Microstructure And Creep Behaviors Of A Re-free Single Crystal Ni-base Superalloy

A free-Re single crystal nickel based superalloys of the [001] orientation areprepared in the experiment. Under different heat treatment processes, compositionanalysis by SEM/EDS and test its creep properties in a creep machine, observe thestructure and test the creep performance of the single crystal nickel-based alloy，throughobservation of the microstructure, discuss the effect of solid solution on the organizationevolution and creep mechanism.Results show that, a larger degree segregation exist in the dendrite andinter-dendritic, thereinto, the elements which concentrate in the inter-dendritic is Ta, Al,Co, the enrichments which concentrate in the dendrite is Cr, Mo, W. After the increase ofsolution temperature, the degree of segregation further reduce between thedendrite/inter-dendrite, that increase the solid solution temperature has obvious effect onimprove the creep resistance of alloy. the creep activation of alloy calculate to be495.6kJ/mol under medium temperature/high stress, the creep activation of alloy calculate tobe476.3kJ/mol under high temperature/low stress.The main deformation mechanism of single crystal alloy is that dislocations slidingin the matrix and shear cubic phase during the medium temperature creep, among them,the super dislocations shear phase can decompose partial dislocation and stackingfaults. In the conditions of medium temperature/high stress, the primary and secondarysliping system alternating start, micro cracks produced in the boundary of the/phasesand extend along the direction of <110>, cause a creep rupture of the alloy eventually, itis the main fracture mechanism of the alloy in the medium temperature creep. It formsquare cleavage planes in the alloy during later creep, the main reason is that it producesthe large stress concentration near the port area during creep, can prompt the initiationand propagation of secondary crack along the {111} surface, the crack of (001) surfaceextended along <110> direction and connect with secondary cleavage face of {111}, tostop the initial crack extend along the (001) surface, which is the main reason of form the square cleavage planes.Under the condition of high temperature/low stress, the phase in the single crystalalloy start to form rafted structure at the beginning and and form N-type rafted structurevertical to stress axis, when the alloy come into the steady-state creep stage, the maindeformation mechanism is dislocation climbing. During the late creep, the maindeformation mechanism is dislocation shearing the rafted phase, during the creep, thedislocation alternate start, cause the initiation of crack and extend along the stress axis,until the alloy occurs rupture, that is the main fracture mechanism of the single crystalalloy during high temperature creep.