Cluster-plus-glue-atom Composition Formulas For Nickel-based Superalloys

With the cluster-plus-glue-atom model,this paper puts forward the composition formula of nickel-based superalloys,analyzes available compositions,probes performance,experimental tests and predicts performance.First,this paper discovers composition rule and development tendency,presents the ideal model with corresponding composition formula for nickel-based single crystal superalloys by analyzing composition.Secondly,in virtue of composition formula of nickel-based superalloys,both the kinds and the number are clearly for bonds.Meanwhile,this paper also built the relationship between composition formula and temperature capability with bond strength being measured by condensed bond enthalpy.At the same time,this paper also built the relationship between composition formula and temperature capability with bond strength being measured by condensed bond enthalpy.Temperature capability are predict by the composition formula.At last,the first generation single crystal superalloys have been validated by experiments about the ideal model.Compared to the first generation single crystal superalloys,the creep rupture life at 1000 ?/219 MPa are at the average level and the incipient melting temperature are at higher level for design superalloys.Specifically,this paper covers the following three aspects:(1)According to the enthalpy of mixture with the based nickel solvent,the alloying elements are classified into four groups:1 Ni-like(Ni:Ni,Co,Fe,Re,Ru and Ir)elements,weaker enthalpy of mixture with Ni,ranging between-2?-+2 kJ/mol;2 y-forming Cr-like(Cr?:Cr,Mo and W)elements,enthalpy of mixture with Ni ranging between-7?-3 kJ/mol;3?'-forming Cr-like(Cr?':Ti,Ta,Nb and V)elements,enthalpy of mixture with Ni ranging between-35?-18 kJ/mol;4 larger negative enthalpy of mixture with Ni,Al,-22 kJ/mol.As a result of alloying elements classification,compositions of 272 available nickel-based superalloys fall within narrow composition ranges(Ni,60 at.%?80at.%;glue atoms,2?7).Adding y'-forming elements(Al,Cr?')into Ni-Cr? alloys is the development progress of nickel based superalloys.Especially,the formula of directionally solidified and single crystal superalloys evolutes along a composition line[(Al,Cr ?'),-Ni,2](Al,Cr?')1.5Cr?x-1.5).For the high generation single crystal superalloys,the compositions finally converge towards to the ideal model,[(Al,Cr?')1-Ni12](Al,Cr?')1.5Cr?1.5=Ni75Al12.5Crv?9.375Cr?'3.125 at.%,and the ideal model conforms to the Fried el Oscillation and cluster-resonance model.Alloying elements classification also predicts volume fraction of ?'.(2)Because of the composition formula of nickel based superalloys,both the kinds of bonds and the number of bonds are clearly.For face-centered-cubic solid solution,every atom has 6 own bonds resulting from the coordinate number being 12.As a result,every composition formula with x glue atoms has 6×(13+x)bonds,containing 12 Center-Shell bonds,12x Glue-Shell bonds and(66-6x)Shell-Shell bonds.Bond strength being measured by condensed bond enthalpy,this paper discovers that the average bond enthalpy and the weak bond enthalpy can reflect temperature capability and creep rupture life respectively.The composition formula is also moving towards the ideal composition formula[Al-Ni12]Al1Cr?'0.5?Cr?1.5.for high generation single crystal superalloys with higher temperature capability and longer creep rupture life.(3)With the ideal model of nickel-based superalloys([Al-Ni12]Al1Cr?'0.5Cr?1.5),on the basis of the 1st generation single crystal superalloys DD407(AM3)which are used in the aero-engine of the helicopter,this paper raises three Group Cluster Superalloys:Group A,[Al-Ni11Co1](Al1TaxTi0.5-xCr1Mo0.25W0.25),x=0,0.25 and 0.5(the corresponding mass fractions of Ta and Ti are respectively 0Ta-2.65Ti,4.82Ta-1.28Ti and 9.32Ta-0Ti);Group B,[Al-Ni12-yCoy](Al1Ti0.25Ta0.25Cr1Mo0.25W0.25),y=1.5,1.75,2 and 2.5(the corresponding mass fractions of Co are respectively 9.43Co,11Co,12.57Co and 15.71Co);Group C,[Al-Ni12xCox](Al1Ta0.25Ti0.25Cr1Mo0.25W0.25),z=1.25,2,2.5 and 3,[Al-Ni11Co1]Al1Ti0.5Cr1 Mo0.25W0.25),(the corresponding mass fractions of Co,Ta and Ti are respectively 7.86Co,12.57Co,15.71Co,18.86Co and 0Ta-2.65Ti).Compared to DD407(46h),both 7.86 Co and 12.75 Co alloys have longer creep rupture life at 1000 ?/219 Mpa which is in the average level of first generation single crystal superalloys.Meanwhile,all the incipient melting temperatures of Cluster Superalloys,at higher level of first generation single crytstal superalloys,are higher than that of Nasair 100(1330 ?).For Group A,with increasing Ta(decreasing Ti),the ?'/? lattice negative misfits ? shrinks from-0.262%to-0.247%.Although reduced,the lattice negative misfits ?,maintaining at 900 ? long-term aging,reduce coarsening rate.Meanwhile,creep rupture life at 1050 ?/120 MPa are increasing with increasing Ta(decreasing Ti)for Group A.For Group B,the addition of Co does not increase the coarsening rate and the coarsening rate is of the same order of magnitudes(10-5 ?m3/h)with the third generation single crystal superalloys.Moreover,Co is able to cripple atomic interaction(enthalpy of mixture and bond enthalpy),resulting in reducing creep rupture life at 1050 ?/120 MPa.Furthermore,after creep at 1050 ?/120 MPa,the coarsening of y' is N-type raft for Group A and B.For Group C,the bond enthalpy is also able to reflect the creep rupture life tendency.For Group C,this paper also finds N-type raft at 1100 ?/137 MPa and 1000 ?/219 MPa,but no No raft at 760 ?/780 MPa.At the same time,both 7.86Co and 12.57 Co have longer creep rupture life at 1000 ?/219 MPa than that of DD407(46h).The obvious congruent relationship between temperature capability and average bond enthalpy are discovered,TTC(K)=-4071.852×Iave-1867.180,Iave is average bond enthalpy(eV/bond).The average bond enthalpy is able to predict temperature capability.The composition formula is able to design new nickel-based superalloys effectively.