Ductility Control via Nano-Precipitation at Grain Boundaries in Ti-Zr-Hf-Nb-Ta Multi-Principal Element Alloys

TL;DR

Adding Fe to Ti-Zr-Hf-Nb-Ta alloys creates strong but less ductile nano-precipitates, and adjusting Fe content and heat treatment can balance strength and ductility.

Contribution

A method to control nano-precipitation at grain boundaries to balance strength and ductility in multi-principal element alloys.

Findings

Aging at 500°C for 30 min reduced elongation from 17.5% to 7.5% due to Hf2Fe precipitates.

Adjusting Fe content and heat treatment achieved 1037 MPa strength with 14% elongation.

Ductility ranged from 2.65% to 19% while maintaining strength between 955 and 1081 MPa.

Abstract

The formation of nano-sized Hf2Fe precipitates at grain boundaries through Fe micro-alloying enhances the strength of Ti-Zr-Hf-Nb-Ta multi-principal element alloys (MPEAs), but this improvement comes at the cost of reduced ductility. Aging at 500 °C for just 30 min resulted in a marked reduction in elongation, from 17.5% to 7.5%. This decline is attributed to lattice mismatch between the precipitates and the matrix, as well as increased stacking stress at the grain boundaries. By adjusting the Fe composition and heat treatment parameters, the quantity of Hf2Fe at the grain boundaries of (TiZrHfNbTa)100−xFex alloy was effectively controlled, achieving a balanced combination of strength of 1037 MPa and elongation of 14%. Furthermore, this method enabled ductility modulation over a wide range, with elongation varying from 2.65% to 19% while maintaining alloy strength between 955 and 1081 MPa, providing valuable insights for tailoring these alloys to diverse application requirements. The precipitation thermodynamics of the (TiZrHfNbTa)100−xFex alloy was also investigated using the CALPHAD method, with thermodynamic calculations validated against experimental results, laying a foundation for more in-depth kinetic study of nano-size precipitates in these alloys. Additionally, the relationships between thermodynamics, precipitates evolution, and mechanical properties were discussed.

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