Improved elevated-temperature strength and thermal stability of additive manufactured Al–Ni–Sc–Zr alloys reinforced by cellular structures

Abstract

Laser powder bed fusion (LPBF) processed Al–Ni alloys typically exhibit cellular structures, contributing to superior strength at ambient temperature as the cell walls can effectively impede dislocation motion during plastic deformation. However, it is still unclear whether cellular structures can lead to excellent elevated-temperature performance. In this study, we conducted a systematic investigation into the elevated-temperature mechanical properties and thermal stability of an LPBF Al–Ni–Sc–Zr alloy with cellular structures. The as-built alloy exhibits a yield strength of 368 MPa at 25℃ and 332 MPa at 250℃, with an exceptional strength retention rate of ∼90 % at 250℃. Moreover, the alloy maintains a hardness of ∼146 HV following exposure at 250℃ for 100 h and shows no apparent decrease despite increasing the exposure time to 500 h. The excellent elevated-temperature performance can be attributed to the cellular structures. The cell walls effectively confine dislocations at elevated temperatures, suppressing the dislocation annihilation and leading to exceptional strength retention. On the other hand, even if the cell walls decompose into nanoparticles after prolonged thermal exposure, the reduction in strength due to the decomposition can be compensated by the strengthening of the nanoparticles, resulting in excellent thermal stability. By studying the influence of the cellular structures on elevated-temperature performance, this study could provide valuable insights into developing high-performance Al alloys for elevated-temperature applications by additive manufacturing.