A FeCoCrNiMo 2.3 high entropy alloy was processed by powder metallurgy with two conditions: hot extruded and annealed. In situ neutron Diffraction, together with electron microscopy, was used to study the deformation mechanisms and concomitant microstructural evolution for both conditions. The as-extruded alloy has a single face-centered-cubic structure with a calculated stacking fault energy of ~19 mJ/m 2. When the alloy is tensile deformed, nano-twins and microbands are induced, resulting in an excellent combination of strength and ductility. Annealing at 800 °C for 72 h led to an increase of the strength of the alloy, but a decrease of the ductility. This is due to the decomposition of the alloy after annealing, causing the formation of Mo-rich intermetallic particles and a decrease of the stacking fault probability. These results highlight that combined mechanisms (i.e. solute strengthening and twin/microband induced plasticity) can effectively improve both the strength and ductility of high entropy alloys. [1]. One typical HEA system is based on five transition elements (Ni, Cr, Mn, Fe and Co), denoted here as tHEA, e.g. FeCoCrNiMn [1]. This system has been developed extensively with a number of variants in compositions, showing great potential for creating exceptional engineering alloys [2-9]. Although many of tHEA variants form multi-phase microstructures with superior properties [6,10-12], single phase FeNiCrMnCo based tHEAs are still desirable in order to make use of high entropy effects, and to illustrate fundamental mechanical aspects of HEAs. Single phase tHEA can be obtained by thermo-mechanical processing of cast alloys [10] or powder metallurgy (PM) approaches [4,13,14]. Here, we have produced a face-centered cubic (FCC) single phase FeCoCrNiMo 0.23 alloy (tHEA-Mo) through a powder metallurgy route. This powder metallurgy process includes (i) fabrication of pre-alloyed tHEA-Mo powder via gas atomization, and (ii) hot extrusion of the canned powders, as detailed in Ref. [14]. The newly-developed FeNiCrCoMo 0.23 alloy displays an excellent strength-ductility combination (see Table 1) with an ultimate tensile strength of 784 MPa and elongation over 50%. A good combination of strength and ductility has been found in various tHEA variants, which is attributed to twinning induced plasticity (TWIP) [2,7,10,15], phase transformation induced plasticity [16] and/or micro-band formation [17]. Interestingly, all three mechanisms have also been identified in austenite steels with a low to medium stacking fault energy [18-20]. By analogy with its counterparts and austenite steels, we suspect that similar mechanisms may play an important role in the outstanding strength and ductility of the present tHEA-Mo alloy, which we aim to confirm in this study. Transmission electron microscopy (TEM) has generally been used to study the microstructural response to the applied deformation in a wide variety of tHEAs, revealing the dislocation structure formation [17], stacking faults [21], deformation twins [2], and microband...
Investigating nano-precipitation in a V-containing {HSLA} steel using small angle neutron scattering. Acta Materialia
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