**4. Discussion**

Compared to the conventional assays, the high-throughput assays employed in this work required significantly smaller material volumes. It should be noted that a total of 15 material conditions (obtained by combining three different post-build aging heat treatments with five different compositions) were produced and studied with relatively low overall effort and cost. In fact, the high-throughput (HT) assays described in this work exhibit tremendous potential for further scale-up, allowing the rapid evaluation of several hundreds of material conditions. In addition to requiring only small volumes of the material, the time and effort needed for the proposed HT assays are also significantly lower compared to those for the conventional assays. This is because the sample preparation steps only require standard metallography protocols that are needed anyway if the material microstructure is to be documented in such explorations.

As demonstrated in previous studies [37,39,82,105], the averaged values from the multiple indentations summarized in Figure 7 provide reliable measures of the bulk properties measured in standardized tests. The estimated Young's moduli did not show clearly identified trends between the different material conditions explored in this study, and fell in the range of 97–130 GPa. In general, one might expect a decrease in the Young's modulus with an increase in the β volume fraction, as the β phase is expected to exhibit a lower elastic modulus compared to the α phase [106,107]. Although one might be tempted to infer such a trend from Figure 7, it is not clearly evident, as the noise in the measurements is of the same order as the overall variation among the tested samples. However, the overall range of the values estimated in this work is comparable to the ranges published in the literature [108,109] for similar compositions.

As seen in Figure 7, the indentation yield strengths and the indentation hardening rates in the early stages of the imposed plastic deformation increased systematically with the increase in Mn content. There is, as expected, a clear positive correlation between the indentation yield strength, the indentation hardening rates and the Mn content. Strengthening due to secondary phase, solid solution strengthening, and grain boundary strengthening are likely to contribute to the observed increase in the indentation strength with the increase in Mn content. Based on prior work [110], the indentation yield strengths can be converted to tensile yield strengths using a scaling factor of 2.0. Using this scaling factor, the tensile yield strengths for the material conditions studied are expected to range between 828 and 1864 MPa, which is among the highest ranges reported [108,111–113] for similar compositions. Interestingly, the highest values were obtained for the samples with the highest Mn content and the lowest post-build aging treatment. Indeed, the corresponding microstructures also showed a relatively high β volume fraction of about 65% and highly refined microstructures with averaged CLs of 0.17 and 0.32 µm in the α and β phases, respectively (see Figure 5). The refined length scales are also responsible for the high indentation hardening rates measured in our experiments, because of the presence of a much larger number of interfaces per unit volume of the material. The fact that our high-throughput protocols easily identified the viability of obtaining a very high yield strength in the Ti–Mn alloys along with the features identified in their microstructures clearly testifies to the unique benefits of our approach for the rapid exploration of large material spaces.
