The Research On Structure And Mechanical Property Structure Of Cu-based Bulk Amorphous Alloy

Multiple bulk amorphous alloys have many potential applications resulting from their unique propertites,such as superior strength and hardness,good room-temperature elasticity and excellent processability.While advances in amorphous metallic alloy have been impressive,they have been made largely through experimrntal development.And the microstructure and deformation behavior of amorphous alloys is the hot spot of the current research.In this paper,the microstructure and mechanical behavior of Cu-based bulk metallic glasses were investigated.The main content are as follows:The microstructure changes in cone samples of Cu₅₀Zr₄₂Al₈ amorphous alloys were analysed and studied.When the taper shape of Cu₅₀Zr₄₂Al₈ is less than 4.8mm,the microstructure of alloy has a full crystalline phase.When the the taper shape of Cu₅₀Zr₄₂Al₈ is more than 4.8mm,the microstructure of alloy can result in the formation of a composite consisting of part of amorphous crystals and part of crystals.The results show that,as the cooling rate changes,surface amorphous alloys region,the fine center equi-axial crystals region and transition region between the two exist respectively in the cone sample.The micro-hardness of bulk amorphous alloys can change in the structural relaxation.From amorphous region to amorphous /crystal transition region,before annealing,the hardness increased gradually to reach maximum value,and the Maximum hardness was 713HV,then the hardness went to decrease gradually.After annealing,hardness decrease at the first and then increased gradually to reach maximum value,the Maximum hardness was 734HV.In amorphous region,the hardness decreased gradually from the centre to the surface before annealing.The hardness increased gradually from surface to centre after annealing.In amorphous/crystal transition region,the hardness increased gradually from centre to surface before annealing.The hardness decreased gradually from the centre to the surface after annealing.The micro-hardness of amorphous sample had the trend of entre increase after annealing.So appropriate heat treatment is used in order to improve the hardness of amorphous/crystal composites.The micro-region mechanical behavior and plastic deformation mechanism of Cu₅₀Zr₄₂Al₈ amorphous alloys from glassy region to amorphous / crystal transition region were studied by nanoindentation technology.The nano-hardness and reduced modulus of Cu₅₀Zr₄₂Al₈ amorphous alloys cone samples average value is 18.63GPa and 196.55GPa separately in the amorphous region,15.48GPa and 178.05GPa separately in the amorphous/crystal transition region,16.71GPa and 185.38GPa separately from amorphous region to amorphous / crystal transition region.Small plastic and elastic deformation exhibit in the glassy region,and the hardness is higher.Lower hardness and elastic modulus,severe plastic deformation exhibit in the amorphous/crystal transition region.This paper also discussed the effect of annealing treatment on Cu₅₀Zr₄₂Al₈ compressive mechanical properties.After isothermal annealing over the Tx,the crystal phase of Cu₁₀Zr₇ and AlCu₂Zr performs startly and the Cu₁₀Zr₇ is more than the other. The specimens has been fully crystallized at 973K.In the crystallization process,the compressive strengths and fracture morphology have no difference at quenching,400K and 600K,performaning uniform distribution of vein patterns.The compressive strength reaches maximum after isothermal annealing at 743K.The compressive strength morphology is not uniform distribution of vein patterns.It shows some vein patterns in the annealing temperature 753K.The minimum compressive strength appears at 873K;there is basically no the character of amorphous alloy in the fracture morphology.After isothermal annealing of 973K,the compressive strength is higher than 873K.The fracture morphology was significantly different from amorphous alloy, performaning typical brittle fracture.Different cooling processes have influence on structure and micro-hardness of Cu₅₀Zr₄₂Al₈ amorphous alloys after crystallization.It may give rise to the different precipitated phase after crystallization.Thus the amorphous structure and mechanical behavior are Different.The microhardness of as-cast sample was 756 HV,the air-cooling sample hardness was 555 HV,the hydrocooling sample was 650 HV,the liquid nitrogen-cooling sample hardness was 680 HV.