Effect Of Ta Content On Microstructure And Mechanical Properties Of FGH4098

In this paper,the difference of microstructure and precipitated phase of FGH4098with different contents of Ta,which were 0,1.2%,2.4%,3.5%and 4.7%（mass fraction）,was studied through OM,SEM,FE-SEM,EDS,EPMA,TEM and XRD,combined with thermo-dynamic calculation.Mechanical properties at room temperature and elevated temperature of heat-treated FGH4098 with different Ta content were also tested.The influence of Ta content on theγ′phase,MC carbide and precipitation behavior of TCP phase during long-term aging,were investigated in detail.The relation between mechanical properties and microstructure was analyzed.At the same time,the optimal Ta content of FGH4098 were attained.The main significance of this paper is helping to have a deeper understanding of the influence of Ta on the third generation P/M superalloy.The results shows that,Ta mainly formsγ′phase,in which Ta can increase the content ofγ′phase,increase the size of secondaryγ′phase and promote the morphologic change of secondaryγ′phase from ellipsoidal to squarish,make the Ni₃（Al,Ti,Nb）transform to Ni₃（Al,Ti,Ta,Nb）and promote the process of growth and division of secondaryγ′phase during long-term aging.Part of Ta may form MC carbide,make the（Ti,Nb）C transform to（Ta,Ti,Nb）C,decline the distribution of MC carbide along PPB,and promote uniform distribution of MC carbide in the alloys.Ta can also keep the structure stability of MC carbide at elevated temperature.During long-term aging at 650℃⁸00℃,σphase may precipitate.The increase of Ta content can increase the precipitation tendency ofσphase at elevated temperature.Basing on the strength effect ofγ′phase and MC carbide,with the increasing of Ta content,the tensile strength of alloys improves minimally.Adding moderate content of Ta can obviously improve the stress rupture property and decline 650℃fatigue crack growth rate.Excessive content of Ta will significantly reduce stress rupture properties of alloys at elevated temperature,due toσphase precipitating at high temperature.Considering all the effect mentioned above,FGH4098 with about 1.2%².4%Ta has the optimal performance.