Microstructure And High Temperature Creep Properties Of A Containing Re/Ru Single Crystal Nickel-based Superalloy

By means of heat treatment at different regimes, microstructure observation andSEM/EDS composition analysis, the influence of heat treatment on the segregation extent ofthe elements in the inter-dendrite/dendrite regions of the containing Re/Ru single crystalnickel-based superalloy is investigated. By means of creep properties measurement andmicrostructure observation under SEM and TEM, the influence of heat treatment on themicrostructure and creep behaviors of the Re/Ru single crystal nickel-based superalloy isinvestigated.The results show that the elements Cr, Re, W and Mo are enriched in the dendriteregions in the as-cast alloy, the elements Al, Ta, Ru and Co are enriched in the inter-dendriteregions. Wherein, the element Re displays the strongest negative segregation feature, whilethe element Ta displays the strongest positive segregation feature. As the solutiontemperature enhances, the segregation extent of the elements in the inter-dendrite/dendriteregions of the alloy is obviously reduced, which may improve the homogenization extent ofthe elements in the alloy. In the temperature ranges of1040℃~1115℃, the containingRe/Ru single crystal nickel-based superalloy displays a better creep resistance and longercreep lifetime. In the ranges of1085℃~1115℃and1040℃~1070℃, the activationenergies of the alloy during steady state creep are measured to be Q=493.7kJ/mol and Q=504.7kJ/mol, respectively. In the initial stage of creep at high temperature, the cubical phase in alloy has transformed into the N-rafted structure along the direction perpendicularto the stress axis. The deformation mechanism of the alloy during steady state creep isdislocation slipping in the matrix channels and shearing into the rafted phase, while theone of alloy in the later stage of creep is dislocations slipping in the matrix and shearinginto the rafted phase. During creep, significant amount of fine cubical phase areprecipitated in the matrix channels between the rafted phase. And the fine cubical phase is gradually grown up as the creep goes on, which may hinder the movement ofdislocation in the matrix to improve effectively the creep resistance of alloy at hightemperature.Moreover, the adding element Ru decreases the stacking fault energy of alloy, so thatthe dislocations shearing into the rafted phase during creep at high temperature may isdecomposed to form the configuration of the partial dislocations plus APB, which can inhibit the cross slip of dislocations. These are thought to be the main reason of the alloy having thebetter creep resistance at high temperature. In the later stage of creep, the alternate slippingof significant amount of dislocations results in the twisted of the rafted phase to promotesome cavities appearing in the interfaces of the rafted phase with twisted feature. As thecreep goes on, the large number cavities are congregated in the interfaces of the rafted/phases to form the micro-crack, and the micro-cracks are propagated, as the creep goeson, up to the occurrence of creep fracture, which is thought to be the fracture mechanism ofthe alloy during creep at high temperature.