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

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 degrees 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 degrees C, respectively. Notably, the alloy maintained a yield strength of 335 +/- 25 MPa after long-term heat treatment at 375 degrees C for 100 h. The excellent microstructural stability and high-temperature strength are attributed to the presence of coherent and stable L1(2)-ordered precipitates within the soft alpha-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 degrees C. Theoretical calculations predicted optimal strengthening from ordering, with peak strength achieved for precipitate sizes of similar to 2.4 nm.