SUMMARY

Recent work has shown the capability of spherical nanoindentation to capture local structure-property relationships in polycrystalline cubic metals by measuring indentation stiffness and yield strength from stress-strain curves as a function of the local microstructure in the indentation zone. However, these protocols capture structure-property relationships at only one level of the material hierarchy (e.g., single grains). Thus it is still very difficult to infer bulk structure-property relationships using these indentation protocols, which is mainly due to a lack of understanding indentation length scale effects and the important role played by structural hierarchy (i.e., unique structural features at different length scales). It is the goal of this work to extend these protocols to systematically study length scale effects of mechanical properties (e.g., indentation stiffness and yield strength) in titanium alloys. Alpha-beta titanium alloys were chosen because they display a rich variety of two phase microstructures and structural hierarchy and are well documented in literature. Firstly, nanoindentation protocols are extended to characterize the elastic and plastic anisotropy of a hexagonally close packed metal (alpha titanium in commercially pure and alloy Ti-6Al-4V) and a two phase microstructure (alpha-beta colony in Ti-6Al-4V). Secondly, spherical microindentation stress-strain protocols are developed and employed to characterize polycrystalline volumes in three titanium alloys (commercially pure, Ti-6Al-4V, and Ti18). The results of these major advances in indentation protocols and systematic study of length scale effects on the mechanical properties in Ti-6Al-4V will be presented and discussed along with applications demonstrating their high throughput nature to rapidly explore alloy development.