Fatigue Crack Growth and Fracture Toughness in Bimodal Al 5083

摘要

The fatigue crack growth rates and fracture toughness of bulk nanocrystalline Al 5083 having a bimodal grain size distribution were investigated. The nanocrystalline powders were prepared by mechanically ball milling spray atomized Al 5083 powders in liquid nitrogen. This nanocrystalline powder was blended with 50 wt% spray atomized large grained Al 5083 powders. The blended powder was then cold pressed, degassed, and extruded into rods. The bimodal Al 5083 thus produced consists of nanocrystalline grain bands and coarse grain bands. While the yield strength of the bimodal Al 5083 is about 25% lower than that of the all nanocrystalline Al 5083, its tensile ductility is almost 50% greater. In addition, the fracture toughness of the bimodal material is about 85% higher than that of the all nanocrystalline counterpart. Fatigue crack growth rates of bimodal Al 5083 are about 30% lower than those of all nanocrystalline Al 5083. The lower fatigue crack growth rates are accompanied by more tortuous crack paths when the crack propagated through the coarse grain regions in the bimodal Al 5083.