Fatigue crack growth rates and fracture toughness of rapidly solidified Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloys

Abstract

The room-temperature fatigue crack growth rates (FCGR) and fracture toughness were evaluated for different crack plane orientations of an Al-8.5 Pct Fe-1.2 Pct V-1.7 Pct Si alloy produced by planar flow casting (PFC) and atomized melt deposition (AMD) processes. For the alloy produced by the PFC process, properties were determined in six different orientations, including the short transverse directions S-T and S-L. Diffusion bonding and adhesive bonding methods were used to prepare specimens for determining FCGR and fracture toughness in the short transverse direction. Interparticle boundaries control fracture properties in the alloy produced by PFC. Fracture toughness of the PFC alloy varies from 13.4 MPa√m to 30.8 MPa√m, depending on the orientation of the crack plane relative to the interparticle boundaries. Fatigue crack growth resistance and fracture toughness are greater in the L-T, L-S, and T-S directions than in the T-L, S-T, and S-L orientations. The alloy produced by AMD does not exhibit anisotropy in fracture toughness and fatigue crack growth resistance in the as-deposited condition or in the extruded condition. The fracture toughness varies from 17.2 MPa√m to 18.5 MPa√m for the as-deposited condition and from 19.8 MPa√m to 21.0 MPa√m for the extruded condition. Fracture properties are controlled by intrinsic factors in the alloy produced by AMD. Fatigue crack growth rates of the AMD alloy are comparable to those of the PFC alloy in the L-T orientation. The crack propagation modes were studied by optical metallographic examination of crack-microstructure interactions and scanning electron microscopy of the fracture surfaces.