steel 1.4517

Abstract

In the present study the notched fatigue behavior of two multi-phase medium entropy alloys (MEAs) AlCrFe2Ni2 and AlCrFe2Ni2Mo0.1 was characterized by three-point-bending (3-PB), along with a super-duplex steel 1.4517 as a reference material. An analytical approach for characterizing the fatigue notch factor (kf), based on grain size analysis in combination with finite element modelling (FEM) was used, relating the theory of critical distances (TCD) to the grain size of the material. To validate the approach, for the reference steel, the fatigue notch factor was also determined experimentally by comparing the fatigue behavior of notched and smooth specimens, resulting in an experimentally determined fatigue notch factor (kf) ~ 1.07. The numerically and analytically estimated notch effects increase with decreasing average grain size and vary between ~ 1.07 for the coarse-grained reference material – in very good agreement with the experimental results – and ~ 1.35 for the much more fine-grained AlCrFe2Ni2Mo0.1 medium entropy alloy. Note that these values are significantly lower than the stress concentration factor (kt) ~ 1.58, associated with the notch geometry. Fatigue endurance limits were measured at a fatigue stress ratio R ~ 0.1 (unidirectional stress), but were converted to fatigue amplitudes at R = -1 (σa, R-1, fully reversed stress), to be able to make due comparisons with available literature data, by using the elliptical relationship. The resulting fatigue endurance limit amplitudes for specimens surviving at least 2E+06 cycles for a minimum of three tested samples and including notch effects are σa, R-1 ~ 508 MPa for the AlCrFe2Ni2 alloy, σa, R-1 ~ 540 MPa for the AlCrFe2Ni2Mo0.1 alloy modification and σa, R-1 ~ 400 MPa for the reference super-duplex steel, putting the analyzed MEAs into a very competitive position compared to Cobalt containing multi-phase high or medium entropy alloys as well as commercially available steels.