An oxide-dispersion-strengthened(ODS)Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy with a bimodal grain size distribution was developed via a simple process of internal oxidation and powder forging.The intentionally promoted heterog...An oxide-dispersion-strengthened(ODS)Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy with a bimodal grain size distribution was developed via a simple process of internal oxidation and powder forging.The intentionally promoted heterogeneous microstructure consists of coarse-grained“core”regions enclosed by mutually connected fine-grained“shell”zones,facilitated by unevenly distributed oxide particles.The sample sintered and then forged at 1150℃exhibited a yield strength of 598 MPa,a tensile strength of 734 MPa,and a fracture elongation of 25.1%.Such simultaneously enhanced strength and ductility are significantly above those of cast or previous powder-consolidated counterparts.During tensile deformation,a strain gradient is built up across the inhomogeneous grains and a high density of geometrically necessary dis-locations was observed near the interfaces of matrix/oxide particles,both contributing to heterogeneous deformation-induced strengthening.This elevates the work hardening rate and consequently the tensile elongation.Quantitative analysis indicates that the dislocation build-up during forging makes the dom-inant contribution to the high yield strength of Ox-1150.The present study offers a new route to the preparation of heterogeneously structured ODS Fe-Cr-Al alloys and provides guidance for optimizing the mechanical properties of such alloys in terms of strength-ductility synergy.展开更多
As one of the most effective mechanisms,precipitation-hardening is widely used to strengthen high-entropy alloys.Yet,heavy precipitation-hardened high-entropy alloys usually exhibit serious embrittlement.How to effect...As one of the most effective mechanisms,precipitation-hardening is widely used to strengthen high-entropy alloys.Yet,heavy precipitation-hardened high-entropy alloys usually exhibit serious embrittlement.How to effectively achieve ultra-high strength and maintain reliable ductility remains a challenge.Here,we report a study of doping extremely little boron to meet this target.We found that adding of 30 ppm boron into the heavy Ti and Al alloyed FCC FeCoNiCr high-entropy,(FeCoNiCr)_(88) Ti_(6) Al_(6) HEA(at.%)which is strengthened mainly by both coarse BCC-based(Ni,Co)_(2) TiAl Heusler and fine L12-type FCC-based(Ni,Co)_(3) TiAl precipitates and shows ultrahigh strength but poor ductility,could significantly change the original microstructure and consequently improve mechanical performance,owing to the well-known effect of boron on reducing the energy of grain boundaries.The boron addition can(1)eliminate microcavities formed at Heusler precipitate-matrix interfaces;(2)suppress the formation and segregation of coarse BCC Heusler precipitates;(3)promote the formation of L12 nanoparticles.This changes of microstructure substantially improve the tensile ductility more than by~86%and retain comparable or even better ultimate tensile strength.These findings may provide a simple and costless solution to produce heavy precipitation-strengthened HEAs with ultrahigh strength and prevent accidental brittleness.展开更多
基金supported by the Innovative Scientific Program of CNNC(No.J202107006-02).
文摘An oxide-dispersion-strengthened(ODS)Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy with a bimodal grain size distribution was developed via a simple process of internal oxidation and powder forging.The intentionally promoted heterogeneous microstructure consists of coarse-grained“core”regions enclosed by mutually connected fine-grained“shell”zones,facilitated by unevenly distributed oxide particles.The sample sintered and then forged at 1150℃exhibited a yield strength of 598 MPa,a tensile strength of 734 MPa,and a fracture elongation of 25.1%.Such simultaneously enhanced strength and ductility are significantly above those of cast or previous powder-consolidated counterparts.During tensile deformation,a strain gradient is built up across the inhomogeneous grains and a high density of geometrically necessary dis-locations was observed near the interfaces of matrix/oxide particles,both contributing to heterogeneous deformation-induced strengthening.This elevates the work hardening rate and consequently the tensile elongation.Quantitative analysis indicates that the dislocation build-up during forging makes the dom-inant contribution to the high yield strength of Ox-1150.The present study offers a new route to the preparation of heterogeneously structured ODS Fe-Cr-Al alloys and provides guidance for optimizing the mechanical properties of such alloys in terms of strength-ductility synergy.
基金the National Natural Science Foundation of China(NSFC)under Grant Nos.51871178。
文摘As one of the most effective mechanisms,precipitation-hardening is widely used to strengthen high-entropy alloys.Yet,heavy precipitation-hardened high-entropy alloys usually exhibit serious embrittlement.How to effectively achieve ultra-high strength and maintain reliable ductility remains a challenge.Here,we report a study of doping extremely little boron to meet this target.We found that adding of 30 ppm boron into the heavy Ti and Al alloyed FCC FeCoNiCr high-entropy,(FeCoNiCr)_(88) Ti_(6) Al_(6) HEA(at.%)which is strengthened mainly by both coarse BCC-based(Ni,Co)_(2) TiAl Heusler and fine L12-type FCC-based(Ni,Co)_(3) TiAl precipitates and shows ultrahigh strength but poor ductility,could significantly change the original microstructure and consequently improve mechanical performance,owing to the well-known effect of boron on reducing the energy of grain boundaries.The boron addition can(1)eliminate microcavities formed at Heusler precipitate-matrix interfaces;(2)suppress the formation and segregation of coarse BCC Heusler precipitates;(3)promote the formation of L12 nanoparticles.This changes of microstructure substantially improve the tensile ductility more than by~86%and retain comparable or even better ultimate tensile strength.These findings may provide a simple and costless solution to produce heavy precipitation-strengthened HEAs with ultrahigh strength and prevent accidental brittleness.
