Ultra-high strength alloys with good ductility are ideal materials for lightweight structural application in various industries. However, improving the strength of alloys frequently results in a reduction in ductility...Ultra-high strength alloys with good ductility are ideal materials for lightweight structural application in various industries. However, improving the strength of alloys frequently results in a reduction in ductility, which is known as the strength-ductility trade-off in metallic materials. Current alloy design strategies for improving the ductility of ultra-high strength alloys mainly focus on the selection of alloy composition （atomic length scale） or manipulating ultra-fine and nano-grained microstructure （grain length scale）. The intermediate length scale between atomic and grain scales is the dislocation length scale. A new alloy design concept based on such dislocation length scale, namely dislocation engineering, is illustrated in the present work. This dislocation engineering concept has been successfully substantiated by the design and fabrication of a deformed and partitioned （D＆P） steel with a yield strength of 2,2 GPa and an uniform elongation of 16%. In this D＆P steel, high dislocation density can not only increase strength but also improve ductility. High dislocation density is mainly responsible for the improved yield strength through dislocation forest hardening, whilst the improved ductility is achieved by the glide of intensive mobile dislocations and well-controlled transformation-induced plasticity （TRIP） effect, both of which are governed by the high dislocation density resulting from warm rolling and martensitic transformation during cold rolling. In addition, the present work proposes for the first time to apply such dislocation engineering concept to the quenching and partitioning （Q＆P） steel by incorporating a warm rolling process prior to the quenching step, with an aim to improve simultaneously the strength and ductility of the Q＆P steel. It is believed that dislocation engineering provides a new promising alloy design strategy for producing novel strong and ductile alloys.展开更多
Most inorganic thermoelectric semiconductors are intrinsically brittle,restricting the application of ther-moelectric materials.Therefore,developing ductile thermoelectric materials is crucial to thermoelectric techno...Most inorganic thermoelectric semiconductors are intrinsically brittle,restricting the application of ther-moelectric materials.Therefore,developing ductile thermoelectric materials is crucial to thermoelectric technology applications.In this work,single-phase SnTe bulks with dense dislocations were prepared by melting quenching combined with spark plasma sintering.The resulting SnTe thermoelectric materials exhibited a large compressive strain of∼7.5%at room temperature,originating from high-density pre-existing mobile dislocations.The initiation of localized slip bands and preferred slip system were also identified by first-principles simulation.Detail microstructural characterizations reveal that the thermal activated dislocation emission and migration lead to higher compressive strains at intermediate tem-peratures.At 673 K,the deformation mechanism changed from dislocation mediated to grain boundary mediated plasticity,resulting in an ultra-high compressive strain of∼42%.In sum,new insights into the mechanical behavior of SnTe thermoelectric material over a wide range of temperatures were provided.This work offers the dislocation engineering strategy to design ductile thermoelectric materials for flexi-ble electronics and energy systems.展开更多
By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic slip and the pyramidal <c+a> slip occur during the tensile process at room temperature, which ...By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic slip and the pyramidal <c+a> slip occur during the tensile process at room temperature, which finally leads to the plenty of dislocation accumulation. After 8% tensile deformation,the {1012} extension twin is the main way to coordinate the strain in the c-axis direction for the alloy with the Ga content lower than 2 wt.%, but the pyramidal <c+a> slip is the main way to coordinate the strain along the c-axis direction for the alloy with the Ga content higher than 2 wt.%. The Ga addition can promote the activation of the non-basal slip, which is beneficial to the work-hardening of the alloy to achieve better plasticity. Dynamic precipitation can slightly reduce the increment of dislocations.The preparation method of high strain rate rolling(HSRR) is another important reason for the plasticity of magnesium alloy sheets, and it is an important embodiment of the application of the dislocation engineering concept in magnesium alloy. The non-basal dislocations derived from the HSRR deformation can provide the non-basal dislocation sources when magnesium alloy is deformed at room temperature,resulting in good ductility. This study can be used as a reference for preparing wrought magnesium alloy with high strength and high plasticity by Ga alloying and hot deformation.展开更多
Achieving high superelasticity in polycrystalline shape memory alloys is fundamentally limited by strain incompatibilities arising from grain orientation.Realizing high martensitic transformation strain(εTS)orientati...Achieving high superelasticity in polycrystalline shape memory alloys is fundamentally limited by strain incompatibilities arising from grain orientation.Realizing high martensitic transformation strain(εTS)orientations that are favorable for superelasticity in equiaxed microstructures remains a major challenge.Here,a novel heterogeneity-driven texture optimization strategy is reported to enhance superelasticity in CuAlMn alloys through controlling high-εTS orientations.Controlled deformation imprints dislocation density heterogeneity in differently oriented grains,leading to the gradients of sub-boundary energy.These gradients drive selective grain boundary migration,facilitating the preferential growth of grains with the high-εTS<015>orientation.As a result,the fraction of<015>-oriented grains increases significantly from∼19%to∼70%,yielding a unprecedent tensile superelastic strain of∼8.0%in equiaxed CuAlMn alloys,paving the way for practical engineering applications.This microstructural heterogeneity-guided strategy offers a general framework for overcoming texture-related limitations in polycrystalline functional materials.展开更多
基金the support from Research Grants Council of Hong Kong (Grants No. 17203014, HKU712713E and 17255016)the National Natural Science Foundation of China (Grant No. U1560204)
文摘Ultra-high strength alloys with good ductility are ideal materials for lightweight structural application in various industries. However, improving the strength of alloys frequently results in a reduction in ductility, which is known as the strength-ductility trade-off in metallic materials. Current alloy design strategies for improving the ductility of ultra-high strength alloys mainly focus on the selection of alloy composition （atomic length scale） or manipulating ultra-fine and nano-grained microstructure （grain length scale）. The intermediate length scale between atomic and grain scales is the dislocation length scale. A new alloy design concept based on such dislocation length scale, namely dislocation engineering, is illustrated in the present work. This dislocation engineering concept has been successfully substantiated by the design and fabrication of a deformed and partitioned （D＆P） steel with a yield strength of 2,2 GPa and an uniform elongation of 16%. In this D＆P steel, high dislocation density can not only increase strength but also improve ductility. High dislocation density is mainly responsible for the improved yield strength through dislocation forest hardening, whilst the improved ductility is achieved by the glide of intensive mobile dislocations and well-controlled transformation-induced plasticity （TRIP） effect, both of which are governed by the high dislocation density resulting from warm rolling and martensitic transformation during cold rolling. In addition, the present work proposes for the first time to apply such dislocation engineering concept to the quenching and partitioning （Q＆P） steel by incorporating a warm rolling process prior to the quenching step, with an aim to improve simultaneously the strength and ductility of the Q＆P steel. It is believed that dislocation engineering provides a new promising alloy design strategy for producing novel strong and ductile alloys.
基金supported by the National Natural Science Foundation of China (Nos.52171220,51972253,92163119 and 92163212)the Fundamental Research Funds for the Central Universities (Nos.WUT:2020-YB-037,2022IVA059 and 2022IVA141)supported by the Fundamental Re-search Funds for the Central Universities (No.WUT:2019III012GX).
文摘Most inorganic thermoelectric semiconductors are intrinsically brittle,restricting the application of ther-moelectric materials.Therefore,developing ductile thermoelectric materials is crucial to thermoelectric technology applications.In this work,single-phase SnTe bulks with dense dislocations were prepared by melting quenching combined with spark plasma sintering.The resulting SnTe thermoelectric materials exhibited a large compressive strain of∼7.5%at room temperature,originating from high-density pre-existing mobile dislocations.The initiation of localized slip bands and preferred slip system were also identified by first-principles simulation.Detail microstructural characterizations reveal that the thermal activated dislocation emission and migration lead to higher compressive strains at intermediate tem-peratures.At 673 K,the deformation mechanism changed from dislocation mediated to grain boundary mediated plasticity,resulting in an ultra-high compressive strain of∼42%.In sum,new insights into the mechanical behavior of SnTe thermoelectric material over a wide range of temperatures were provided.This work offers the dislocation engineering strategy to design ductile thermoelectric materials for flexi-ble electronics and energy systems.
基金financially supported by the National Natural Science Foundation of China (no. 51871093)the Natural Science Foundation of Hunan Province, China (no. 2019JJ40044)。
文摘By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic slip and the pyramidal <c+a> slip occur during the tensile process at room temperature, which finally leads to the plenty of dislocation accumulation. After 8% tensile deformation,the {1012} extension twin is the main way to coordinate the strain in the c-axis direction for the alloy with the Ga content lower than 2 wt.%, but the pyramidal <c+a> slip is the main way to coordinate the strain along the c-axis direction for the alloy with the Ga content higher than 2 wt.%. The Ga addition can promote the activation of the non-basal slip, which is beneficial to the work-hardening of the alloy to achieve better plasticity. Dynamic precipitation can slightly reduce the increment of dislocations.The preparation method of high strain rate rolling(HSRR) is another important reason for the plasticity of magnesium alloy sheets, and it is an important embodiment of the application of the dislocation engineering concept in magnesium alloy. The non-basal dislocations derived from the HSRR deformation can provide the non-basal dislocation sources when magnesium alloy is deformed at room temperature,resulting in good ductility. This study can be used as a reference for preparing wrought magnesium alloy with high strength and high plasticity by Ga alloying and hot deformation.
基金supported by the National Key Research and Development Project(2020YFE0202600)the NSFC Funding(U2141207).
文摘Achieving high superelasticity in polycrystalline shape memory alloys is fundamentally limited by strain incompatibilities arising from grain orientation.Realizing high martensitic transformation strain(εTS)orientations that are favorable for superelasticity in equiaxed microstructures remains a major challenge.Here,a novel heterogeneity-driven texture optimization strategy is reported to enhance superelasticity in CuAlMn alloys through controlling high-εTS orientations.Controlled deformation imprints dislocation density heterogeneity in differently oriented grains,leading to the gradients of sub-boundary energy.These gradients drive selective grain boundary migration,facilitating the preferential growth of grains with the high-εTS<015>orientation.As a result,the fraction of<015>-oriented grains increases significantly from∼19%to∼70%,yielding a unprecedent tensile superelastic strain of∼8.0%in equiaxed CuAlMn alloys,paving the way for practical engineering applications.This microstructural heterogeneity-guided strategy offers a general framework for overcoming texture-related limitations in polycrystalline functional materials.
