A recent paper reports a ductility at ambient temperature of about 50% for an Al-Fe-Co-Ni high-entropy alloy that yields at 670 MPa and work hardens to about 1.05 MPa. Science 373, 912-918 (2021). Such properties are more easily obtainable, on a commercial scale, in for example, twinning-induced plasticity steels.
Interesting paper showing that a degree of atomic ordering in an equiatomic CoCrNi alloy had no perceptible effect on the stress-strain curve. PHYSICAL REVIEW MATERIALS 5, 085007 (2021). The authors used the atom probe to establish a strange kind of ordering in which there is periodicity along but not . The insensitivity of the stress-strain curve implies either very weak ordering or a very small antiphase boundary energy which means that dislocations behave as if they are in a disordered system. Transmission electron microscopy of the dislocation structure would be revealing. The absence of superdislocations would imply a very low antiphase boundary energy.
A recent paper [MATERIALS SCIENCE AND TECHNOLOGY 37 (2021) 765] on the effect of aluminium content on Fe_1.25 Co Cr Ni_1.25 Al_x concludes that increasing aluminium (x=0.1, 0.25, 0.4) does not change the crystal structure from face-centred cubic. This could have been predicted precisely from the the Al/Ni ratio as explained during this lecture (30.11 minutes).
@47:11 At very small temperatures phononic contributations to heat capacity is neglible and therefore the measure heat capacity is dominated by the specific heat of electrons arising due to Pauli's exclusion principle (i.e. Fermi-Dirac statistics).
It should not be surprising that charging the CrMnFeCoNi alloy with hydrogen will embrittle it. The paper published in Int. Journal of Hydrogen Energy (doi.org/10.1016/j.ijhydene.2021.07.136). Totally expected, well established. What is surprising is that the very low diffusivity of hydrogen in face-centred cubic alloys of this kind (Int. Journal of Hydrogen Energy 45 (2020) 10227) is not taken into account because the penetration of hydrogen into the 1.2 mm thick samples will be of the order of micrometres into the surface. This is why, for example, the charging of TWIP steel with hydrogen is so difficult beyond a depth of more than a few micrometres. I suggest that there is no work needed to assess the hydrogen embrittlement of high-entropy fcc alloys without thinking of an application and all the other design parameters that must be optimised for that application.
A recent paper reports a ductility at ambient temperature of about 50% for an Al-Fe-Co-Ni high-entropy alloy that yields at 670 MPa and work hardens to about 1.05 MPa. Science 373, 912-918 (2021). Such properties are more easily obtainable, on a commercial scale, in for example, twinning-induced plasticity steels.
Interesting paper showing that a degree of atomic ordering in an equiatomic CoCrNi alloy had no perceptible effect on the stress-strain curve. PHYSICAL REVIEW MATERIALS 5, 085007 (2021). The authors used the atom probe to establish a strange kind of ordering in which there is periodicity along but not . The insensitivity of the stress-strain curve implies either very weak ordering or a very small antiphase boundary energy which means that dislocations behave as if they are in a disordered system. Transmission electron microscopy of the dislocation structure would be revealing. The absence of superdislocations would imply a very low antiphase boundary energy.
A recent paper [MATERIALS SCIENCE AND TECHNOLOGY
37 (2021) 765] on the effect of aluminium content on Fe_1.25 Co Cr Ni_1.25 Al_x concludes that increasing aluminium (x=0.1, 0.25, 0.4) does not change the crystal structure from face-centred cubic. This could have been predicted precisely from the the Al/Ni ratio as explained during this lecture (30.11 minutes).
@47:11 At very small temperatures phononic contributations to heat capacity is neglible and therefore the measure heat capacity is dominated by the specific heat of electrons arising due to Pauli's exclusion principle (i.e. Fermi-Dirac statistics).
Yes, like all metals.
@@bhadeshia123 Exactly, because these are free electrons. Therefore, the behaviour should not change be it a metal or an alloy..
It should not be surprising that charging the CrMnFeCoNi alloy with hydrogen will embrittle it. The paper published in Int. Journal of Hydrogen Energy (doi.org/10.1016/j.ijhydene.2021.07.136). Totally expected, well established. What is surprising is that the very low diffusivity of hydrogen in face-centred cubic alloys of this kind (Int. Journal of Hydrogen Energy 45 (2020) 10227) is not taken into account because the penetration of hydrogen into the 1.2 mm thick samples will be of the order of micrometres into the surface. This is why, for example, the charging of TWIP steel with hydrogen is so difficult beyond a depth of more than a few micrometres. I suggest that there is no work needed to assess the hydrogen embrittlement of high-entropy fcc alloys without thinking of an application and all the other design parameters that must be optimised for that application.