SPD Powder Route for HEA Alloy Production
Abstract
A comparative investigation of two fundamentally different approaches for the synthesis, microstructure evolution, and mechanical properties of the refractory-high-entropy alloys (RHEA) HfNbTaTiZr and HfNbTiZr was performed. The two methods comprised conventional arc (button) melting, and a powder route based on mechanical alloying and consolidation via severe plastic deformation (SPD). Powder consolidation via SPD involved different ranges of hydrostatic pressure, strain, and temperature. In particular, blended elemental (BE) powder was pre-compacted and subjected to one or four passes of equal channel angular pressing (ECAP) at 500 deg C and then ten revolutions of high-pressure torsion (HPT) at room temperature to an effective strain between 4 and 40. Some samples were then annealed at 500 deg C for one hour to investigate the thermal stability of the phases. The four ECAP passes at 500 deg C did not result in the formation of the BCC phase typical for the program RHEAs despite the presence of interfacial zones between particles and defect-driven diffusion. Nevertheless, a single ECAP pass was sufficient to create a solid bulk sample for subsequent HPT. After ten HPT revolutions, in contrast to melting route resulting in a single BCC phase alloy, both alloys formed new phases comprising on average 82 percent of a Nb-rich BCC phase and ~18 percent of a ZrHf-rich HCP phase in M1 alloy, and 85 percent a Nb-rich BCC phase and ~15 percent of a ZrHf-rich HCP phase in M2 alloy. After annealing treatment, the volume fraction of BCC phase decreased on average to 75 percent and volume fraction of HCP phase increased to ~25 percent in both alloys. Notably as result of annealing, the BCC phase in M2 alloy was transformed into two BCC phases with different cell parameters. That results in significantly increased hardness by 150-200 MPa.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 25, 2024
- Accession Number
- AD1230297
Entities
People
- Peter Hodgson
- Rimma Lapovok
Organizations
- Deakin University