Creep Behaviors And Effecting Factors Of Re/Ru Containing Nickel- Based Single Crystal Superalloys

By means of designing and preparing the 4.5%Re-containing and 4.5%Re/3.0%Ru-containing nickel-base single crystal superalloys,the concentration distribution of the elements in the dendritic/inter-dendritic and?/?'phases of the as-cast and heat treated alloys are measured to investigate the influences of Re,Ru on the elements segregation and distribution behaviors.By means of measuring the creep properties of 4.5%Re and 4.5%Re/3.0%Ru superalloys under different conditions,the microstructures observation,contrast analysis of dislocation configurations and measuring the concentrations distribution of elements in?/?'phases,the influences of Ru on the creep behaviors and elements distribution of the Re-containing superalloy are investigated.By means of calculating the stacking fault energies of alloys at various temperatures by thermodynamics and TEM methods,combining with the microstructure observations,the influence of stacking fault energy on the deformation mechanism of the alloys during creep is investigated.Results show that the element Re is strongly segregated in the dendritic regions to promote the nucleation of dendrite,which may increase the dendrite quantity of as-cast Re-containing superalloys.During solidification,the elements with higher melting point are firstly solidified to repel the elements Ni and Al with lower melting point,so that the concentrations of Ni and Al in inter-dendritic region is increased,which is thought to be the main reason of much more eutectic structures with bigr size appearing in the inter-dendritic region of as-cast 4.5%Re alloy.The element Ru is mainly enriched in the inter-dendritic region,and the one may decrease the precipitation temperature of?'phase,which increases the segregation extents of Al and Ta in dendrite region to enhance the segregaton extents of other elements in the dendritic/inter-denrite regions.After fully heat treated,the Ru atoms in alloy may occupy the lattice location of Al in Ni₃Al phase,which is thought to be the main reason of the concentrations distribution of Al,Ta and Ru in?'phase appearing the complementary relation.The Ru atoms have a stronger binding forces with the W,Mo and Re atoms,which may make the more W,Mo and Re atoms to dissole in?'phase to enhance the partitioning ratios of elements in?'/?phases and improve the creep resistance of the alloy.After adding 3.0%Ru into 4.5%Re alloy,the creep life of the alloy at 800?/800MPa is increased from 273h to 323h.The deformation mechanism of the alloy during creep at temperature near 800?is dislocations slipping in?matrix and shearing into the cubic?'phase.Wherein,the dislocations shearing into?'may be both decomposed on{111}plane to form the?a/3?<112>partials plus super-lattice intrinsic stacking fault?SISF?and cross-slipped from{111}plane to{100}plane to form the configuration of K-W locks plus antiphase domain boundary?APB?,which may hinder the slipping and cross-slipping of dislocations to improve the creep resistance of alloy.During steady stage of creep at temperature nore than 980?,the deformation mechanism of the alloy is dislocations slipping in?matrix and climbing over the rafted?'phase.In the later stage of creep,the dislocations shearing into the rafted?'phase may form the configuration of K-W locks or K-W locks plus APB.During creep of 4.5%Re/3.0%Ru alloy at 980?,the dislocations shearing into the rafted?'phase may be decomposed on{111}plane to form the partials plus SISF,which is thought to be the main reason of the alloy having a better creep resistance.After adding 3.0%Ru into 4.5%Re alloy,the creep life of the alloy at 1100?/137MPa is increased from 164h to 321h.The deformation mechanism of the alloy in the later stage of creep is dislocations slipping in?matrix and shearing into the rafted?'phase.And the dislocations in?'phase may be cross-slipped from{111}to{100}plane to form K-W locks.Wherein,the more K-W locks retained in the alloy during creep is thought to be the main reason of the alloy having a better creep resistance at high temperature.The stacking fault energies of 4.5%Re and 4.5%Re/3.0%Ru alloys increase with the temperature,wherein,the Ru atoms may decrease the free energies??G_s?of the atomic segregation to make easily the atoms to be congregated,which is thought to be the main cause of increasing smaller extent of the stacking fault energies of the alloy with enhancing temperature.When the stacking fault energy of the alloy is lower than 200mJ/m^-2,the dislocations shearing into the rafted?'phase may be decomposed on{111}plane to form the configuration of Shockley partials plus SISFs.When the stacking fault energy of the alloy is close to 200mJ/m^-2,the dislocations shearing into the rafted?'phase may be decomposed on{100}plane to form the configuration of K-W locks plus APBs and some dislocations may be decomposed on{111}plane to form the Shockley partials plus SISFs.As the stacking fault energy increases further,the dislocations in the rafted?'phase can not be decomposed.