The early precipitation ofγ’-Co3(Al,W)phase affects the spatial distribution and kinetic evolution of precipitates for the morphology transmission effect,but the nucleation and concomitant growth are not studied sti...The early precipitation ofγ’-Co3(Al,W)phase affects the spatial distribution and kinetic evolution of precipitates for the morphology transmission effect,but the nucleation and concomitant growth are not studied still by aging experiments due to the expeditious precipitation ofγ’phase in Co-Al-W alloy.By using the phase-field simulation with sublattice free energy,the early-stage kinetics evolution ofγ’-Co3(Al,W)phase in a medium supersaturation Co-9 Al-8 W(at.%)alloy aged from 1023 K to 1173 K is investigated.The influences of aging temperature on the evolution of morphology and composition ofγ’phase,and the kinetics of nucleation and growth to coarsening are clarified.It is found that the rates of composition evolution of W inγphase are two or three times that ofγ’phase,and the W compositions inγandγ’phases show a linear relationship with time t–1/3,which means that the coarsening takes place earlier at high temperature.In addition,the equilibrium partitioning ratios indicate Al and W partition into theγ’phase and the ratios decrease with elevated temperature.The compositional variations across theγ/γ’phase interfaces suggest that low aging temperature makes the stoichiometric ratio closer to 3:1.Moreover,the precipitation evolutions from early nucleation to growth and coarsening in Co-Al-W alloy are distinguished,and the rate constants of square and cube of average particles radius increase with temperature.In later growth stage,the relationship of the square of average particles radius and time is obeyed,while the steady-state coarsening stage follows the cube law.The time exponents of particles number density at the coarsening stage are close to–1 of Kuehmann-Voorhees(KV)theory.The study demonstrates that the early-stage evolution ofγ’phase which is undiscovered in the experiment can be captured by the phase-field simulation,and the resultant kinetics laws agree well with the experimental and theoretical results.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51571122)the Fundamental Research Funds for the Central Universities(No.30916015107)。
文摘The early precipitation ofγ’-Co3(Al,W)phase affects the spatial distribution and kinetic evolution of precipitates for the morphology transmission effect,but the nucleation and concomitant growth are not studied still by aging experiments due to the expeditious precipitation ofγ’phase in Co-Al-W alloy.By using the phase-field simulation with sublattice free energy,the early-stage kinetics evolution ofγ’-Co3(Al,W)phase in a medium supersaturation Co-9 Al-8 W(at.%)alloy aged from 1023 K to 1173 K is investigated.The influences of aging temperature on the evolution of morphology and composition ofγ’phase,and the kinetics of nucleation and growth to coarsening are clarified.It is found that the rates of composition evolution of W inγphase are two or three times that ofγ’phase,and the W compositions inγandγ’phases show a linear relationship with time t–1/3,which means that the coarsening takes place earlier at high temperature.In addition,the equilibrium partitioning ratios indicate Al and W partition into theγ’phase and the ratios decrease with elevated temperature.The compositional variations across theγ/γ’phase interfaces suggest that low aging temperature makes the stoichiometric ratio closer to 3:1.Moreover,the precipitation evolutions from early nucleation to growth and coarsening in Co-Al-W alloy are distinguished,and the rate constants of square and cube of average particles radius increase with temperature.In later growth stage,the relationship of the square of average particles radius and time is obeyed,while the steady-state coarsening stage follows the cube law.The time exponents of particles number density at the coarsening stage are close to–1 of Kuehmann-Voorhees(KV)theory.The study demonstrates that the early-stage evolution ofγ’phase which is undiscovered in the experiment can be captured by the phase-field simulation,and the resultant kinetics laws agree well with the experimental and theoretical results.
