Zhiqiang Fu

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

HEAs’ compositional space allows the design of hierarchical microstructures that contribute to the exceptional strength values. High-entropy alloys (HEAs) are a class of metallic materials that have revolutionized alloy design. They are known for their high compressive strengths, often greater than 1 GPa; however, the tensile strengths of most reported HEAs are limited. Here, we report a strategy for the design and fabrication of HEAs that can achieve ultrahigh tensile strengths. The proposed strategy involves the introduction of a high density of hierarchical intragranular nanoprecipitates. To establish the validity of this strategy, we designed and fabricated a bulk Fe25Co25Ni25Al10Ti15 HEA to consist of a principal face-centered cubic (fcc) phase containing hierarchical intragranular nanoprecipitates. Our results show that precipitation strengthening, as one of the main strengthening mechanisms, contributes to a tensile yield strength (σ0.2) of ~1.86 GPa and an ultimate tensile strength of ~2.52 GPa at room temperature, which heretofore represents the highest strength reported for an HEA with an appreciable failure strain of ~5.2%.

Influence of Cr removal on the microstructure and mechanical behaviour of a high-entropy Al0.8Ti0.2CoNiFeCr alloy fabricated by powder metallurgy

ABSTRACT We report a systematic study on the influence of Cr removal on the microstructure and mechanical behaviour of an ultra-fine grained (UFG) high-entropy alloy (HEA), Al0.8Ti0.2CoNiFeCr, fabricated via spark plasma sintering (SPS) of mechanically alloyed (MA’ed) powders from constituent elemental powders. The MA’ed Al0.8Ti0.2CoNiFeCr powders consist principally of a BCC phase (∼85 vol.-%) with a small amount of FCC phase (∼15 vol.-%), whereas the MA’ed Al0.8Ti0.2CoNiFe powders present similar phases to those in the MA’ed Al0.8Ti0.2CoNiFeCr powders. Interestingly, the SPS processed UFG Al0.8Ti0.2CoNiFeCr alloy contains mostly an FCC phase (∼78 vol.-%) and some BCC phase (∼22 vol.-%); in contrast, the SPS processed UFG Al0.8Ti0.2CoNiFe alloy consists of a slightly enriched BCC phase (∼53 vol.-%) and an FCC phase (∼47 vol.-%). In addition, the SPS processed Al0.8Ti0.2CoNiFe alloy exhibits slightly higher yield strength, compressive strength and hardness but lower plasticity than those of the SPS processed Al0.8Ti0.2CoNiFeCr alloy. Special theme block on high entropy alloys, guest edited by Paula Alvaredo Olmos, Universidad Carlos III de Madrid, Spain, and Sheng Guo, Chalmers University, Gothenburg, Sweden.

Engineering heterostructured grains to enhance strength in a single-phase high-entropy alloy with maintained ductility

ABSTRACT Coarse-grained (CG) single-phase face-centered cubic (fcc) high-entropy alloys (HEAs) normally show insufficient room temperature strength. Here we design and implement a heterogeneous grain structure to strengthen a single-phase fcc Fe29Ni29Co28Cu7Ti7 HEA. Significantly, the heterostructured (HS) fcc HEA shows a dramatic enhancement (increasing from ∼350 to ∼614u2009MPa) in tensile yield strength as compared to its CG counterpart. As a result of its extraordinary work-hardening ability arising from the heterogeneous grain structure, the novel HS HEA exhibits a very high ultimate strength of ∼1308u2009MPa, and a good ductility of ∼23.1% which is almost identical to that of its CG counterpart. GRAPHICAL ABSTRACT IMPACT STATEMENT Introducing a heterogeneous grain structure to a soft fcc Fe29Ni29Co28Cu7Ti7 HEA, the heterostructured HEA shows significantly enhanced strengths at an essentially identical ductility as compared to the CG counterpart.