The Effect Of TiC Nanoparticles On Microstructure And Properties Of Cast Superalloy

Precipitation-strengthened cast superalloy is widely used in aerospace,energy and other fields due to their low production cost,simple manufacturing process and excellent mechanical properties at medium and low temperature.With the rapid development of these fields,higher requirements are put forward for the performance of high-temperature structures,which requires that the micro structure and properties of superalloy need to be further improved.Grain refinement can effectively improve the strength,ductility,durability and fatigue properties of cast superalloy.Adding refiners is a common way to refine grains,among which nitrides(TiN)and intermetallics(Co3FeNb2,CrFeNb)are more effective.The addition of refiners can reduce the grain size and improve the strength plasticity,fatigue life,stress-rupture strength and life of the superalloyHowever,the mechanism of grain refinement affecting the micro structure(such as dendrite structure)and strengthening phases(such as ?' phase and carbide)of precipitation-strengthened cast superalloy has not been reported.In addition,there are few studies on minor TiC ceramic nanoparticles as the refiner of superalloy.Therefore,in this paper,minor amount of TiC nanoparticles were added to K214 and K465 precipitation-strengthened cast superalloy by the method of TiC/Al master alloy.The effect of TiC ceramic nanoparticles on the micro structure and properties of precipitation-strengthened cast superalloy was studied.The relationship between TiC ceramic nanoparticles,grain refinement,microsegregation,?' phases,carbides and mechanical properties was explored.The main conclusions are as follows:(1)TiC nanoparticles reduced the grain size of cast superalloy by 30%-60%,and the effect of grain refinement was obvious(2)After adding TiC nanoparticles,the secondary dendrite arm spacing of as-cast K214 superalloy increased by 9?m,the area fraction of interdendritic segregation decreased relatively,the microsegregation and the size of ?' phases decreased.TiC weakened the cross-shaped morphology of the dendrite of K465 superalloy,and the dendrite morphology began to become irregular.The morphology of MC-type carbides in K465 superalloy changed,from Chinese character to block(3)After adding TiC nanoparticles,the ultimate tensile strength of K214 superalloy improved with unchanged ductility.The tensile results at room temperature showed that the ultimate tensile strength of the as-cast superalloy increased by 82 MPa;The ultimate tensile strength of heat-treated superalloy increased by 103 MPa.The tensile results at 900? showed that the ultimate tensile strength of the as-cast superalloy increased by 35 MPa;The ultimate tensile strength of the heat-treated superalloy increased by 60 MPa(4)After adding TiC nanoparticles,the uniform elongation of K465 as-cast bottom specimen significantly improved with unchanged ultimate tensile strength.The tensile results at room temperature showed that the addition of 0.02wt.%TiC decreased the yield strength of as-cast superalloy by about 60MPa and increased the uniform elongation by 224%;The addition of 0.1wt.%TiC decreased the yield strength of as-cast superalloy by about 49MPa and increased the uniform elongation by 72%;The addition of 0.02wt.%TiC increased the break elongation of heat-treated superalloy by 120%;The addition of 0.1wt.%TiC had no effect on the break elongation of heat-treated superalloy.