First-principles Study On The Occupation Behavior Of Cr And Oxygen In Ni-Ni₃A1 System And Oxygen With Misfit

Though it is well known that Cr can improve the oxidation resistance of Ni-Ni3 Al superalloy, the mechanism of the oxidation resistance of Cr in superalloy is not clear, yet. First-principle calculation method is applied here to study the occupation behavior of Cr and its influence on the occupancy behavior of O in Ni-Ni3 Al system with lattice misfit, exploring the mechanism of the oxidation resistance of Cr in Ni-Ni3 Al alloys system. It is found that:(1) The analyses of the binding energies and substitute energies of system with and without Cr show that lattice misfit will do harm to the stability of Ni-Ni3 Al alloy system during the investigated lattice misfit(-8%, 7%).(2) The binding energies and substitute energies of system increase in the order as follow: iCr1 ? iCr2 < iCr3 ? iCr4 < iCr0, indicating that Cr itself can stay stably in any phase of Ni-Ni3 Al system and Cr especially the Cr in the Ni phase can increase the stability of Ni-Ni3 Al alloy system.(3) When both Ni phase phases and Ni3 Al phase exist simultaneously, Cr firstly prefers Ni phase rather than Ni3 Al phase, which makes Cr in Ni-Ni3 Al alloy system have little chance to occupy Al sublattice in Ni3 Al phase. In Ni3 Al phase, the site preferring of Cr is Al sublattice not Ni sublattice. This phase preferring of Cr to Ni phase and the site preferring of Cr to Ni sublattice are not influenced by lattice misfit.(4) BO analysis of the Ni-Ni3 Al system without Cr shows that the int2?/ E at Al sublattices are obviously smaller than those at Ni sublattices in both Ni phase and Ni3 Al phase, and the corresponding modes theint2?/ E to lattice misfit at Al sublattices are opposite to those at Ni sublattices in both Ni phase and Ni3 Al phase, which may be the internal cause of brittleness of Ni-Ni3 Al system and Ni3 Al alloys.(5) BO analysis of the Ni-Ni3 Al system with Cr shows that Cr decreases the degreeoftheanisotropybetweennisublatticeandalsublatticefromtworespects:oneistoincreasethevalueofint2?/eatalsublatticetobeclosetothatatnisublattice,andtheotheristoreversethecorrespondingmodeofint2?/etolatticemisfitatalsublatticetobesimilartothatatnisublattice,resultinginbeneficialductilityeffectofcrtoni-ni3 alalloysystem.inaddition,crisfoundtoonlyaffectthevalueofint2?/eatthesiteitsubstitutes,havingalmostnoinfluenceonthoseatothersites,demonstratingthattheductilityeffectofcrislocal.(6)theformationenergyanalysisofointheni-ni3alsystemwithoutcrshowsthatthephasepreferringofcrisaffectedbyboththecompositionandspaceoftheinterstitialsiteitenters:ononehand,attractedbynicontent,opreferstosegregatetoniphaseregionfirstly,andthentheni/ni3a1 interfaceregionarea,andfinallyni3a1phase;ontheotherhand,oinniphaseregionwillsegregatetoni/ni3a1interfaceregionorni3a1 phaseregionwhenniphaseiscompressedtoacertainextent.inaword,oprefersni-richinterstitialsitewithlargespace.(7)theanalysisoftheformationenergyofointheni-ni3alsystemwithcrshowsthatcrdoesnotinfluencethephasepreferringofotolooseandni-richinterstitialsite,butcrespeciallythatinniphasecandecreasetheformationenergyofo.