An investigation of the effects of loading rate on resistance-curve behavior and toughening in cast lamellar gamma-based titanium aluminides

This article presents the results of a combined experimental and theoretica l study of the effects of loading rate (1, 10, and 100 MPa rootm . s(-1)) o n the resistance-curve behavior and toughening in cast lamellar gamma-based titanium aluminides (Ti-48Al-2Cr-2Nb, Ti-45Al-2Mn-2Nb + 0.8 vol pct TiB2, and Ti-47Al-2Mn-2Nb + 0.8 vol pct TiB2). Note that compositions are quoted in at. pet unless stated otherwise. The fracture-initiation toughness and r esistance-curve behavior in Ti-48Al-2Cr-2Nb are shown to be similar at the three loading rates examined. In the case of the Mn-containing alloys, stro nger resistance-curve behavior is observed as the loading rate increases fr om 1 to 10 MPa rootm . s(-1). However, the fracture-initiation toughness an d resistance-curve behavior of the Mn-containing alloys are similar at load ing rates of 10 and 100 MPa rootm . s(-1). The observed resistance-curve be havior is attributed largely to the role of ligament bridging and, to a les ser extent, to the effects of crack-tip plasticity. Small- and large-scale bridging models are also shown to predict the measured resistance curves wh en the observed/measured bridging parameters and material properties are us ed in the micromechanical modeling of crack bridging. The implications of t he results are also discussed for the design of damage-tolerant gamma alloy s and microstructures.