On the characteristic of ultrafine/nano precipitates and serration behavior in an Al-doped Fe3Cr2Ni multi-principle-element alloy

In this research, a class of Co-free Fe3Cr2NiAlx (x = 0–1.1) multi-principle-element alloys (MPEAs) with ultrafine/nano precipitates and serration behavior were fabricated. By varying Al element levels, the microstructure changed from a dual-phase structure of face-centered-cubic (FCC) plus body-centered-cubic (BCC) to a tri-phase structure of plate-like FCC, BCC and a uniformly dispersed nano-sized ordered B2 precipitates within BCC, then transformed to another dual-phase structure of BCC and the dual-morphology ultrafine/nano B2 precipitates within BCC. The increasing Al content resulted in a significant improvement in nanohardness (∼8.01 ± 0.32 GPa) and compressive yield strength (∼1284 ± 35 MPa) with keeping a large ductility (>60%), attributed to the uniform distribution of dual-morphology coherent B2 precipitates. The quantitative contributions of different strengthening mechanisms have been estimated in Fe3Cr2NiAl1.1 MPEA. A notable phenomenon has been discovered that Fe3Cr2NiAlx (x = 0.1–0.3) MPEAs showed the serration behavior near the yielding point of compressive stress-strain curves. In the compressive experiments with three different strain rates, as Al content increased, the serration type evolved from type B + C to type B. Serration behavior on stress-strain curves of alloys, impedes the engineering applications of alloys. It is critical to understand serration behavior of MPEAs in phenomenon and theory. This work has broader applicability to understand the effect of Al content on the microstructure and mechanical deformation behavior in MPEAs.