The Preparation And Performance Study Of Amorphous Alloy And Its In-situ Formed Composites

Bulk metallic glasses?BMGs?have wide application prospects in many fields,owing to their unique atomic structure,possessing certain properties of glass,metals,solids,and liquids,and excellent physical,chemical and mechanical properties.However,the amorphous unique atomic structure brings about high strength;it also fails in global plasticity at room temperature similar to that produced by the large-scale dislocation movement of the conventional alloy.In the plastic deformation,the deformation of single-phase metallic glass material will be highly concentrated in a narrow area?shear band?.The unlimited extension of main shear band will lead to catastrophic fracture,which restricts the large-scale application as structural materials for BMGs.Recently,how to overcome the catastrophic fracture of BMGs associated with unlimited extension of a shear band,continuously receives extensive attention of the researchers.In this paper,a series of Ni₆₂Nb_38-xTa_x?x=5,10,15,20,25?alloy rod with critical diameter of 2 mm are developed by copper mold suction casting under an argon atmosphere.The Ni₆₂Nb₁₈Ta₂₀ BMG has shown best thermal stability in the alloy system,and Ni₆₂Nb₂₃Ta₁₅ BMG has shown best GFA in the alloy system based on the analysis of the reduced glass transition temperature T_rgg and the parameter?.The Ni₆₂Nb_38-xTa_x?x=5,10,15,20,25?amorphous alloys rods exhibit high compressive fracture stresses?_c from 2889 MPa to 3291 MPa with the increase of Ta content,among them,the Ni₆₂Nb₁₈Ta₂₀0 BMG has fracture strength of about 3.29 GPa.The nearly linear relationship between the?_c and T_g values,this suggests that the increase of the fracture strength is associated with the increase of glass transition temperature T_g of the alloys with the increase of Ta content.The plastic strains?_p of The Ni₆₂Nb_38-xTa_x?x=5,10,15,20,25?amorphous alloys rods are about 0.76%,0.78%,1.41%,1.36%and0.20%respectively.Considering that shape memory alloys?SMAs?have been recently acknowledged as a very important smart alloy due to their shape memory effect,special super elasticity,excellent toughness,good corrosion resistance and great abrasion resistance.Moreover,shape memory alloys are similar to metallic glass in many ways,such as super elasticity,good corrosion resistance and great abrasion resistance.Aiming to the issue of amorphous alloys and expand the use of shape memory alloys,this paper presents a new engineering concept:based on two kinds of excellent shape memory alloys to design BMG/SMA composites with super elasticity,high strength,high toughness and high plastic deformability,the compositional structure of the composite material is balanced according to the empirical rule of the amorphous alloy forming ability and taking into account the superior performance of the two new alloy materials.Therefore,a series of Cu₄₁Ni₂₇Ti₂₅Al₇ BMG/SMA composites rod with diameter of2 mm,3 mm and 5mm are synthesized by copper mold suction casting under an argon atmosphere,and the phase analysis shows that it contains Cu_0.035Ni_0.565Ti_0.40.40 crystal phase,CuNi₂Ti crystal phase and a small amount of Cu crystal phase.The endothermic behavior before crystallization demonstrates a distinct glass transition with the onset temperature T_g of the Cu₄₁Ni₂₇Ti₂₅Al₇ rod is about 560.4 K,the onset temperature for the first step crystallization?T_x?is about 775.6K,and then the supercooled liquid region?T is about 215.2 K at the heating rate of 20K/min.It shows that good thermal stability and strong plasticity.The room-temperature compression experiments show that the compressive fracture strength?_c of Cu₄₁Ni₂₇Ti₂₅Al₇ BMG/SMA composites rod with diameter of 2 mm and 3 mm are over than 1.7GPa.More importantly,the plastic strain of 11%is obtained for Cu₄₁Ni₂₇Ti₂₅Al₇ BMG/SMA composites.We find out that the Cu₄₁Ni₂₇Ti₂₅Al₇ BMG/SMA composites exhibit ferromagnetism at low temperatures has a large saturation magnetization Ms.The coactivity closed to zero and very small hysteresis loss reflecting a good soft magnetic.The in-situ crystalline phase in the Cu₄₁Ni₂₇Ti₂₅Al₇ BMG/SMA composites can effectively against the catastrophic failure associated with unlimited extension of a shear band in the plastic deformation and overcome the shortcomings of global plasticity.The introduction of shape memory alloys into metallic glasses matrix can not only improve the plasticity of the alloy,but also keep intrinsic excellent mechanical properties.To some extent,SMAs compositing BMGs is a performance optimizing and strengthening process,which has the important exploring and practical significance for both shape memory alloy and metallic glass.It can be used as a structural material into large-scale practical applications,becoming the ideal and widely used new material in the future.