Refractory high-entropy alloys(RHEAs)stand as promising candidates for the development of a new generation of hightemperature materials due to their exceptional mechanical properties.However,the inherent low ductility...Refractory high-entropy alloys(RHEAs)stand as promising candidates for the development of a new generation of hightemperature materials due to their exceptional mechanical properties.However,the inherent low ductility and high density of RHEAs have hindered their widespread adoption in industrial applications.In this study,an Nb_(38)Ti_(35)Al_(15)V_(6)Cr_(4)(TaHfMoW)_(2) RHEA with a BCC/B2 dual-phase structure is successfully developed.The RHEA exhibits excellent specifc yield strength of 162.4 MPa·g^(−1)·cm^(3) and 84.3 MPa·g^(−1)·cm^(3) at room temperature(RT)and 800℃,respectively.It was found that the pinning efect of the B2 phase induces a gradual transition in dislocation slip mode from planar slip to cross slip,homogenizing the plastic fow and resulting in excellent compression plasticity(ε>50%).Additionally,the B2 phase endows the alloy with excellent yield strength at high temperatures by precipitation strengthening.Moreover,the dominated a/2<111>type dislocation contributes to the alloy's superior plasticity at high temperatures.展开更多
B2-CuZr phase reinforced amorphous alloy matrix composites has become one of the research hotspots in the field of materials science due to the“transformation-induced plasticity”phenomenon,which makes the composites...B2-CuZr phase reinforced amorphous alloy matrix composites has become one of the research hotspots in the field of materials science due to the“transformation-induced plasticity”phenomenon,which makes the composites show better macroscopic plastic deformability and obvious work-hardening behavior compared to the conventional amorphous alloy matrix composites reinforced with ductile phases.However,the in-situ metastable B2-CuZr phase tends to undergo eutectoid decomposition during solidification,and the volume fraction,size,and distribution of B2-CuZr phase are difficult to control,which limits the development and application of these materials.To date,much efforts have been made to solve the above problems through composition optimization,casting parameter tailoring,and post-processing technique.In this study,a review was given based on relevant studies,focusing on the predictive approach,reinforcing mechanism,and microstructure tailoring methods of B2-CuZr phase reinforced amorphous alloy matrix composites.The research focus and future prospects were also given for the future development of the present composite system.展开更多
Based on the analyses of the microstructures and phase diagrams of the TiAl-based alloy, the relationship among the composition, structure and mechanical properties of the B2-containing y-TiAI alloys was reviewed. The...Based on the analyses of the microstructures and phase diagrams of the TiAl-based alloy, the relationship among the composition, structure and mechanical properties of the B2-containing y-TiAI alloys was reviewed. The refinement of microstructures and improvement of mechanical properties of TiA1 alloy through stabilization of the β/B2 phase were reviewed. The mechanism of the superplastic behavior of the B2-containing y-TiAI alloys was discussed. With a reasonable addition of β-stabilizer, metastable B2 phase can be maintained, which is favorable for fine-grained structure and better high-temperature deformation behaviors. The mechanical properties of the B2-containing TiAI alloy, including the deformability and elevated temperature properties, can also be improved with doping elements and subsequent hot-working processes. The above mentioned researches discuss a new way for developing TiAI alloys with comprehensive properties, including good deformability and creep resistance.展开更多
Precipitation-hardening in fcc-based high-entro py alloys(HEAs)have usually been realized by introducing complex intermetallic compounds.In this study,enhanced strength is ascribed to the existence of L1_(2) precipita...Precipitation-hardening in fcc-based high-entro py alloys(HEAs)have usually been realized by introducing complex intermetallic compounds.In this study,enhanced strength is ascribed to the existence of L1_(2) precipitates and B2/bcc conjoint phases in the fcc matrix.The nano-size particles in the Al_(0.5)CoCrFeNi HEA are produced by cold-rolling,followed by intermediate-temperature-annealing at 650℃.For L1_(2) ordering,the initial granular structure has transformed into lamella structure and then kept stable when the holding time prolonged to 200 h.The formation of this conjoint B2/bcc driven by the concentration profiles takes place when the diffusion process of elements is sufficient after long-time aging.Based on the microstructure analysis,changes in mechanical properties are associated with the shape,size scale and volume fraction of the precipitates.The peak ultimate tensile stress reaches 1221.5 MPa,1.97 times compared with the as-cast alloy,remaining plasticity of 21.3%.展开更多
Adding Al is an important strategy to obtain ultrahigh specific strength in BCC refractory high-entropy alloys(RHEAs).However,the main structure typically transitions from disordered BCC to ordered B2 with increasing ...Adding Al is an important strategy to obtain ultrahigh specific strength in BCC refractory high-entropy alloys(RHEAs).However,the main structure typically transitions from disordered BCC to ordered B2 with increasing Al concentration,leading to poor ductility.In the present study,a phase inversion in a high-Al-content B2-RHEA(Zr_(40)Ti_(28)Nb_(12)Al_(20))was systematically studied through thermo-mechanical treatment.The grains of the single B2 phase transformed inversely to the BCC+B2 microstructure with a dispersion of spherical B2 precipitates in the BCC grains.The evolution of the microstructure began with the decomposition of the B2 phase into Al-rich and Al-poor regions.The subsequent coarsening of the Al-rich B2 precipitates continuously consumes Al and Zr atoms from the solution.The depletion of Al and Zr in the matrix drives it to gradually form the disordered BCC structure and eventually transform to a single BCC phase matrix.This phase inversion enhanced tensile ductility of the RHEA while still maintaining its high specific strength.The current study provides a novel idea for inhibiting Al-induced brittleness of RHEAs at high Al content.展开更多
The segregation and diffusion of boron during heat treatments were studied. The influence of boron contents, aging time and applied stress on FeMo2B2 formation was also studied. Finally, the effects of boron contents ...The segregation and diffusion of boron during heat treatments were studied. The influence of boron contents, aging time and applied stress on FeMo2B2 formation was also studied. Finally, the effects of boron contents and FeMo2B2 formation on the high temperature strength were studied. Boron atoms were segregated to prior austenite grain boundary during normalizing treatment. And these boron atoms were slowly diffused into the grain interior during tempering and aging at 700 ℃. The FeMo2B2 phase was only formed after 1,000 h aging at 700 ℃ in alloy containing 196 ppm boron. The formation of FeMo2B2 phase is accelerated by the applied stress. It was expected that the formation of FeMo2B2 is closely related to the redistribution of boron atoms. The tensile strengths at 700 ℃ are increased with the increase of boron contents. However, the formation of FeMo2B2 phase results in lower tensile strength.展开更多
基金supported by the Chinese Academy of Sciences(ZDBS-LY-JSC023)the National Natural Science Foundation of China(No.52404370)+3 种基金the Natural Science Foundation of Liaoning Province(2023-BS-012)the Youth Innovation Promotion Association CAS(2021188)the IMR Innovation Fund(2023-PY16)the Guangdong Basic and Applied Basic Research Foundation(2023A1515111060).
文摘Refractory high-entropy alloys(RHEAs)stand as promising candidates for the development of a new generation of hightemperature materials due to their exceptional mechanical properties.However,the inherent low ductility and high density of RHEAs have hindered their widespread adoption in industrial applications.In this study,an Nb_(38)Ti_(35)Al_(15)V_(6)Cr_(4)(TaHfMoW)_(2) RHEA with a BCC/B2 dual-phase structure is successfully developed.The RHEA exhibits excellent specifc yield strength of 162.4 MPa·g^(−1)·cm^(3) and 84.3 MPa·g^(−1)·cm^(3) at room temperature(RT)and 800℃,respectively.It was found that the pinning efect of the B2 phase induces a gradual transition in dislocation slip mode from planar slip to cross slip,homogenizing the plastic fow and resulting in excellent compression plasticity(ε>50%).Additionally,the B2 phase endows the alloy with excellent yield strength at high temperatures by precipitation strengthening.Moreover,the dominated a/2<111>type dislocation contributes to the alloy's superior plasticity at high temperatures.
基金supported by the National Natural Science Foundation of China(No.52101138,No.52201075)the Natural Science Foundation of Hubei Province(No.2023AFB798,No.2022CFB614)+3 种基金the Shenzhen Science and Technology Program(No.JCYJ20220530160813032)the State Key Laboratory of Solidification Processing in NWPU(No.SKLSP202309,No.SKLSP202308)the Guangdong Basic and Applied Basic Research Foundation(No.2022A1515011227)the State Key Laboratory of Powder Metallurgy of Central South University(No.SklpmKF-05)。
文摘B2-CuZr phase reinforced amorphous alloy matrix composites has become one of the research hotspots in the field of materials science due to the“transformation-induced plasticity”phenomenon,which makes the composites show better macroscopic plastic deformability and obvious work-hardening behavior compared to the conventional amorphous alloy matrix composites reinforced with ductile phases.However,the in-situ metastable B2-CuZr phase tends to undergo eutectoid decomposition during solidification,and the volume fraction,size,and distribution of B2-CuZr phase are difficult to control,which limits the development and application of these materials.To date,much efforts have been made to solve the above problems through composition optimization,casting parameter tailoring,and post-processing technique.In this study,a review was given based on relevant studies,focusing on the predictive approach,reinforcing mechanism,and microstructure tailoring methods of B2-CuZr phase reinforced amorphous alloy matrix composites.The research focus and future prospects were also given for the future development of the present composite system.
基金Project (2011CB605505) supported by the National Basic Research Program of ChinaProject (2011JQ002) supported by the Fundamental Research Funds for the Central Universities, China
文摘Based on the analyses of the microstructures and phase diagrams of the TiAl-based alloy, the relationship among the composition, structure and mechanical properties of the B2-containing y-TiAI alloys was reviewed. The refinement of microstructures and improvement of mechanical properties of TiA1 alloy through stabilization of the β/B2 phase were reviewed. The mechanism of the superplastic behavior of the B2-containing y-TiAI alloys was discussed. With a reasonable addition of β-stabilizer, metastable B2 phase can be maintained, which is favorable for fine-grained structure and better high-temperature deformation behaviors. The mechanical properties of the B2-containing TiAI alloy, including the deformability and elevated temperature properties, can also be improved with doping elements and subsequent hot-working processes. The above mentioned researches discuss a new way for developing TiAI alloys with comprehensive properties, including good deformability and creep resistance.
基金supported financially by the National Natural Science Foundation of China(Nos.51774240 and 51571161)the fund of the State Key Laboratory of Solidification Processing in NWPU(No.2019-TS-04)the National Training Program of Innovation and Entrepreneurship for Undergraduates(No.201910699109)。
文摘Precipitation-hardening in fcc-based high-entro py alloys(HEAs)have usually been realized by introducing complex intermetallic compounds.In this study,enhanced strength is ascribed to the existence of L1_(2) precipitates and B2/bcc conjoint phases in the fcc matrix.The nano-size particles in the Al_(0.5)CoCrFeNi HEA are produced by cold-rolling,followed by intermediate-temperature-annealing at 650℃.For L1_(2) ordering,the initial granular structure has transformed into lamella structure and then kept stable when the holding time prolonged to 200 h.The formation of this conjoint B2/bcc driven by the concentration profiles takes place when the diffusion process of elements is sufficient after long-time aging.Based on the microstructure analysis,changes in mechanical properties are associated with the shape,size scale and volume fraction of the precipitates.The peak ultimate tensile stress reaches 1221.5 MPa,1.97 times compared with the as-cast alloy,remaining plasticity of 21.3%.
基金support from the National Key Research and Development Program of China (No.2017YFB0702003)the National Natural Science Foundation of China (No.51871217)+2 种基金Yong Zhang thanks the Guangdong Basic and Applied Basic Research Foundation (No.2019B1515120020)the State Key Laboratory for Advanced Metals and Materials in the University of Science and Technology Beijing (No.2020Z-08)the Funds for Creative Research Groups of China (No.51921001).
文摘Adding Al is an important strategy to obtain ultrahigh specific strength in BCC refractory high-entropy alloys(RHEAs).However,the main structure typically transitions from disordered BCC to ordered B2 with increasing Al concentration,leading to poor ductility.In the present study,a phase inversion in a high-Al-content B2-RHEA(Zr_(40)Ti_(28)Nb_(12)Al_(20))was systematically studied through thermo-mechanical treatment.The grains of the single B2 phase transformed inversely to the BCC+B2 microstructure with a dispersion of spherical B2 precipitates in the BCC grains.The evolution of the microstructure began with the decomposition of the B2 phase into Al-rich and Al-poor regions.The subsequent coarsening of the Al-rich B2 precipitates continuously consumes Al and Zr atoms from the solution.The depletion of Al and Zr in the matrix drives it to gradually form the disordered BCC structure and eventually transform to a single BCC phase matrix.This phase inversion enhanced tensile ductility of the RHEA while still maintaining its high specific strength.The current study provides a novel idea for inhibiting Al-induced brittleness of RHEAs at high Al content.
基金This work was financially supported by the Ministry of Commerce,Industry and Energy of Korea.
文摘The segregation and diffusion of boron during heat treatments were studied. The influence of boron contents, aging time and applied stress on FeMo2B2 formation was also studied. Finally, the effects of boron contents and FeMo2B2 formation on the high temperature strength were studied. Boron atoms were segregated to prior austenite grain boundary during normalizing treatment. And these boron atoms were slowly diffused into the grain interior during tempering and aging at 700 ℃. The FeMo2B2 phase was only formed after 1,000 h aging at 700 ℃ in alloy containing 196 ppm boron. The formation of FeMo2B2 phase is accelerated by the applied stress. It was expected that the formation of FeMo2B2 is closely related to the redistribution of boron atoms. The tensile strengths at 700 ℃ are increased with the increase of boron contents. However, the formation of FeMo2B2 phase results in lower tensile strength.
