Ti3AlC2−yNy carbonitride MAX phase solid solutions with tunable mechanical, thermal and electrical properties

Ti₃AlC₂ as a representative MAX phase not only has a unique nano-layered crystal structure, but also possesses a combination of attractive properties of metals and ceramics. To further improve its properties, solid solution design as an effective strategy has been generally adopted.

Previous studies have confirmed that substituting C with N to form X-site MAX solid solution, such as Ti₂AlC_1−yN_y, can achieve solid solution strengthening and property modulation. Therefore, it is reasonable to believe that Ti₃AlC_2−yN_y solid solutions with varying N contents can possess desirable and tunable properties. However, such properties have not been confirmed by experimental results, which may be due to the difficulties in synthesizing dense Ti₃AlC_2−yN_y solid solutions with high-purity. For instance, the formation region of Ti₃AlCN in the Ti-Al-C-N quaternary phase diagram is relatively narrow and often accompanied by intermediate phases such as TiN, TiC, Ti₂AlN, and Ti₂AlC. In addition, theoretical work indicated that the stability of Ti₃AlC_2−yN_y decreased as more C atoms were replaced by N atoms.

Recently, the team led by Professor Shibo Li from Beijing Jiaotong University reported on the preparation and properties of Ti₃AlC_2-yN_y MAX solid solutions for the first time. By optimizing the hot pressing conditions, they successfully synthesized a series of dense Ti₃AlC_2−yN_y (y = 0.3, 0.5, 0.8, and 1.0) samples and investigated their composition, mechanical, thermal, and electrical properties. This work demonstrates the tunable properties of Ti₃AlC_2−yN_y solid solutions with varying N contents, and broadens the fundamental research and applications of MAX phase materials.

The team published their work in Journal of Advanced Ceramics on September 25, 2024.

“In this work, we successfully synthesized Ti₃AlC_2-yN_y (y = 0.3, 0.5, 0.8, and 1.0) dense solid solutions by hot-pressing of Ti, AlN, Al, and C powder mixtures under optimized conditions. Rietveld refinement of XRD data indicated that the high purity of the prepared Ti₃AlC_2−yN_y was approximately 97% to 98%. ” said Shibo Li, professor at Beijing Jiaotong University (China), a senior expert whose research interests focus on MAX and MAB phases, and 2D MXenes and MBenes.

“The replacement of C by N in Ti₃AlC_2−yN_y leads to a continuous decrease in a- and c-lattice parameters (a- and c-LPs). Lattice parameters have a significant impact on the physical properties of materials. Therefore, the continuous changes in a- and c-LPs inevitably affect the properties of Ti₃AlC_2−yN_y, such as theoretical density, thermal expansion, and electrical conductivity.” said Shibo Li.

The three-point bending test demonstrated that the flexural strengths of the solid solution samples are relatively higher than that of Ti₃AlC₂ (360 MPa). The flexural strength significantly increased from 424 to 550 MPa as y increased from 0.3 to 1.0. The measured Vickers hardness values increased from 3.3 to 5.54 GPa as y changed from 0 to 1.0. “Lattice distortion retards the movement of dislocations during the plastic deformation of Ti₃AlC_2-yN_y under compressive stresses and thus improves their mechanical properties. Solid solution strengthening is the main mechanism for improving the mechanical properties of Ti₃AlC_2-yN_y materials.” said Weiwei Zhang.

The thermal expansion test demonstrated that the coefficients of thermal expansion (CTEs) of Ti₃AlC_2−yN_y increased with increasing temperature in the temperature range of 25–900 °C. The average CTEs of Ti₃AlC_2−yN_y (y = 0, 0.3,0.5, 0.8, and 1.0) were 9.47×10⁻⁶, 8.79×10⁻⁶, 8.93×10⁻⁶, 8.37×10⁻⁶, and 7.69×10⁻⁶ K⁻¹, respectively. “It is well known that the CTEs of MAX phases are dependent on bonding (including bond lengths and types). Strong bonding or short bond lengths are responsible for the low CTEs.” said Weiwei Zhang.

The electrical conductivities of Ti₃AlC_2−yN_y with different N concentrations were measured at room temperature. The electrical conductivity linearly decreased from 1.48×10⁶ to 0.95×10⁶ S/m as the y value increased from 0 to 1.0. “The electrical conductivity linearly decreases with increasing N concentration, mainly due to the formation of lattice distortion and defects such as vacancies and dislocations induced by the solubility of N in Ti₃AlC_2−yN_y. Lattice distortion alters the motion path of electrons and scatters the transmission of electrons, thus leading to a decrease in the electrical conductivity. In addition, vacancies and dislocations hinder electron transport, thereby reducing the electrical conductivity of materials.” said Guoping Bei.

Ti₃AlC_2−yN_y solid solutions with tunable properties are attractive for future applications. Li and Bei suggested that future work will be performed to study the high-temperature properties of Ti₃AlC_2−yN_y solid solutions and to promote their applications in high-temperature environments.

Other contributors include Weiwei Zhang, Xuejin Zhang, Xiachen Fan from the School of Mechanical, Electronic and Control Engineering at Beijing Jiaotong University in Beijing, China; Shukai Fan, Guoping Bei from the Porcelain Fuchi High Tech Nano Materials Co., Ltd in Suzhou, China.

This work was supported by the Fundamental Research Funds for the Central Universities (Nos. 2023YJS061 and 2023JBZY019).

About Author

Shibo Li, PhD, Professor, is now working at Beijing Jiaotong University. His research interests focus on the synthesis and characterization of ternary layered MAX and MAB phases, 2D MXenes and MBenes, crack healing of advanced ceramics, radar/infrared integrated stealth materials, and applications of advanced materials in high seed railway.

In recent years, he has charged and participated in various projects funded by the National Natural Science Foundation of China, 863, 973 projects, international cooperation, and other ministries and commissions. He has published over 160 academic papers in journals such as Carbon Energy, ACS Appl Material Inter, J Adv Ceramic, J Euro Ceramic Soc, and J Am Ceramic Soc, and obtained more than 20 patents. He served as the deputy editor in chief of the International Journal of Applied Ceramic Technology, and the editorial board member of Coating.

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508

About SciOpen 

SciOpen is an open access resource of scientific and technical content published by Tsinghua University Press and its publishing partners. SciOpen provides end-to-end services across manuscript submission, peer review, content hosting, analytics, identity management, and expert advice to ensure each journal’s development. By digitalizing the publishing process, SciOpen widens the reach, deepens the impact, and accelerates the exchange of ideas.