In-situ formation of borides and their effect on structure and mechanical properties of AlNiCrTiB high-entropy alloy prepared by electron-beam sintering

DOI: 10.62564/M4-SN1943

Serhii Nakonechnyi, Alexandra Yurkova, Petro Loboda

National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute»


Metal-ceramic composites based on high-entropy alloys have an excellent combination of various properties of metal and ceramic materials [1]. At the same time, one of the most promising ways to obtain such composites is the introduction of non-metallic elements, such as boron [2, 3]. The in-situ formation of ceramic particles/fibers can significantly improve different characteristics of the resulting composite. In this study, a mechanically alloyed, for 10 h in petrol environment, equiatomic powder mixture of the Al-Ni-Cr-Ti-B system was sintered by electron beam method using different currents (4, 6 and 8 mA) applied to the cathode of electron beam gun. At the current strength of 4 mA, an alloy exhibits the transformation of the BCC phase resulted from MA into the FCC phase, as well as the formation of small inclusions of boride phases based on Cr and Ti. An increased average microhardness of 7.5 GPa is achieved due to interstitial strengthening by dissolution of boron element in the voids of solid-solution lattice and alloy quenching. Increasing the current strength to 6 mA leads to the formation of a significant amount of titanium diboride inclusions. However, a higher content of the BCC phase is transformed into a soft FCC phase, reducing the average microhardness to 3.0 GPa. At a current of 8 mA, the phase composition of the alloy does not change, but three heating zones are formed in the microstructure. In the zone of electron beam contact, a FCC matrix with inclusions of chromium monoboride fibers is formed, and the average microhardness here is 7.4 GPa. Inside the sample, at a distance of 2-3 mm, the microstructure consists of a same FCC matrix and titanium diboride inclusions, and the average microhardness reaches 11.8 GPa. After that, the microstructure and microhardness of the alloy are like those obtained at 6 mA. The results reflect the prospects and the necessity of further research on the formation of the structure and properties of such materials.

Keywords
High entropy alloys; Electron-beam sintering; Borides; Structure; Mechanical properties.

Acknowledgments
This study was funded under the project of the Ministry of Education and Science of Ukraine, state registration number 0124U000913.

References
[1] M.A. Mehmood, K. Shehzad, M. Mujahid, T.B. Yaqub, A. Godfrey, F. Fernandes, F.Z. Muhammad, K. Yaqoob, Ceramic-reinforced HEA matrix composites exhibiting an excellent combination of mechanical properties, Sci. Rep., 2022. V. 12. Article Number 21486. [2] B. Xin, A. Zhang, J. Han, J. Zhang, J. Meng, Enhancing mechanical properties of the boron doped Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloy via tuning composition and microstructure, J. Alloys Compd., 2022. V. 896. Article Number 162852. [3] J. Chen, Y. Long, H.-T. Lin, F. Zhang, Friction and wear behaviors of boron-containing high entropy alloy/diamond composites, Diam. Relat. Mater., 2024. V. 144. Article Number 110998.