Grain boundaries(GBs)are often known as intergranular cracking sources in alloys at high temperatures,resulting in limited high-temperature strength and ductility.Here,we propose a GB-dual-carbide(de-noted as GB-DC)st...Grain boundaries(GBs)are often known as intergranular cracking sources in alloys at high temperatures,resulting in limited high-temperature strength and ductility.Here,we propose a GB-dual-carbide(de-noted as GB-DC)strengthening strategy and have developed a high-performance(NiCoFeCr)_(99)Nb0.5 C_(0.5) high-entropy alloy(HEA)with exceptional strength-ductility synergy at 1073 K.Chain-like coherent M23 C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic(FCC)matrix during deformation.Nano-scale NbC particles are distributed alternatively between M_(23)C_(6) carbides and inhibit their coarsening.Both strength and duc-tility of the GB-DC HEA increase dramatically at strain rates ranging from 10^(−4) to 10^(−2) s^(−1) at 1073 K,compared with those of the single-phase NiCoFeCr HEA.Specifically,yield strength of 142 MPa,ultimate tensile strength of 283 MPa,and elongation of 34%were obtained,which are twice that of the refer-ence NiCoFeCr HEA(82 MPa,172 MPa,and 18%,respectively).EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature,and TEM analysis revealed that dislo-cations can go through the coherent phase boundaries(CPBs)and activate dipoles inner M_(23)C_(6) carbides,which weakened the stress concentration in GBs.This substantially reduces the critical stress for dislo-cation generation and transmission to a stress level lower than that required for intergranular fracture.Theoretical estimation suggests that carbides result in a much higher activation energy(∼510 kJ/mol)for GB sliding and a rather low interface energy(∼101 mJ/m^(2))compared with the GB energy(1000 mJ/m^(2)),which rationalizes the enhanced GB cohesion by carbides.展开更多
基金sponsored by the fund of National Natural Sci-ence Foundation of China(Grant No.52371028 and 52271097)the State Key Laboratory of Solidification Processing in NPU(Grant No.SKLSP202401)the Fundamental Research Funds for the Central Universities,HUST(No.2023JYCXJJ016).
文摘Grain boundaries(GBs)are often known as intergranular cracking sources in alloys at high temperatures,resulting in limited high-temperature strength and ductility.Here,we propose a GB-dual-carbide(de-noted as GB-DC)strengthening strategy and have developed a high-performance(NiCoFeCr)_(99)Nb0.5 C_(0.5) high-entropy alloy(HEA)with exceptional strength-ductility synergy at 1073 K.Chain-like coherent M23 C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic(FCC)matrix during deformation.Nano-scale NbC particles are distributed alternatively between M_(23)C_(6) carbides and inhibit their coarsening.Both strength and duc-tility of the GB-DC HEA increase dramatically at strain rates ranging from 10^(−4) to 10^(−2) s^(−1) at 1073 K,compared with those of the single-phase NiCoFeCr HEA.Specifically,yield strength of 142 MPa,ultimate tensile strength of 283 MPa,and elongation of 34%were obtained,which are twice that of the refer-ence NiCoFeCr HEA(82 MPa,172 MPa,and 18%,respectively).EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature,and TEM analysis revealed that dislo-cations can go through the coherent phase boundaries(CPBs)and activate dipoles inner M_(23)C_(6) carbides,which weakened the stress concentration in GBs.This substantially reduces the critical stress for dislo-cation generation and transmission to a stress level lower than that required for intergranular fracture.Theoretical estimation suggests that carbides result in a much higher activation energy(∼510 kJ/mol)for GB sliding and a rather low interface energy(∼101 mJ/m^(2))compared with the GB energy(1000 mJ/m^(2)),which rationalizes the enhanced GB cohesion by carbides.
