Ultra-hard, multi-phase nanocrystalline MoTa and MoTaTi based concentrated refractory alloys

Binary (MoTa) and ternary (MoTaTi) based concentrated refractory alloys are synthesized using ball milling and spark plasma sintering. A single BCC phase which was observed after high energy ball milling has transformed to multiple phases after sintering. Presence of Ti and Fe (from milling media) appears to trigger the phase transformations. An extremely high hardness in the range 16-10 GPa was measured in the load range 0.25-9.81 N and with a very distinct indentation size effect. Density-normalized hardness was found to be exceptionally high indicating their potential for high strength/density applications. This study also suggests that several elements need not be added in high concentrations to achieve high end mechanical properties.

Automated summary

Binary and ternary based concentrated refractory alloys were synthesized and studied, and it was found that the BCC phase transformed into multiple phases after sintering, possibly triggered by the presence of Ti and Fe. The alloys exhibited extremely high hardness in a specific load range, with a distinct indentation size effect. Additionally, the study revealed that high end mechanical properties can be achieved without the addition of a large number of elements.