Plastic Deformation Behavior Of Co-based Co-8.8Al-9.8W Superalloy

Nickel-based superalloys are widely used in gas turbine engine components due to their excellent mechanical properties and corrosion resistance at high temperatures,and have long been regarded as important engineering materials.However,with the rapid development of aerospace engines,industrial gas turbines and nuclear power generation,nickel-based alloys can not meet the needs of some special fields.Compared with nickel-based superalloys,cobalt-based superalloys have attracted widespread attention from researchers due to their excellent high temperature corrosion resistance,heat fatigue resistance,weldability and higher working temperature.However,the traditional cobalt-based superalloys are mainly enhanced their high-temperature strength by solid solution strengthening and carbide dispersion strengthening.Compared with nickel-based superalloys strengthened by ordered??phase,their applications are limited due to their poor temperature bearing ability.Since the?/??coherent strengthening structure similar to nickel-based superalloys was found in the Co-Al-W ternary alloy in 2006,this new type of cobalt-based superalloy has been greatly favored by people,and is expected to replace nickel-based superalloys and become a new alloy system,but further improving the plastic deformation ability of new cobalt-based superalloy to make them have better mechanical properties is a problem that must be solved in expanding the field of alloy applications.Based on this,based on the related research done by our research group on Co-Al-W alloy,this paper mainly takes the Co-8.8Al-9.8W alloy as the basis to study its plastic deformation behavior at room temperature,and analyze its compression property and dislocation substructure under different compression deformation.The microstructure,microhardness,compression properties at room temperature,fracture morphology of Co-8.8Al-9.8W-x Ta?x=0,1,2,3,4,6,at%?alloy,and dislocation substructure under different compression deformation and the effect of strain rate on the properties and fracture morphology of Co-8.8Al-9.8W-2Ta alloy were analyzed by adding the element Ta.the main research conclusions are as follows:At room temperature,the as-cast microstructure of the Co-8.8Al-9.8W alloy is a dendritic structure,and no intergranular phase exists between the dendritic structures.After the addition of Ta element,the as-cast structure of each alloy is still a dendritic structure,and white intergranular phases exist between the dendrites,and the intergranular phase increases with the increase of Ta element.Phase analysis confirmed that the white intergranular phase was composed of?phase,Co₃Ta,and carbide CoCx.After the aging heat treatment,uniform and fine??strengthening phase precipitates on the?matrix of the alloy.After the addition of Ta element,with the increase of the content of Ta element,in addition to the precipitation of the??strengthening phase on each alloy matrix,cluster-like white substances also precipitated.The phase analysis confirmed that the white substance consisted of?phase,DO₁₉ phase,?phase and carbide CoCx.With the increase of the content of Ta element,the microhardness of the as-cast and aging heat-treated alloys showed an increasing trend.In addition,the microhardness of the as-cast alloy is obviously lower than that of the alloy after aging heat treatment due to the existence of solidification segregation and almost no precipitation of??strengthening phase.Under the room temperature compression test,all alloys have undergone certain plastic deformation and have similar stress-strain curve characteristics.Except for1Ta alloy,the yield strength?_0.2 of each alloy tends to increase with increasing Ta content,the maximum yield strength is 1 259 MPa,and the maximum compressive strength increases first and then decreases;the compressive pla sticity of each alloy?Except for 6Ta alloy?is better than that of the alloy without Ta element?0Ta?,and 2Ta alloy has the best plasticity.The fracture morphology of the alloy changes regularly,that is,from the initial cleavage fracture to the intergr anular and transgranular fracture.In addition,2Ta alloy is sensitive to strain rate.With the increase of strain rate,the stress-strain curve moves to the left,and the fracture mode of the alloy changes from cleavage fracture to cleavage and quasi-cleavage mixed fracture mode.Analysis of the dislocation substructure of Co-8.8Al-9.8W?0Ta?and 2Ta alloy after different amount of deformation under room temperature compression shows that the plastic deformation of 0Ta alloy is mainly through the continuous proliferation of dislocations in the?matrix phase,mutual entanglement and a small amount of dislocations entering in a bow-out manner and dislocations shearing??precipitated phase to complete.With the increase of the applied stress,the dislocation density increases continuously,and the distribution is almost uniform,and the alloy transforms from the initial nonuniform deformation to uniform deformation.Compared with the 0Ta alloy,the biggest difference of 2Ta alloy is that during plastic deformation,high-density stacking faults appearing in the?matrix channel and stack faults extending into the entire??precipitated phase,and some dislocations bypass and shear??precipitated phase,the deformation of sample is uniform.With the increase of the applied stress,the stacking faults on different{111}slip surfaces in the alloy are activated,and these stacking faults cross sli p with each other.That is to say,the plastic deformation of 2Ta alloy is mainly carried out by formi ng high-density stacking faults first,and subsequent dislocation shearing and dislocations bypassing the??precipitated phase.During the entire deformation process,the sample deformation is uniform.