The behavior of materials in extreme environment is one of the problems which restricts the application and development of nuclear energy, for materials determine the feasibility, safety and economy of the nuclear energy system. The innovations of nuclear power technology have significantly improved the utilization rate and safety of nuclear energy. However, the stricter working conditions put higher demands on materials. 

By using various methods, researchers are attempting to avoid or overcome the shortcomings of traditional steel and ceramic materials, such as poor high-temperature mechanical properties and brittle properties.  

A class of compounds material, which is called M_n+1AX_n (MAX phase), has attracted much attention as it shows good properties of both metal and ceramic materials. Because of its unique non-van der Waals-type layered structure, it features high-temperature resistance, oxidation resistance, high strength, high toughness, high thermal conductivity and irradiation resistance, etc. Therefore, it is a potential candidate for structural materials, protective coating or heterogeneity welding materials in advanced nuclear energy systems. 

Relying on irradiation research devices such as the Heavy Ion Research Facility in Lanzhou (HIRFL), Low Energy Highly-Charged Ion Accelerator Facility (LEAF), and 320 kV Highly Charged Ion Beam Platform for Multidiscipline Researches (320 kV), researchers from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) have made important progress in a series of systematic studies on 312-MAX phase materials, including the irradiation performance evaluation, the mechanism of irradiation resistance, irradiation-induced phase transformation and its evolution.  

For the first time, the researchers have systematically investigated and confirmed the phase transformation from α to β to γ and finally to fcc phase in 312-MAX phase material irradiated at room temperature.  

They also found the invert process of recovery in samples irradiated at high temperatures. Then they demonstrated and clarified the ways and mechanisms of irradiation induced phase transformation (lattice atom recombination) by different experiments, confirming that the lattice dissipation and the saturation of vacancy-type defects are the main reasons for the amorphization resistance.  

Moreover, the researchers also clarified the puzzle of β-phase microstructure and presented the correct method of expression and related properties.  

These results are of great significance to the research of nuclear materials, especially to the design of irradiation-resistant materials and the deep understanding of the evolution of irradiation damage. 

Related results have been published in Acta Materialia and Journal of Applied Physics.  

This work was financially supported by the National Natural Science Foundation of China and the Youth Innovation Promotion Association of CAS. 

Fig. 1 Schematic diagram of Ti₃AlC₂ series of phase transformations induced by irradiation, each of phase components, and their structures from TEM images. (Image by SUN Jianrong)