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Recently multielements solid solution has shown significant improvement to the mechanical properties of parent MAX phases. Therefore, in this work, five elements with different radii were incorporated to check the effect on properties of MAX phases. (Nb0.8Ti0.05Zr0.05Mo0.05Hf0.05)4AlC3 (MAXHf) and (Nb0.8Ti0.05Zr0.05Mo0.05Ta0.05)4AlC3 (MAXTa) ceramics were successfully synthesized using the spark plasma sintering technique. The microstructure and elemental map analysis results further confirmed that the five transition metals were successfully solid soluted at the M‐sites of the hexagonal M4AlC3 unit cell. The mean elemental compositions for M‐site elements were achieved as Nb0.85Ti0.052Zr0.035Mo0.027Hf0.036 and Nb0.847Ti0.051Zr0.043Mo0.025Ta0.033 for MAXHf and MAXTa ceramics, respectively. The electrical and thermal conductivities of multielement solid solution MAX phases were decreased compared to pure Nb4AlC3. However, Mechanical properties were significantly increased with the solid solution of five transition metals. The fracture toughness, flexural strength, compressive strength and Vickers hardness (10 N) of MAXHf and MAXTa ceramics were achieved as 8.87 MPa m1/2, 448 MPa, 867 MPa, 6.5 GPa and 10.36 MPa m1/2, 557 MPa, 1039 MPa, 8.2 GPa, respectively. The enhanced mechanical properties suggest the effectiveness of the solid solution strengthening effect and provide new opportunities to further tailor the mechanical properties of the MAX phase ceramics. [ABSTRACT FROM AUTHOR]

The first 413-phase entropy-enhanced (Nb 0.8 Ti 0.05 Ta 0.05 V 0.05 M 0.05) 4 AlC 3 (M = Hf, Zr) (EEMAX Hf and EEMAX Zr) ceramics were successfully consolidated by spark plasma sintering (SPS) using Nb, Ti, Ta, V, Zr, Hf, Al and graphite as initial materials. The formation of solid solution with five transition metals at the M sites of hexagonal M 4 AlC 3 unit cell was confirmed by elemental analyses. Compared with pure Nb 4 AlC 3 , both the electrical and thermal conductivities of the entropy-enhanced ceramics showed a slight decrease, which is attributed to the lattice distortion and the increasing lattice defects that prevents the transfer of electrons and phonons. On the other hand, the mechanical properties of entropy-enhanced ceramics were greatly enhanced compared to pure Nb 4 AlC 3. The measured fracture toughness of EEMAX Hf and EEMAX Zr ceramics were 8.2 MPa·m1/2 and 10.0 MPa·m1/2, respectively, which were increased by 18.8% and 44.9% compared to Nb 4 AlC 3. The compressive strength of EEMAX Hf and EEMAX Zr ceramics were 987 MPa and 1187 MPa, respectively, being 92.0% and 130.9% higher than that of Nb 4 AlC 3 , respectively. EEMAX Hf and EEMAX Zr ceramics also possessed the higher Vickers hardness of 6.8 GPa and 7.4 GPa, respectively. [ABSTRACT FROM AUTHOR]