Microtensile characterization of titanium 5111 alloy mechanical properties and comparison of failure mechanisms at two microstructural length scales

Abstract

Micro-scale mechanical characterization of materials is a useful technique for understanding local material behavior, particularly where inhomogeneous materials or microstructures are present. In this work, a custom microsample testing system that utilizes digital image correlation (DIC) is used to measure the response of samples that have a 3 mm × 1 mm footprint and a cross sectional gage area of 250 μm × 250 μm. The mechanical behaviors of Ti-5111 base metal and friction stir weld refined microstructures were examined. In a novel use of strain contour mapping, microstructural analysis and measurements were performed directly on microsamples and these results were linked to the fractography and measured properties using the DIC data. Larger variations, in several mechanical properties, were measured in the base metal Ti-5111 than in the weld material. For example, the yield base metal stress was 771 ± 41 MPa versus 828 ± 9 MPa for the weld. These variations were found to be due to the larger colony structure of the wrought plate. The colonies in wrought plate Ti-5111 can be as large as 250 μm and were found to promote the formation of shear bands which resulted in reduced ductility.