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The effect of alloying concentration x (x=0~2.2%,atom fraction) to several parameters such as Cauchy pressure, Elastic modulus E, the shear modulus G and their ratio G/B₀ of B₂-NiAl supercells alloyed by Cr and Ce, alone or together, are calculated in the framework of Virtual Crystal Approximation by the first-principles pseudopotential plane-wave method. The shear modulus G and elastic modulus E of B₂-NiAl alloy were significantly increased when Cr occupied the Ni atom site in B₂-NiAl crystals, while the G and E will be reduced when Ce occupied the Al atom site. With the alloying concentration increased to 2.1%, the ductility of B₂-NiAl crystals can be improved with Cr occupied the Al atom site. It is worth emphasizing that the ductility of B₂-NiAl crystals was improved more significantly when Ce and Cr replaced Al atom site simultaneously than that alloyed by Ce or Cr alone, especially the alloying concentration x is 2.0%. The electronic density of states shows that Cr atoms or Cr cooperation with Ce atoms all can weaken the hybridization effect of the main bonding peaks of Ni(d)-Ni(d) and decrease the directivity of the main bonding peaks in B₂-NiAl crystal. The calculation result herein explains the phenomenon that the room temperature ductility of B2-NiAl alloy is enhanced obviously alloyed by Cr or Cr cooperation with Ce.