The highly thermal stability precipitates strengthen creep resistance for alloys,which require precipitates to resist coarsen at elevated temperature.In the Mg-RE-Zn(Ag)series alloys,the key strengthening phase-γ&quo...The highly thermal stability precipitates strengthen creep resistance for alloys,which require precipitates to resist coarsen at elevated temperature.In the Mg-RE-Zn(Ag)series alloys,the key strengthening phase-γ"phase,remains its single-unit-cell height throughout aging process.The origin of such extremely thermal stability ofγ"phase is still unclear.By using the first-principles calculations,it is found that the formation ofγ"phase introduces compressive strain to its surroundingα-Mg lattice and simultaneously alter charge distribution ofα-Mg lattice near theα-Mg/γ"hetero-interface.These two variations overα-Mg lattice lead to lower vacancy formation energies and migration energy barriers for solute atoms near theα-Mg/γ"hetero-interface in comparison with that of bulk condition.Consequently,the variations facilitate rapid diffusion of solute atoms near theγ"phase and promote nucleation rate of otherγ"plates around it.On the basis of ledge-thickening model,the origin of nucleation/growth ofγ"phase with single-unit-cell height was explained.Thermodynamically and kinetically,the solute atoms are not apt to migrate into the nearest basal plane adjacent to theγ"phase.Moreover,the lower aging temperature(~200℃)and almost completely coherentα-Mg/γ"hetero-interface lead to the ledges are extremely hard to nucleate on the hetero-interface.Therefore,γ"plates maintain single-unit-cell height throughout aging process.展开更多
基金This work was financially supported by the National Key Research and Development Program of China(No.2016YFB0701202)the Fundamental Research Funds for the Central Universities(Nos.N2007011,N160208001)111Project(No.B20029)。
文摘The highly thermal stability precipitates strengthen creep resistance for alloys,which require precipitates to resist coarsen at elevated temperature.In the Mg-RE-Zn(Ag)series alloys,the key strengthening phase-γ"phase,remains its single-unit-cell height throughout aging process.The origin of such extremely thermal stability ofγ"phase is still unclear.By using the first-principles calculations,it is found that the formation ofγ"phase introduces compressive strain to its surroundingα-Mg lattice and simultaneously alter charge distribution ofα-Mg lattice near theα-Mg/γ"hetero-interface.These two variations overα-Mg lattice lead to lower vacancy formation energies and migration energy barriers for solute atoms near theα-Mg/γ"hetero-interface in comparison with that of bulk condition.Consequently,the variations facilitate rapid diffusion of solute atoms near theγ"phase and promote nucleation rate of otherγ"plates around it.On the basis of ledge-thickening model,the origin of nucleation/growth ofγ"phase with single-unit-cell height was explained.Thermodynamically and kinetically,the solute atoms are not apt to migrate into the nearest basal plane adjacent to theγ"phase.Moreover,the lower aging temperature(~200℃)and almost completely coherentα-Mg/γ"hetero-interface lead to the ledges are extremely hard to nucleate on the hetero-interface.Therefore,γ"plates maintain single-unit-cell height throughout aging process.
