The influence of strain rate and porosity on the deformation and fracture of titanium and nickel

The influence of strain rate on the tensile deformation and fracture behavior of powder-fabricated titanium and nickel containing porosity has been investigated. Measurements of uniform strain, local fracture strains, and elongations to failure show that, over the range of strain rates from 10-4 to 102 s-1, there is little or no effect of the strain rate on the fracture behavior of these materials at any of the porosity levels studied. In contrast, increasing porosity causes significant decreases in the yield stress, strain-hardening exponent, and ductility; these effects are more pronounced in the titanium than in the nickel. The porosity-induced loss of ductility can be understood in terms of the combined effects of enhanced geometric softening and shear localization due to a network of imperfections introduced into the materials by the presence of porosity. Secondary effects due to hydrogen embrittlement and thermal gradients forming during deformation are also noted