Ultrafine-grained(UFG)materials exhibit high strengths due to grain boundary strengthening,but grains can grow rapidly if post heat treatment is required,making it challenging to achieve grain boundary and precipitati...Ultrafine-grained(UFG)materials exhibit high strengths due to grain boundary strengthening,but grains can grow rapidly if post heat treatment is required,making it challenging to achieve grain boundary and precipitation strengthening simultaneously.Grain growth stagnation at 525℃(0.87 T_(m),melting point)was observed in a Mg-4Y-3RE alloy fabricated by additive friction stir deposition(AFSD),a novel solidstate additive manufacturing technology.The AFSD processing produced a UFG microstructure and two major second phases,Mg_(41)RE_(5)and nanoparticles containing Y and O.After solid solution treatment(SST)at 525℃for 72 h,no noticeable grain growth occurred.While Mg_(41)RE_(5)particles dissolved into the matrix within 4 h of SST,the nanoparticles remained stable and unaltered.The observed grain growth stagnation is attributed to Zener pinning by these thermally stable nanoparticles.These new findings offer a novel approach to designing UFG materials with exceptional thermal stability for high-temperature applications.展开更多
Realizing high work hardening and thus elevated strength–ductility synergy are prerequisites for the practical usage of body-centered-cubic high entropy alloys(BCC-HEAs).In this study,we report a novel dynamic streng...Realizing high work hardening and thus elevated strength–ductility synergy are prerequisites for the practical usage of body-centered-cubic high entropy alloys(BCC-HEAs).In this study,we report a novel dynamic strengthening mechanism,martensitic twinning transformation mechanism in a metastable refractory element-based BCC-HEA(TiZrHf)Ta(at.%)that can profoundly enhance the work hardening capability,leading to a large uniform ductility and high strength simultaneously.Different from conventional transformation induced plasticity(TRIP)and twinning induced plasticity(TWIP)strengthening mechanisms,the martensitic twinning transformation strengthening mechanism combines the best characteristics of both TRIP and TWIP strengthening mechanisms,which greatly alleviates the strengthductility trade-off that ubiquitously observed in BCC structural alloys.Microstructure characterization,carried out using X-ray diffraction(XRD)and electron back-scatter diffraction(EBSD)shows that,upon straining,α”(orthorhombic)martensite transformation,self-accommodation(SA)α”twinning and mechanicalα”twinning were activated sequentially.Transmission electron microscopy(TEM)analyses reveal that continuous twinning activation is inherited from nucleating mechanical{351}type I twins within SA“{351}”<■11>typeⅡtwinnedα”variants on{351}twinning plane by twinning transformation through simple shear,thereby accommodating the excessive plastic strain through the twinning shear while concurrently refining the grain structure.Consequently,consistent high work hardening rates of 2–12.5 GPa were achieved during the entire plastic deformation,leading to a high tensile strength of 1.3 GPa and uniform elongation of 24%.Alloy development guidelines for activating such martensitic twinning transformation strengthening mechanism were proposed,which could be important in developing new BCC-HEAs with optimal mechanical performance.展开更多
基金supported by the UKRI Future Leaders Fellowship,[MR/T019123/2]。
文摘Ultrafine-grained(UFG)materials exhibit high strengths due to grain boundary strengthening,but grains can grow rapidly if post heat treatment is required,making it challenging to achieve grain boundary and precipitation strengthening simultaneously.Grain growth stagnation at 525℃(0.87 T_(m),melting point)was observed in a Mg-4Y-3RE alloy fabricated by additive friction stir deposition(AFSD),a novel solidstate additive manufacturing technology.The AFSD processing produced a UFG microstructure and two major second phases,Mg_(41)RE_(5)and nanoparticles containing Y and O.After solid solution treatment(SST)at 525℃for 72 h,no noticeable grain growth occurred.While Mg_(41)RE_(5)particles dissolved into the matrix within 4 h of SST,the nanoparticles remained stable and unaltered.The observed grain growth stagnation is attributed to Zener pinning by these thermally stable nanoparticles.These new findings offer a novel approach to designing UFG materials with exceptional thermal stability for high-temperature applications.
基金Engineering and Physical Sciences Research Council(EPSRC)(No.EP/P006566/1)under Manufacture using Advanced Powder Processes(MAPP)the Henry Royce Institute for Advanced Materials,funded through EPSRC(Nos.EP/R00661X/1,EP/S019367/1,EP/P02470X/1 and EP/P025285/1)the UKRI for his Future Leaders Fellowship(No.MR/T019123/1)。
文摘Realizing high work hardening and thus elevated strength–ductility synergy are prerequisites for the practical usage of body-centered-cubic high entropy alloys(BCC-HEAs).In this study,we report a novel dynamic strengthening mechanism,martensitic twinning transformation mechanism in a metastable refractory element-based BCC-HEA(TiZrHf)Ta(at.%)that can profoundly enhance the work hardening capability,leading to a large uniform ductility and high strength simultaneously.Different from conventional transformation induced plasticity(TRIP)and twinning induced plasticity(TWIP)strengthening mechanisms,the martensitic twinning transformation strengthening mechanism combines the best characteristics of both TRIP and TWIP strengthening mechanisms,which greatly alleviates the strengthductility trade-off that ubiquitously observed in BCC structural alloys.Microstructure characterization,carried out using X-ray diffraction(XRD)and electron back-scatter diffraction(EBSD)shows that,upon straining,α”(orthorhombic)martensite transformation,self-accommodation(SA)α”twinning and mechanicalα”twinning were activated sequentially.Transmission electron microscopy(TEM)analyses reveal that continuous twinning activation is inherited from nucleating mechanical{351}type I twins within SA“{351}”<■11>typeⅡtwinnedα”variants on{351}twinning plane by twinning transformation through simple shear,thereby accommodating the excessive plastic strain through the twinning shear while concurrently refining the grain structure.Consequently,consistent high work hardening rates of 2–12.5 GPa were achieved during the entire plastic deformation,leading to a high tensile strength of 1.3 GPa and uniform elongation of 24%.Alloy development guidelines for activating such martensitic twinning transformation strengthening mechanism were proposed,which could be important in developing new BCC-HEAs with optimal mechanical performance.
