Dynamics of grain boundary premelting (original) (raw)

The mechanical strength of a polycrystalline material can be drastically weakened by a phenomenon known as grain boundary (GB) premelting that takes place, owing to the so-called disjoining potential, when the dry GB free energy \sigma _{gb}σgbexceedstwicethefreeenergyofthesolid–liquidinterfaceσ gb exceeds twice the free energy of the solid–liquid interfaceσgbexceedstwicethefreeenergyofthesolid–liquidinterface\sigma _{sl}σsl.WhilepreviousstudiesofGBpremeltingarealllimitedtoequilibriumconditions,weuseamulti−phasefieldmodeltoanalyzepremeltingdynamicsbysimulatingthesteady−stategrowthofaliquidlayeralongadryGBinaninsulatedchannelandtheevolutionofapre−meltedpolycrystallinemicrostructure.Inbothcases,ourresultsrevealthecrucialinfluenceofthedisjoiningpotential.AdryGBtransformsintoapre−meltedstateforagrain−size−dependenttemperatureintervalaroundσ sl . While previous studies of GB premelting are all limited to equilibrium conditions, we use a multi-phase field model to analyze premelting dynamics by simulating the steady-state growth of a liquid layer along a dry GB in an insulated channel and the evolution of a pre-melted polycrystalline microstructure. In both cases, our results reveal the crucial influence of the disjoining potential. A dry GB transforms into a pre-melted state for a grain-size-dependent temperature interval aroundσsl.WhilepreviousstudiesofGBpremeltingarealllimitedtoequilibriumconditions,weuseamulti−phasefieldmodeltoanalyzepremeltingdynamicsbysimulatingthesteady−stategrowthofaliquidlayeralongadryGBinaninsulatedchannelandtheevolutionofapre−meltedpolycrystallinemicrostructure.Inbothcases,ourresultsrevealthecrucialinfluenceofthedisjoiningpotential.AdryGBtransformsintoapre−meltedstateforagrain−size−dependenttemperatureintervalaroundT_mTm,suchthatacriticaloverheatingofthedryGBsoverT m , such that a critical overheating of the dry GBs overTm,suchthatacriticaloverheatingofthedryGBsoverT_m$$ T m should be exceeded for the classical melting process to take place, the liquid layer to ach...