Chemical randomness and the associated energy fluctuation are essential features of multi-principal ele-ment alloys(MPEAs).Due to these features,nanoscale stacking fault energy(SFE)fluctuation is a natural and indepen...Chemical randomness and the associated energy fluctuation are essential features of multi-principal ele-ment alloys(MPEAs).Due to these features,nanoscale stacking fault energy(SFE)fluctuation is a natural and independent contribution to strengthening MPEAs.However,existing models for conventional alloys(i.e.,alloys with one principal element)cannot be applied to MPEAs.The extreme values of SFEs required by such models are unknown for MPEAs,which need to calculate the nanoscale volume relevant to the SFE fluctuation.In the present work,we developed an analytic model to evaluate the strengthening ef-fect through the SFE fluctuation,profuse in MPEAs.The model has no adjustable parameters,and all parameters can be determined from experiments and ab initio calculations.This model explains available experimental observations and provides insightful guidance for designing new MPEAs based on the SFE fluctuation.It generally applies to MPEAs in random states and with chemical short-range order.展开更多
In this study,single-phase NbTiZr and NbTiZr(MoTa)_(0.1) medium-entropy alloys(MEAs)were investigated for their use in biomedical implants.The alloys were prepared by arc melting,and were then cold-rolled,annealed,and...In this study,single-phase NbTiZr and NbTiZr(MoTa)_(0.1) medium-entropy alloys(MEAs)were investigated for their use in biomedical implants.The alloys were prepared by arc melting,and were then cold-rolled,annealed,and characterized in terms of phase analysis,mechanical properties,fractography,and wear resistance.Both alloys showed a single body-centered cubic phase with superior mechanical,and tribological properties compared to commercially available biomedical alloys.Mo and Ta-containing MEAs showed higher tensile yield strength(1060±18 MPa)and higher tensile ductility(~20%),thus overcoming the strength-ductility trade-off with no signs of transformation-induced plasticity,twinning,or precipitation.The generalized stacking fault energy(GSFE)calculations on the{112}<111>slip system by the first-principles calculations based on density functional theory showed that the addition of less than0.2 molar fraction of Mo and Ta lowers the GSFE curves.This behavior posits the increase in ductility of the alloy by facilitating slips although strength is also increased by solid solution strengthening.The wear resistance of both alloys against hardened steel surfaces was superior to that of commercial biomedical alloys.Thus,we concluded that NbTiZr(MoTa)_(0.1)MEA with good tensile ductility is a potential candidate for biomedical implants.展开更多
基金sponsored by the U.S.Department of En-ergy,Office of Science,Basic Energy Sciences,Materials Science and Engineering Divisionsupported by the Office of Science of the U.S.Department of Energy under Contract No.DE-AC05-00OR22725+2 种基金the supports from(1)the National Science Foundation(DMR-1611180 and 1809640)with program directors,Drs.J.Yang,G.Shifletthe US Army Research Office(W911NF-13-1-0438 and W911NF-19-2-0049)with program managers,Drs.M.P.Bakas,S.N.Math-audhuthe support of U.S.Na-tional Science Foundation under grant DMR-1804320.
文摘Chemical randomness and the associated energy fluctuation are essential features of multi-principal ele-ment alloys(MPEAs).Due to these features,nanoscale stacking fault energy(SFE)fluctuation is a natural and independent contribution to strengthening MPEAs.However,existing models for conventional alloys(i.e.,alloys with one principal element)cannot be applied to MPEAs.The extreme values of SFEs required by such models are unknown for MPEAs,which need to calculate the nanoscale volume relevant to the SFE fluctuation.In the present work,we developed an analytic model to evaluate the strengthening ef-fect through the SFE fluctuation,profuse in MPEAs.The model has no adjustable parameters,and all parameters can be determined from experiments and ab initio calculations.This model explains available experimental observations and provides insightful guidance for designing new MPEAs based on the SFE fluctuation.It generally applies to MPEAs in random states and with chemical short-range order.
基金supported by the National Research Foundation of Korea(NRF-2020R1A5A6017701,NRF-2121R1A2C2014025)。
文摘In this study,single-phase NbTiZr and NbTiZr(MoTa)_(0.1) medium-entropy alloys(MEAs)were investigated for their use in biomedical implants.The alloys were prepared by arc melting,and were then cold-rolled,annealed,and characterized in terms of phase analysis,mechanical properties,fractography,and wear resistance.Both alloys showed a single body-centered cubic phase with superior mechanical,and tribological properties compared to commercially available biomedical alloys.Mo and Ta-containing MEAs showed higher tensile yield strength(1060±18 MPa)and higher tensile ductility(~20%),thus overcoming the strength-ductility trade-off with no signs of transformation-induced plasticity,twinning,or precipitation.The generalized stacking fault energy(GSFE)calculations on the{112}<111>slip system by the first-principles calculations based on density functional theory showed that the addition of less than0.2 molar fraction of Mo and Ta lowers the GSFE curves.This behavior posits the increase in ductility of the alloy by facilitating slips although strength is also increased by solid solution strengthening.The wear resistance of both alloys against hardened steel surfaces was superior to that of commercial biomedical alloys.Thus,we concluded that NbTiZr(MoTa)_(0.1)MEA with good tensile ductility is a potential candidate for biomedical implants.
