Studing On The Phase Equilibrium Of Al-M-Re(M=Cr,Cu,Si,Zr) Systems And The Structures And Properties Of Some Intermetallic Compounds In These Systems

The isothermal section of ternary Al-(Cr, Zr)-Ho systems at773K were investigated, and the structures and properties of some intermetallic compounds in Al-RE and Al-(Cu, Si)-RE systems were also estimated by using first principles. The main results are listed as follows:(1) The phase relationship of Al-Cr-Ho system at773K was determined by a combination of XRD and SEM. Phase relations at773K are governed by14three-phase regions,29two-phase regions and15single-phase regions. The existences of10binary compounds and two ternary phases have been confirmed. Al11Cr2, Al11Cr4and Al17Ho2were not found at773K in this work. No remarkable solid solubility could be found in the isothermal section of the Al-Cr-Ho ternary system at773K. The crystal structures of Al9Cr4and Al8Cr4Ho were determined by using XRD and Rietveld method.(2) The phase relationships in the Al-Zr-Ho ternary system at773K have been investigated in the whole compositional range. The existences of13binary compounds and a ternary compound have been confirmed. The solubility of Zr in Al2Ho, AlHo and Ho is about71at.%,6at.%and12at.%Zr, respectively. No remarkable solid solubility could be found in the other compounds of the Al-Zr-Ho ternary system at773K.(3) Some important properties of hexagonal Al3RE (RE=La, Ce, Pr, Nd, Sm and Gd) intermetallic compounds are calculated by using first-principles calculations with LSDA+U. The results of cohesive energy indicate that these compounds can be stable under absolute zero Kelvin. Al3La, Al3Ce, Al3Sm and Al3Gd are mechanically unstable, while Al3Pr and Al3Nd are stable. All the compounds are brittle material.(4) The dependences of the structural, electronic, mechanical and thermodynamic properties of AlSc2compound on pressure (0-50GPa) were investigated by means of the first-principles method with GGA and LDA. It was found that the pressure has significant effects on the equilibrium volume, mechanical properties, electronic properties and the heat capacity. The Debye temperature can be obtained from the elastic constants and the sound velocities and the pressure has little influence.(5) An investigation into the structural, electronic and elastic properties of of AlCu2M (M=Sc, Ti and Cr) compounds in the range0-50GPa was investigated using first-principles method with GGA. The bulk modulus, shear modulus and Young’s modulus increases with increase in pressure, which indicates that increasing pressures can improve the materials hardness. The electronic densities of states and bonding charge densities have been discussed in details.(6) An investigation into the structural, electronic, elastic and thermodynamic properties of AlSi2RE (RE=La, Ce, Pr and Nd) compounds was investigated using first-principles calculations with GGA. We present a combination of the GGA and the LSDA+U approaches to investigate the electronic structures of AlSi2RE compounds in order to obtain the appropriate results. The bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio v of polycrystalline AlSi2RE compounds were determined using the Voigt-Reuss-Hill (VRH) averaging scheme. The thermodynamic properties for AlSi2RE compounds were also calculated.