Effect of withdrawal rate on the microstructure and room temperature mechanical properties of directionally solidified NiAl–Cr(Mo)–(Hf, Dy)–4Fe alloy

Abstract

The microstructures and room temperature mechanical properties of directionally solidified NiAl–Cr(Mo)–(Hf, Dy)–4Fe alloy at different withdrawal rates were investigated using SEM, EDS, TEM, three-point bending tests and compressive tests. When the withdrawal rate changes from 6 μm/s to 240 μm/s, the solid–liquid interface undergoes the transition of planar→cellular→dendritic morphology. With increasing the withdrawal rate, the interlamellar spacing decreases by degree, and the lamellar structures at the center of eutectic dendrite are well-aligned and parallel to the growth direction, thus resulting in the improvement of fracture toughness and compressive yield strength at a moderate withdrawal rate (60 μm/s). Moreover, the observation of side surface and fracture surface can roughly reveal the changed trend of fracture toughness and compressive yield strength by identifying the zigzag and coarse degree of fracture surface or the specific morphology features. The toughening and strengthening mechanisms are also discussed.