Effect Of Single/dual Phase Micro-nano Particles On Microstructure And Mechanical Properties Of Ni-Fe-Cr-based Superalloys

Ni-Fe-Cr-based superalloys are widely applied in the aerospace and nuclear industries around the world due to their outstanding performance,which is subjected to complex working conditions.K4169 superalloys are typical representatives of Ni-Fe-Cr-based superalloys.To achieve high strength and plasticity of superalloy materials,it is generally necessary to obtain appropriate grain size microstructure uniformity and reduce alloy macro/micro defects.Fortunately,studies have shown that adding nucleants to superalloy melt like ceramic particles,which the grains can be refined by promoting nucleation,reducing microsegregation,and ultimately obtaining high-quality superalloy materials.However,the microstructure evolution and mechanical properties of casting and deformed superalloys by adding ceramic particles with different contents and different ways of adding ceramic particles,especially Ti C and Ti C-Ti B₂ particles,are rarely reported.Therefore,this paper took 4169 superalloys as the research object.Ti C-Ti B₂/4169and Ti C/4169 superalloys were successfully prepared by adding Ti C-Ti B₂/Al and Ti C/Al master alloys to the melt.In this paper,a suitable master alloy addition process is confirmed;The effects of different content Ti C-Ti B₂ particles on the microstructure evolution and mechanical properties of cast 4169 superalloy were studied.The effects of Ti C-Ti B₂ particles and Ti C particles on the precipitated phase and mechanical properties of 4169 superalloys in different states were compared.As for cold rolling deformation,Ti C nanoparticles are introduced to refine the grains,promote the dissolution of the Laves phase during the homogenization process and reduce microsegregation.It can promote the transformation of the morphology of theδphase during the heat treatment process,thereby regulating the grain size after recrystallization and improving the mechanical properties of 4169 superalloys.The main conclusions of this paper are as follows:（1）Among the three additive processes of master alloys,by extending the holding time-scheme B:"melt the bar superalloy material,add the corresponding mass fraction from the top of the crucible after the alloy is melted,and mechanically crush the powdered master alloys,keep the heat for 10min and start pouring,pour into the graphite mold,the pouring temperature is 1500℃".The grain refinement trend and microsegregation of the corresponding alloys are the most obvious,and the room temperature and high-temperature tensile properties are excellent.（2）The grains size of cast 4169 superalloy was refined with the increase of Ti C-Ti B₂ particles content,but the cast microsegregation increased with the increase of particles content;When the particles content of Ti C-Ti B₂ increased to 0.3wt.%and above,the Laves phase morphology was changed and eutectic boride was precipitated from the grain boundary and interdendritic eutectic regions,which reduced the plasticity of the superalloys.After adding the same content of Ti C and Ti C-Ti B₂particles in the 4169 superalloy,Ti C particles hardly change the type and morphology of the second phase in theγmatrix,and the effect of refinement grains is more significant.On the contrary,the Ti C-Ti B₂ particles will promote the precipitation of a large number of brittle hard lamellar eutectic borides in interdendritic eutectic regions of the superalloy,retard the precipitation of the Laves phase,and the Laves phase changes from island to block or skeleton.In terms of mechanical properties,regardless of room temperature or high temperature tensile,Ti C-Ti B₂ particles make the alloy show higher yield strength,but the elongation is seriously damaged.However,the Ti C particles maintain good plasticity while improving the strength of the alloy.（3）Ti C Nanoparticles promoted the grain refinement of 4169 superalloy and transformed the columnar grains to equiaxed grains;The dendrite arm is further coarsened,and the interdendritic eutectic regions are narrowed to reduce microsegregation.During the homogenization process,the eutectic Laves phase dissolution in the interdendritic eutectic regions was accelerated.（4）Ti C particles control the grain size and precipitated phase morphology of cold-rolled 55%+solution heat treatment 4169 superalloy.After the addition of Ti C nanoparticles,the grain size increased slightly,which promoted the transition from the needle-likeδphase to the short rod/granularδphase;Theδphase is reduced,refined,and distributed more uniformly.Cold rolling 66%+solution treatment,δphase precipitation increased with the increase of cold rolling degree.（5）After standard heat treatment（SHT）,most of theδphases of 4169 superalloy without Ti C nanoparticles were precipitated in the form of long needles;Most of theδphases of 4169 alloy containing Ti C nanoparticles were precipitated in short rod or granular and the density of theγ’andγ’phases is larger and smaller.（6）Ti C nanoparticles improve the strength and plasticity of the 4169 superalloy.In the results of high-temperature tensile experiments,0.1Ti C/4169 superalloy improved its plasticity while maintaining strength.