A DFT exploration of the stabilities, physical properties, and tensile strength of new synthesized Nb2AC (A=Ni and Co) MAX phases

Based on first-principles calculations, this study explored the structural stability, elastic anisotropy, tensile strength, and the mechanical, electronic, and thermodynamic properties of the newly synthesized MAX phases Nb 2 NiC and Nb 2 CoC. It has been found that these compounds are thermodynamically and mechanically stable, exhibit metallic conductivity, and possess ductile nature. The ultimate tensile strengths of Nb 2 NiC and Nb 2 CoC depend on their crystallographic directions, specifically [0001] and [112̄0]. In the [0001] direction, Nb 2 CoC has a tensile strength of about 36.63 GPa at a strain of 26%, compared to Nb 2 NiC, which has a tensile strength of 31.70 GPa at a strain of 24%. In the [112̄0] direction, Nb 2 CoC exhibits a tensile strength of around 23.29 GPa at a strain of 12%, while Nb 2 NiC has a tensile strength of approximately 18.51 GPa at an strain of 8%. Both Nb 2 CoC and Nb 2 NiC demonstrate significant elastic deformation before reaching their ultimate tensile strengths, indicating good ductility. It is noteworthy that Nb 2 NiC is less elastic than Nb 2 CoC in both the [0001] and [112̄0] directions, as the elastic constants of Nb 2 CoC are comparatively higher than those of Nb 2 NiC. Furthermore, the estimated thermal parameters show that these compounds exhibit a relatively low Debye temperature, a high melting point, low minimum thermal conductivity, and thermal expansion coefficient values that are similar to those of well-established thermal barrier coating (TBC) materials such as Al 2 O 3 , LaPO 4 , and TiO 2 . Consequently, the newly synthesized MAX phases Nb 2 NiC and Nb 2 CoC are promising candidates for TBC applications. • Conducted calculations to determine the stability, elastic constants, hardness, and thermal properties. • evaluated the thermodynamic stability of Nb 2 AC (A=Ni and Co) MAX phases based on their decomposition into a set of competing phases. • Generated a plot of the density of states (DOS). • Calculated velocities and Debye temperature. • Calculated polycrystalline elastic moduli.