Method of developing a nickel-base superalloy

Abstract

The invention relates to a method of developing a nickel-base superalloy consisting of a γ-phase and γ′-phase for the production of single-crystal or directionally solidified bodies of material. The invention is characterized in that the properties of nickel-base superalloys with a volume proportion of γ′-phase of at least 50% after a degradation at room temperature are optimized, in that the composition of the alloy is chosen such that at room temperature a lattice displacement (δ) between the γ-phase and the γ′-phase is as high as possible. It is thereby attained that the yield strength at room temperature after degrading is comparatively high, and thus only a small difference of the yield strengths occurs between initial state and degraded state.

What is claimed is:  
     
         1 . A method of developing a nickel-base superalloy consisting of γ- and γ′-phases, for the production of single crystal or directionally solidified bodies of material, wherein the properties of nickel-base superalloys with a volume fraction of γ′-phase of at least 50% after degrading at room temperature are optimized, comprising: 
 selecting the composition of the alloy such that at room temperature a lattice displacement (δ) between the γ-phase and the γ′-phase is as high as possible, where 
 δ[%]=2( a   γ′   −a   γ )/( a   γ′   +a   γ ), 
 wherein a γ  is the lattice constant of the γ-phase, and wherein a γ′  is the lattice constant of the γ′-phase.  
 
     
     
         2 . A method according to  claim 1 , comprising: 
 determining the lattice constant (a γ ) of the γ-phase and the lattice constant (a γ′ ) of the γ′-phase according to the following equations:                      a   γ          [   Å   ]       =            3.524   +     0.0196                 Co     +     0.110                 Cr     +     0.478                 Mo     +     0.444                 W     +                            0.441                 Re     +     0.3125                 Ru     +     0.179                 Al     +     0.422                 Ti     +                              0.7                 Ta     +     0.7                 Nb       ,                             wherein the numbers before the element symbols give the relative atomic fraction of the respective element in the γ-phase; and                      a     γ   ′            [   Å   ]       =            3.57   -     0.004                 Cr     +     0.208                 Mo     +     0.194                 W     +     0.262                 Re     +                              0.1335                 Ru     +     0.258                 Ti     +     0.5                 Ta     +     0.46                 Nb       ,                             wherein the numbers before the element symbols give the relative atomic fraction of the respective element in the γ′-phase.    
     
     
         3 . A method according to  claim 1 , comprising: 
 characterizing the long term behavior of nickel-base superalloys including determining a degradation parameter (D) from the following equation:     D =( T −800) t   1/2 σ 1/5     wherein T=temperature in ° K, t=time in h, and σ=stress in MPa; and    determining the yield strength (σ 0.2 ) at room temperature after degrading is determined based on said degradation parameter (D).    
     
     
         4 . A method according to  claim 3 , comprising: 
 maximizing yield strength (σ 0.2 ) at room temperature.