The big advantage of refractory high entropy alloys (RHEAs) is their strength at high
temperatures, but their big disadvantage is their brittleness at room temperature,
which prevents their machining. There is a great need to classify the alloys in terms
of brittle-ductile (B-D) properties, with easily obtainable ductility indices (DIs)
ready to help design these refractory alloys. Usually, the DIs are checked by representing
them as a function of fraction strain, ε. The critical values of DI and ε divide the
DI—ε area into four squares. In the case of a successful DI, the points representing
the alloys are located in the two diagonal opposite squares, well separating the alloys
with (B-D) properties. However, due to the scatter of the data, the B-D separation
is not perfect, and it is difficult to establish the critical value of DI. In this
paper, we solve this problem by replacing the fracture strain parameter with new DIs
that scale with the old DIs. These new DIs are based on the force constant and amplitude
of thermal vibration around the Debye temperature. All of them are easily available
and can be calculated from tabulated data.
