Compositional disorder and sintering of entropy stabilized (Hf,Nb,Ta,Ti,Zr) B2 solid solution powders

Entropy-stabilized (Hf,Nb,Ta,Ti,Zr)B-2 solid solution powders produced by a carbo/boro-thermal reduction followed by solid solution formation were first analysed by synchrotron radiation x-ray diffraction, and their long range periodicity (i.e. lattice parameters) as well as the micro-strain intended as lattice disorder were quantitatively determined. A model to describe the micro-strain was proposed. The as-synthesized (Hf,Nb,Ta,Ti,Zr)B-2 solid solution powders were then hot-pressed at 2200 K and 50 MPa until near full densification was achieved. The hot-pressed material had a residual micro-porosity of 1.3 vol.% and consisted of a (Hf,Nb,Ta,Ti,Zr)B-2 ceramic matrix, 0.3-1 mu m grain size range, and of a residual 10 vol.% B4C particulate component, grain size in the range 0.2-2 mu m. B4C was a side product of the former synthesis and, after hot-pressing, remained trapped along the grain boundaries of the primary (Hf,Nb,Ta,Ti,Zr)B-2 solid solution ceramic matrix. Micro-hardness HV0.2 = 22.7 +/- 1.9 GPa for 1.96 N applied force was measured.