The Effect of Microstructural Features and Thickness on Fracture Toughness of Ti–6Al–4V ELI Thin Sheets

Abstract

Thin plates made of Ti–6Al–4V ELI alloy are extremely useful and applicable material of implants industries. The present research is focused on the fracture toughness of Ti–6Al–4V ELI thin sheets through the mechanical and microstructural analyses. The load displacement curves resulted from tear testing methodologies in addition to tensile test were provided for both lamellar and equiaxed microstructures with three different thicknesses. Unit initiation and propagation energies, as an indication of fracture toughness, associated with tear strength were calculated from the curves. Furthermore, the influence of heat treatment’s soaking time for equiaxed microstructure and cooling rate for lamellar microstructure on tear testing, unit initiation and propagation energies was studied. In respect of the equiaxed microstructure, grain growth evolved from the extended soaking time was resulted in destructive effect on crack initiation resistance with increasing thickness, though it marginally affected the crack propagation resistance and fracture toughness. Regarding the lamellar microstructure, thinning the lamellas encouraged crack initiation and propagation resistance for thin sections. However, crack propagation resistance was reduced for thicker sections which contrasts with increasing crack initiation resistance by rising sample thickness. On overall view, increasing sample thickness associated with reducing the grain size was beneficial for crack resistance in equiaxed microstructure. In respect of the lamellar microstructures, thin lamellae particularly in thin sections was superior in terms of crack resistance.