Microstructure Control And Toughening Of Cu-Zr-Al-Ni Amorphous Composites By Microalloying

The formation of amorphous composites is the main technology to improve the room temperature plasticity of amorphous composites.However,the uneven cross-section distribution and agglomeration characteristics of crystalline phases in casting bulk metallic glass composites?BMGCs?result in low room temperature plasticity of the composites,which restricts the engineering application of casting BMGCs as structural materials.Endogenous B2-CuZr phase in CuZr-based amorphous composites can effectively prevent the rapid expansion of shear bands,promote the proliferation and interaction of shear bands,and induce martensitic transformation,thus exhibiting good room temperature plasticity and"work hardening"characteristics.Therefore,B2-CuZr/CuZr-based amorphous composites are considered to be the most promising amorphous materials in engineering applications and become a research hotspot in the field of amorphous materials.In this paper(Cu₄₇Zr₄₇Al₆)₉₉Ni₁ system amorphous alloys were selected,and different contents of Ta,Nb and Sn were added to improve the uniformity of B2-CuZr phase distribution in the larger casting cross section,so as to achieve toughening effect.In this research,a raw material with a purity of 99.9%was used.The?=4 mm specimens with nominal compositions of(Cu_0.47Zr_0.47Al_0.06)_99-x9-x Ni₁Ta_x?x=0,0.5,1,2at.%?,(Cu_0.47Zr_0.47-Al_0.06)_99-xNi₁Nb_x?x=0,0.5,1,2 at.%?,(Cu_0.47Zr_0.47Al_0.06)_99-xNi₁Sn_x?x=0,0.5,0.75,1 at.%?were prepared by vacuum copper mold suction casting.The effects of Ta,Nb and Sn on the microstructure and mechanical properties of amorphous composites were analyzed by X-ray diffraction,metallographic observation,DSC,EDS,compression test and SEM fracture morphology.The results show that proper addition of Ta/Nb/Sn can control the volume fraction of B2-CuZr phase in amorphous composites and improve the uniformity of the cross-section distribution of B2-CuZr phase.The mechanism is mainly attributed to Ta/Nb/Sn improving the amorphous forming ability of the alloy,which is different from the heterogeneous nucleation mechanism of Ta/Nb/Sn in small cross-section.In this experiment,amorphous composites with 0.5 at.%Ta or 0.5 at.%Nb had the best mechanical properties because of their good volume fraction and uniform distribution of B2-CuZr.Among them,the compressive plastic strain and fracture strength of amorphous composites with 0.5 at.%Ta were 3.5%and 2088 MPa respectively,and the compressive plastic strain and fracture strength of amorphous composites with 0.5 at.%Nb were 3.0%respectively.The mechanical properties of(Cu_0.47Zr_0.47Al_0.06)₉₉Ni₁ alloy were decreased by adding Sn and 2008 MPa,because the volume fraction of B2-CuZr in amorphous composites decreased sharply.The results show that the plastic strain of large cross-section Cu-Zr-Al-Ni amorphous composites depends on the volume fraction of B2-CuZr phase and the uniformity of distribution?the ratio parameter of precipitated phase size to spacing?=r_s/?_s?.The relationship between them satisfies the equation:epsilon?_p=0.1×?0.46-??^-2.In this experiment,0.5 at.%Ta or 0.5 at.%Nb were added to realize the effective regulation and toughening of the structure of Cu-Zr-Al-Ni amorphous composites with large cross-section??4mm?.