Ti₃AlC_2−yN_y carbonitride MAX phase solid solutions with tunable mechanical, thermal, and electrical properties

Changing the N content in the Ti₃AlC_2−yN_y MAX phase solid solutions allows for the fine-tuning of their properties. However, systematic studies on the synthesis and properties of Ti₃AlC_2−yN_y solid solution bulks have not been reported thus far. Here, previously reported Ti₃AlC_2−yN_y solid solution bulks (y = 0.3, 0.5, 0.8, and 1.0) were synthesized via hot pressing of their powder counterparts under optimized conditions. The prepared Ti₃AlC_2−yN_y bulks are dense and have a fine microstructure with grain sizes of 6–8 μm. The influence of the N content on the mechanical properties, electrical conductivities, and coefficients of thermal expansion (CTEs) of the prepared Ti₃AlC_2−yN_y bulk materials was clarified. The flexural strength and Vickers hardness values increased with increasing N content, suggesting that solid solution strengthening effectively improved the mechanical properties of Ti₃AlC_2−yN_y. Ti₃AlCN (y = 1) had the highest Vickers hardness and flexural strength among the studied samples, reaching 5.54 GPa and 550 MPa, respectively. However, the electrical conductivity and CTEs of the Ti₃AlC_2−yN_y solid solutions decreased with increasing N content, from 8.93×10⁻⁶ to 7.69×10⁻⁶ K⁻¹ and from 1.33×10⁶ to 0.95×10⁶ S/m, respectively. This work demonstrated the tunable properties of Ti₃AlC_2−yN_y solid solutions with varying N contents and widened the MAX phase family for fundamental studies and applications.