Strength of precipitates in Ni-Al and Ni-Al-Fe alloys

The present research combines Transmission Electron Microscopy and planar impact testing to investigate the geometry, concentration, and individual strengths of Ni3Al precipitates in Ni-Al and Ni-Al-Fe alloys. The study focuses on homogenized and aged samples of a binary (88.5% Ni, 11.5% Al) and a ternary (79.3% Ni, 10.2% Al, 10.5% Fe) systems. A detailed analysis of experimental results reveals significant difference between structures of the Ni3Al precipitates in these alloys. In the binary Ni-Al alloy, precipitates are predominantly small and dense spheres with an average diameter of 4 nm. Conversely, the ternary Ni-Al-Fe alloy exhibits larger and loose spherical precipitates, averaging 50 nm in diameter. A key finding of this study is the superior strength of smaller precipitates, which are approximately 40% stronger than their larger counterparts. The latter are identified as regions of Ni-based solid solution densely packed with minuscule, 2 nm-diameter, islands of the ordered Ni3Al phase. These insights contribute to a deeper understanding of the microstructural factors influencing the mechanical properties of Ni-Al based alloys.