Design of a cast Al-based Al-Ni-Cr-Zr eutectic alloy with excellent high temperature mechanical properties

Abstract

The present work reports the design of a cast ternary Al-3.8Ni-0.5Cr eutectic alloy for high-temperature applications with a minor Zr addition (0.15 at %). In the peak-aged condition (375 °C for 20 h), the alloy exhibited a hardness of 120 ± 3 HV and yield strengths of 355 ± 15, 225 ± 10, and 197 ± 8 MPa at 25, 200, and 250 °C, respectively. Notably, the alloy maintained a yield strength of 335 ± 25 MPa after long-term heat treatment at 375 °C for 100 h. The excellent microstructural stability and high-temperature strength are attributed to the presence of coherent and stable L1₂-ordered precipitates within the soft α-Al matrix of the eutectic phase. TEM weak-beam imaging revealed precipitate shearing via a planar dislocation glide mechanism, suggesting glide plane softening at 25 °C. Theoretical calculations predicted optimal strengthening from ordering, with peak strength achieved for precipitate sizes of ∼2.4 nm.