Microstructural evolution in a precipitate-hardened (Fe0.3Ni0.3Mn0.3Cr0.1)94Ti2Al4 multi-principal element alloy during high-pressure torsion.

Multi-principal element alloys demonstrate high strength, thermal stability, and irradiation resistance, making them excellent candidate materials for applications in nuclear reactors and other harsh environments. Some studies have examined the use of high-pressure torsion to strengthen MPEAs through grain size reduction and strain hardening. However, no studies have investigated the effect of HPT on secondary phases (precipitates) within an MPEA. Two alloys, (Fe0.3Ni0.3Mn0.3Cr0.1)94Ti2Al4 containing Ni(Ti, Al) B2 phase, and CrFe σ phase, and single-phase Fe0.3Ni0.3Mn0.3Cr0.1, were fabricated by casting and heat treatment. Both alloys were then processed with HPT to study microstructural evolution. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the alloys before and after HPT processing. HPT processing produced a nanocrystalline structure in both alloys, but (Fe0.3Ni0.3Mn0.3Cr0.1)94Ti2Al4 exhibited a significantly smaller grain size and higher dislocation density than Fe0.3Ni0.3Mn0.3Cr0.1, with corresponding higher hardness. Before HPT, the (Fe0.3Ni0.3Mn0.3Cr0.1)94Ti2Al4 alloy consisted of large grain (~ 400 μm) and precipitates, including B2 of ~ 38 μm average size, B2 of ~ 0.7 μm average size, and small amounts of σ of ~ 1.5 µm average size. After HPT, the larger B2 precipitates were decreased in size and volume fraction, while the smaller B2 precipitates were completely dissolved; the σ precipitates appeared unaffected by HPT, likely due to their much higher hardness. Observation of the B2 precipitate distribution along radial distance indicates that the strain caused the precipitates to fracture at intermediate strain (γ = 125) and dissolve at high strain (γ = 280). [ABSTRACT FROM AUTHOR]