Ti ₃AlC _{2− <i>y</i>}N _<i>y</i> carbonitride MAX phase solid solutions with tunable mechanical, thermal, and electrical properties

Changing N content in Ti₃AlC_2-yN_y MAX phase solid solutions allows for 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 so far. Here, previously unreported Ti₃AlC_2-yN_y solid solution bulks (y=0.3, 0.5, 0.8, and 1.0) were synthesized by hot pressing of their powder counterparts under optimized conditions. The prepared Ti₃AlC_2-yN_ybulks are dense and have a fine microstructure with grain sizes of 6-8 μm. The influence of N content on the mechanical properties, electrical conductivities, and coefficients of thermal expansion (CTEs) of the prepared Ti₃AlC_2-yN_y bulks has been clarified. Flexural strength and Vickers hardness values increased with increasing N contents, suggesting that solid solution strengthening is effective in improving the mechanical properties of Ti₃AlC_2-yN_y. Ti₃AlCN (y=1) showed 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 Ti₃AlC_2-yN_y solid solutions decreased with increasing N content, from 8.93´10^-6 K^-1 to 7.69 ´10^-6 K^-1，and 1.33´10⁶ S/m to 0.95´10⁶ S/m, respectively. This work demonstrates the tunable properties of Ti₃AlC_2-yN_y solid solutions with varying N contents, and also widens the member of MAX phase family for fundamental studies and applications.

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