Simulative Study For Structures And Elastic Mechanics Of High Entropy Alloys And Superalloy

In numerous high entropy alloys?HEAs?,those that can be regarded as the refractory HEAs composed of refractory metals?Ti,V,Cr,Zr,Nb,Mo,Hf,Ta,W?adopt the body center cubic?BCC?structures.Due to their potential applications at elevated temperature,and in order to reduce the mass density,the elastic properties of a large number of experimental studies of refractory high entropy alloys.In this thesis,we use the ab into method in combination with the coherent potential approximation to study the elastic properties of single-phase solid solution Al_x CrFeMoTi high entropy alloys.We mainly focus on the effect of Al doping on the structure and elastic properties of refractory high entropy alloys.And we also study that the refractory metals produce an influence on the elastic behavior of the cobalt based superalloys.The elastic constants and the polycrystalline elastic modulus of CoAl Mo and FeAlMo superalloys in face-centered cubic structures are discussed in detail by using the first-principles method based on density functional theory.The Poisson's ratio of the CoAlMo superalloy is v=0.199 and the Poisson's ratio of FeAlMo is v=0.From the criterion of plasticity and brittleness of the material,when the Poisson's ratio is more than0.31,the alloy material is plastic,When Poisson's ratio is v<0.31,the alloy material is brittle.Through the Poisson's ratio,the two alloys show more brittleness.By calculating we also get CoAlMo Platts ratio B/G=1.33,FeAlMo Platts ratio B/G=1.66.When Platts ratio B/G<1.75 indicates that the material is brittle,the Platts ratio B/G>1.75indicates that the material is ductile.The Platts ratios of the two alloys also prove that they are brittle.Studies have shown that this brittleness has a certain relationship with the Al content.Therefore,we can change the content of aluminum to get some of the better ductility of the superalloy.We also calculated the special form of the quaternary high-entropy alloy,the quaternary Heusler alloy,and the results show that not all Heusler alloys meet the priority occupancy rules.From the decreasing trend of Poisson's ratio of NiCoNiAl,NiFnNiAl,NiMnNiAl and NiCrNiAl,the plasticity of the traditional Heusler alloy is weakened and the brittleness is gradually enhanced with the decrease of the atomic number at the B position.