Adjustment of Hardness of (CrFeMn)x(NiyAl)1−x, (y = 1,3 and x = 0.6,0.72,0.80) High Entropy Alloys by Deliberate Control of Intermetallic Phase Formation: Microstructural Evolution, Hardness and Dry-Sliding Wear Response

Abstract

In this work, the softening of the hard, NiAl containing, Cr–Fe–Mn–Al–Ni high entropy alloy system by the introduction of Ni3Al, an intrinsically ductile intermetallic compound, is reported. The alloys were prepared by vacuum arc melting and their phase formation prediction models were verified in terms of the actual presented microstructural features. X-ray analysis revealed the presence of NiAl and Ni3Al intermetallic compounds in each HEA system group. The microstructure of all six examined alloys in their as-cast condition consisted of two phases (NiAl-rich B2 and FeCr-rich A2) featuring various eutectic morphologies, while spinodal decomposition was evident in every case. The NiAl–Cr pseudo-binary phase diagram was used for the explanation of the solidification sequence in each alloy. In terms of mechanical properties, HRC hardness measurements showed that higher amounts of Ni3Al can lower the alloys’ hardness up to half its initial value. Finally, dry-sliding wear testing revealed an oxidation-delamination mode of material removal in both HEAs group, while the Ni3Al containing alloys also exhibited parts of abrasive wear mode. Hardness vs composition diagram. It can be seen that by adjusting the type and the extent of the intermetallic phase being formed (a—NiAl, b—Ni3Al), the hardness can be controllably modified within a range of 21 to 58 HRC. The related wear rates are also included