Dissolution Kinetics Evolution And Microstructure Of Precipitates In Ni-Al Alloys

High temperature stability of the L1₂???phase is the main factor to determine the properties of nickel-based superalloy.However,the??phase will dissolve under high temperature,and stress can influence the properties of nickel-based superalloys.Therefore,it has great significance for the investigation of??phase morphology and kinetics evolution under high temperature and stress.In this paper,??phase morphology and kinetics evolution under external strain with different aging methods are studied by sub-lattice free energy phase field model in two dimensional simulation system,which can provide theoretical reference for the high temperature stability of nickel-based superalloys.The arrangement of??phase has influence on its high temperature stability.Ni?15 at.%Al alloy in the process of isothermal aging at 700 K,??phase along the elasticity soft direction[01]or[10]can be combined with the adjacent??phase particles in the same queue,the rest of the??phase tend to dissolve through the Oswald ripening.Moreover,during the process of continuous heating,the??phase in the queue dissolve slower,showing the better high temperature stability.In process of continuous heating,coarsening and dissolving of??phase in Ni?15 at.%Al alloy happen at the same time.With the lower heating rate,the??phase volume fraction and average radius increase in the early stage of heating process,which is the"re-dissolution lag"phenomenon.Along with heating rate increasing,"re-dissolution lag"phenomenon gradually weakens.Uuantitative analysis shows that,in the process of continuous heating,??phase volume fraction and particle average radius have power function relation with the heating rate k(f=ak^b+c).In isothermal aging process of Ni?17 at.%Al alloy,the external strain(?)contributes to the elastic strain energy difference between the horizontal and vertical matrix channels,bringing the directional diffusion of Al atoms as well as rafting morphology of??phase.Moreover,the external stress leads to the change of phase equilibrium,the volume fraction of??phase increase by 1.07%when the?=0.02.In the process of continuous heating of Ni?17 at.%Al alloy,the heating rate affects the dissolution of??phase,with the increasing heating rate,dissolution rate of??phase increases.The external strain makes the adjacent??phase combine,which reduces the??phase specific surface area,therefore the??phase dissolves even more slowly.Tensile strain inhibites the diffusion of Al atom,slows down the dissolution of??phase,and narrows the?/??phase interface width(?);whereas,the compressive strain promotes the Al atom diffusion,accelerates the dissolution of??phase,and widens the?/??phase interface width(?).Among the factors influencing??phase dissolution,heating rate outweighs the reducing of??phase specific surface area and Al atom diffusion influenced by the external strain.