The concept of grain boundary engineering(GBE)has been successfully applied to L1_(2)-strengthened(CoCrNi)_(94)Al_(3)Ti_(3)medium entropy alloy,with the aim of improving the oxidation resistance by increasing the rati...The concept of grain boundary engineering(GBE)has been successfully applied to L1_(2)-strengthened(CoCrNi)_(94)Al_(3)Ti_(3)medium entropy alloy,with the aim of improving the oxidation resistance by increasing the ratio of special boundaries and suppressing discontinuous precipitation.Surprisingly,our results reveal that GBE treatment not only slows down the oxidation kinetics and but also alters the oxide scale from TiO_(2)and multi-defect Cr_(2)O_(3)to continuous and protective Cr_(2)O_(3)and Al_(2)O_(3),thereby contributing to an enhanced oxidation and anti-spalling resistance.The GBE treatment reduces the oxidation weight gain of the current alloy from 1.950 mg cm^(-2)to 1.211 mg cm^(-2)after 100 h of cyclic oxidation at 800℃.The findings show that the extensive outward diffusion of Ti accelerates ion transport and promotes microporosity,thus leading to more defects being formed in the oxide film.The GBE treatment suppresses the discontinuous precipitation of the Ti-bearing L1_(2)phase and breaks the random large angular grain boundaries network,inhibiting the diffusion of Ti and ultimately enhancing the oxidation properties of the alloy.The current work provides an idea of oxidation resistance enhancement for Ti-bearing LI_(2)-strengthened alloys without changing the alloy composition.展开更多
Gas atomization is now an important production technique for Fe-based amorphous alloy powders used in additive manufacturing,particularly selective laser melting,fabricating large-sized Fe-based bulk metallic glasses....Gas atomization is now an important production technique for Fe-based amorphous alloy powders used in additive manufacturing,particularly selective laser melting,fabricating large-sized Fe-based bulk metallic glasses.Using the realizable k-εmodel and discrete phase model theory,the flow dynamics of the gas phase and gas-melt two-phase flow felds in the close-wake condition were investigated to establish the correlation between high gas pressure and powder particle characteristics.The locations of the recirculation zones and the shapes of Mach disks were analyzed in detail for the type of discrete-jet closed-coupled gas atomization nozzle.In the gas-phase flow feld,the vortexes,closed to the Mach disk,are found to be a new deceleration method.In the two-phase flow feld,the shape of Mach disk changes from“S”-shape to“Z”-shape under the impact of the droplet flow.As predicted by the wave model,with the elevation of gas pressure,the size of the particle is found to gradually decrease and its distribution becomes more concentrated.Simulation results were compliant with the Fe-based amorphous alloy powder preparation tests.This study deepens the understanding of the gas pressure impacting particle features via gas atomization,and contributes to technological applications.展开更多
Although refractory high-entropy alloys(RHEAs)possess excellent softening resistance and thermal sta-bility at high temperatures,their practical application is often limited due to room temperature(RT)brit-tleness.In ...Although refractory high-entropy alloys(RHEAs)possess excellent softening resistance and thermal sta-bility at high temperatures,their practical application is often limited due to room temperature(RT)brit-tleness.In this work,we successfully achieved RT plasticization in a brittle(TaMoTi)_(92)Al_(8)RHEA via in situ forming heterogeneous structure(HS)with the doping of Zr.Different from the mainstream design con-cept of“soft solid solution matrices with hard intermetallic phases”proposed in the literature,the newly developed TaMoZrTiAl RHEA is featured by a hard disordered BCC phase embedded into a soft intermetal-lic B2 matrix.Such an HS leads to the remarkable strength-plasticity synergy in this alloy at RT,showing a large plasticity of>20%,associated with a high strength of>2380 MPa.It was found that solid solu-tion strengthening and heterodeformation-induced strengthening caused by dislocation pile-ups at phase boundaries are responsible for the enhancement in the yield strength,while deformation-induced strain partition and the frequent operation of dislocation cross-slip substantially improve the work hardening capacity of alloy,thus enabling the high strength and good RT plasticity.In short,the current work not only reveals the micromechanisms of the influence of heterogeneous dual-phase structure on the RT me-chanical behaviour in RHEAs but also provides a useful strategy for plasticizing brittle RHEAs.展开更多
A new Al-based composite consisting of submicron-sized α-Al matrix embedded with precipitated intermetallic phases was developed by controlling the devitrification process of an Al-Ni-Y-Co-La amorphous alloy.Such a h...A new Al-based composite consisting of submicron-sized α-Al matrix embedded with precipitated intermetallic phases was developed by controlling the devitrification process of an Al-Ni-Y-Co-La amorphous alloy.Such a homogeneous composite structure presented an ultrahigh strength of about 1.34 GPa and a large compressive plastic strain up to 22%.The unique mechanical properties during compression are mainly attributed to the dislocation slip deformation of ductile a-AI matrix and the shear-induced refinement of strengthening intermetallic phases.展开更多
To clarify the deformation behavior of Al-rich metallic glasses（MGs）, two kinds of Al-rich MGs（i.e. bulk and ribbon samples） with different frozen-in excess volume have been analyzed under nanoindentation.It was f...To clarify the deformation behavior of Al-rich metallic glasses（MGs）, two kinds of Al-rich MGs（i.e. bulk and ribbon samples） with different frozen-in excess volume have been analyzed under nanoindentation.It was found that, with the decrease of frozen-in excess volume, the serration behavior becomes inconspicuous together with the increase of hardness. Further, shear transformation zones（STZs）, related to the occurrence of shear banding, have been evaluated by different methods： the cooperative shearing model（CSM）, the rate-jump method（RJM） and the dynamic-mechanical response（DMR）. In contrast,the STZ volumes, calculated by the RJM, increase from 2.77 nm^3 in the bulk to 3.59 nm^3 in the ribbon,which are in good agreement with 2.60 nm^3 obtained from the icosahedral supercluster medium-range order structure model in Al-rich MGs. This result reflects that an intrinsic correlation exists between the formation of STZs and the medium-range orders（MROs）. Moreover, the variation trend of the STZ volume was analyzed in terms of the frozen-in excess volume content.展开更多
基金the National Natural Science Foundation of China(Nos.U1908219,52171163)the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-CN-2021-2-2)+2 种基金the National key Research&Development Program of China(No.2022YFF0609002)the Natural Science Foundation of Liaoning Province(No.2022-BS-001)China Postdoctoral Science Foundation(No.2022M713210)。
文摘The concept of grain boundary engineering(GBE)has been successfully applied to L1_(2)-strengthened(CoCrNi)_(94)Al_(3)Ti_(3)medium entropy alloy,with the aim of improving the oxidation resistance by increasing the ratio of special boundaries and suppressing discontinuous precipitation.Surprisingly,our results reveal that GBE treatment not only slows down the oxidation kinetics and but also alters the oxide scale from TiO_(2)and multi-defect Cr_(2)O_(3)to continuous and protective Cr_(2)O_(3)and Al_(2)O_(3),thereby contributing to an enhanced oxidation and anti-spalling resistance.The GBE treatment reduces the oxidation weight gain of the current alloy from 1.950 mg cm^(-2)to 1.211 mg cm^(-2)after 100 h of cyclic oxidation at 800℃.The findings show that the extensive outward diffusion of Ti accelerates ion transport and promotes microporosity,thus leading to more defects being formed in the oxide film.The GBE treatment suppresses the discontinuous precipitation of the Ti-bearing L1_(2)phase and breaks the random large angular grain boundaries network,inhibiting the diffusion of Ti and ultimately enhancing the oxidation properties of the alloy.The current work provides an idea of oxidation resistance enhancement for Ti-bearing LI_(2)-strengthened alloys without changing the alloy composition.
基金supported by the National Key Research and Development Program of China(No.2016YFB1100204)the Key Research&Development Plan of Jiangxi Province(No.20192ACB80001)the National Natural Science Foundation of China(Nos.52171163,51701214 and U1908219)。
文摘Gas atomization is now an important production technique for Fe-based amorphous alloy powders used in additive manufacturing,particularly selective laser melting,fabricating large-sized Fe-based bulk metallic glasses.Using the realizable k-εmodel and discrete phase model theory,the flow dynamics of the gas phase and gas-melt two-phase flow felds in the close-wake condition were investigated to establish the correlation between high gas pressure and powder particle characteristics.The locations of the recirculation zones and the shapes of Mach disks were analyzed in detail for the type of discrete-jet closed-coupled gas atomization nozzle.In the gas-phase flow feld,the vortexes,closed to the Mach disk,are found to be a new deceleration method.In the two-phase flow feld,the shape of Mach disk changes from“S”-shape to“Z”-shape under the impact of the droplet flow.As predicted by the wave model,with the elevation of gas pressure,the size of the particle is found to gradually decrease and its distribution becomes more concentrated.Simulation results were compliant with the Fe-based amorphous alloy powder preparation tests.This study deepens the understanding of the gas pressure impacting particle features via gas atomization,and contributes to technological applications.
基金supported by the National Key Research&De-velopment Program of China(No.2022YFF0609002)the National Natural Science Foundation of China(Nos.U1908219,52171163,and 52271157)+4 种基金the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-CN-2021-2-2)the key Research&Devel-opment Plan of Jiangxi Province(No.20192ACB80001)the Natu-ral Science Foundation of Liaoning Province(No.2022-BS-001)the China Postdoctoral Science Foundation(No.2022M713210)the Shenyang National Laboratory for Materials Science.
文摘Although refractory high-entropy alloys(RHEAs)possess excellent softening resistance and thermal sta-bility at high temperatures,their practical application is often limited due to room temperature(RT)brit-tleness.In this work,we successfully achieved RT plasticization in a brittle(TaMoTi)_(92)Al_(8)RHEA via in situ forming heterogeneous structure(HS)with the doping of Zr.Different from the mainstream design con-cept of“soft solid solution matrices with hard intermetallic phases”proposed in the literature,the newly developed TaMoZrTiAl RHEA is featured by a hard disordered BCC phase embedded into a soft intermetal-lic B2 matrix.Such an HS leads to the remarkable strength-plasticity synergy in this alloy at RT,showing a large plasticity of>20%,associated with a high strength of>2380 MPa.It was found that solid solu-tion strengthening and heterodeformation-induced strengthening caused by dislocation pile-ups at phase boundaries are responsible for the enhancement in the yield strength,while deformation-induced strain partition and the frequent operation of dislocation cross-slip substantially improve the work hardening capacity of alloy,thus enabling the high strength and good RT plasticity.In short,the current work not only reveals the micromechanisms of the influence of heterogeneous dual-phase structure on the RT me-chanical behaviour in RHEAs but also provides a useful strategy for plasticizing brittle RHEAs.
基金supported by the National Natural Science Foundation of China(Grant Nos.51131006,51071151)
文摘A new Al-based composite consisting of submicron-sized α-Al matrix embedded with precipitated intermetallic phases was developed by controlling the devitrification process of an Al-Ni-Y-Co-La amorphous alloy.Such a homogeneous composite structure presented an ultrahigh strength of about 1.34 GPa and a large compressive plastic strain up to 22%.The unique mechanical properties during compression are mainly attributed to the dislocation slip deformation of ductile a-AI matrix and the shear-induced refinement of strengthening intermetallic phases.
基金supported by the National Natural Science Foundation of China (Nos. 51131006 and 51471166)the National Key Research and Development Program of China (No. 2016YFB1100204)
文摘To clarify the deformation behavior of Al-rich metallic glasses（MGs）, two kinds of Al-rich MGs（i.e. bulk and ribbon samples） with different frozen-in excess volume have been analyzed under nanoindentation.It was found that, with the decrease of frozen-in excess volume, the serration behavior becomes inconspicuous together with the increase of hardness. Further, shear transformation zones（STZs）, related to the occurrence of shear banding, have been evaluated by different methods： the cooperative shearing model（CSM）, the rate-jump method（RJM） and the dynamic-mechanical response（DMR）. In contrast,the STZ volumes, calculated by the RJM, increase from 2.77 nm^3 in the bulk to 3.59 nm^3 in the ribbon,which are in good agreement with 2.60 nm^3 obtained from the icosahedral supercluster medium-range order structure model in Al-rich MGs. This result reflects that an intrinsic correlation exists between the formation of STZs and the medium-range orders（MROs）. Moreover, the variation trend of the STZ volume was analyzed in terms of the frozen-in excess volume content.
