Thermodynamics And Mechanical Propertys Of CuZr Based Bulk Metallic Glasses

The glass forming ability, thermodynamics and mechanical properties of the CuZr based bulk metallic glasses have been investigated in this thesis.Cu45Zr48Al7 was worked as master alloy because its the best glass forming ability. Cu45Zr48-xAl7Nbx(x=0, 1, 2, 3, 4, 5) have been prepared by copper mold casting method. The glass forming ability of Cu45Zr48-xAl7Nbx was researched by using XRD and DSC. The results showed that Cu45Zr45Al7Nb3 had the best glass forming ability and adding the element of Nb enhanced the glass forming ability of the CuZrAl alloy.The thermodynamic properties of Cu45Zr48Al7 and Cu45Zr45Al7Nb3 bulk metallic glasses were investigated by means of DSC. The activation energies for the crystallization were evaluated by Kissinger's equation. The results showed that the crystallization process of Cu45Zr48Al7 and Cu45Zr45Al7Nb3 bulk metallic glasses can be regarded as a thermodynamic phase transformation process. The crystallization activate energy of Cu45Zr45Al7Nb3 was bigger than that of Cu45Zr48Al7, which indicated that Cu45Zr45Al7Nb3 had higher thermal stability. The addition of Nb improved the degree of confusion. All of these restrained separation of primary phase, which enhanced crystallization energy and thermal stability.The compression properties, the hardness and nano-mechanical properties in room temperature had been studied. The results showed that the fracture strength of Cu45Zr45Al7Nb3 was higher (Stress 1855 MPa,Strain 9.6%). The micro-hardness, nano-hardness and Young's modulus of Cu45Zr45Al7Nb3 metallic glass were bigger, and it had smaller nano-scratch and friction coefficient. While after annealed 60 minutes of Cu45Zr45Al7Nb3 metallic glass, it had contrary result. All of these revealed that annealing treatment can enhanced plasticity of Cu45Zr45Al7Nb3 bulk metallic glasses.The tribological properties of Cu45Zr45Al7Nb3 bulk metallic glasses were investigated too. The results showed that the wear resistance decreased clearly after annealling treatment because of the separation of crystal phase.