Deformation and fracture behavior of laser processed dense and porous Ti6Al4V alloy under static and dynamic loading

Abstract

Deformation and fracture behavior of laser processed dense and porous Ti6Al4V alloy under uniaxial static and dynamic compression loadings were experimentally investigated in this study. Samples with 0, 10 and 20 porosities were fabricated using a continuous wave Nd-YAG laser in a controlled environment. The dynamic tests were performed at the strain rates of 1�10 3, 4�10 3 and 8�10 3/s using the split Hopkinson pressure bar (SHPB) test system and the static tests were done at the strain rate of 1�10 -3/s. In addition, SEM and EBSD analyses were also carried out to study the failure mechanisms and texture development due to solidification and deformation. Both deformation and fracture exhibited appreciable rate sensitivity. For the former, the material strength increased, and for the latter, the failure strains decreased with the increased strain rates. The 20 porous Ti6Al4V showed lower strength, but higher ductility compared to the 10 material, but the 10 porous material had both less strength and ductility than the dense (0 porosity) material and the ductility of 20 porous material was only comparable to that of the dense material, i.e., did not exhibit appreciable increase of ductility. The texture analysis indicated that all the samples had reasonably consistent textures due to solidification. Hence the texture effect is essentially negligible and the observed material behavior is mainly a manifestation of the induced porosity. Both the macroscopic experiments and the microstructure analysis suggest that the formation of adiabatic shear band (ASB) could likely be the major failure mechanism for Ti6Al4V and the pores likely be the sites for nucleating ASB and subsequent catastrophic failure. For initially dense Ti6Al4V, the failure and the corresponding failure strain seem to depend on the duration of the incubation period for developing a nucleation site. © 2012 Elsevier B.V