FATIGUE-CRACK GROWTH-RATES AND FRACTURE-TOUGHNESS OF RAPIDLY SOLIDIFIED AL-8.5 PCT FE-1.2 PCT V-1.7 PCT SI ALLOYS

The room-temperature fatigue crack growth rates (FCGR) and fracture to ughness 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 pro duced by the PFC process, properties were determined in six different orientations, including the short transverse directions S-T and S-L. D iffusion bonding and adhesive bonding methods were used to prepare spe cimens for determining FCGR and fracture toughness in the short transv erse direction. Interparticle boundaries control fracture properties i n the alloy produced by PFC. Fracture toughness of the PFC alloy varie s from 13.4 MPa square-root m to 30.8 MPa square-root m, depending on the orientation of the crack plane relative to the interparticle bound aries. Fatigue crack growth resistance and fracture toughness are grea ter 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-depo sited condition or in the extruded condition. The fracture toughness v aries from 17.2 MPa square-root m to 18.5 MPa square-root m for die as -deposited condition and from 19.8 MPa square-root m to 21.0 MPa squar e-root m for the extruded condition. Fracture properties are controlle d by intrinsic factors in the alloy produced by AMD. Fatigue crack gro wth 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 opti cal metallographic examination of crack-microstructure interactions an d scanning electron microscopy of the fracture surfaces.