Microstructure And Mechanical Properties Of Ti-based Bulk Metallic Glass Composites Ductilized By The B2-structured Phase

The catastrophic embrittlement of bulk amorphous alloys at room temperature becomes the"Achilles’heel".The reason lies in the rapid expansion of local shear bands.It is found that martensitic transformation will occur during deformation by introducing metastable second phase,which can enhance the toughness of the material,thus make up for the strain softening of the amorphous matrix in plastic deformation,and improve the working hardening ability of the material.However,the morphology of the second phase of the"phase transition induced plasticity"ductile plasticized bulk amorphous composites is not easy to control.This problem is particularly prominent in Ti amorphous alloy systems,and the distribution of metastable second phase is not dispersed.The toughening plasticization of crystal phase is greatly weakened.Based on the above problems,this paper tentatively regulates the precipitated phase by Nb microalloying and heat treatment processes in order to optimize the morphology characteristics of the second phase,and further studies the microstructure,martensitic transformation,mechanical properties and deformation behavior characteristics of the ductile plasticized bulk amorphous composites.The main contents and conclusions of this paper are as follows:（1）In Ti₄₅Cu₄₁Ni₉Zr₅bulk amorphous composites,0.4～0.6%Nb elements were added in trace amounts to diffuse the B2-（Ti,Zr）（Cu,Ni）phase and improve the strength and plastic deformation of the materials.When the Nb element content is0.6,Compared with the pure amorphous material,the comprehensive mechanical properties of the material are improved obviously,the strength is 2250.5 MPa,the compressive plasticity is 8.5%.The improvement of the material properties is due to the Nb solution promoting the nucleation of metastable b2 phase.（2）the samples with selected nb content of 0.2%and 0.6%were annealed at190℃,290℃and 390℃for 0.5 h,respectively.The results show that the Nb content of 0.2%alloy after 190℃annealing treatment,B2 crystal phase volume fraction and grain size in the sample increased,and accompanied by the precipitation of nanocrystalline phase,the sample appeared work hardening phenomenon.after 190℃annealing,the plastic deformation capacity of the sample was about 1%stronger than that of the as-cast titanium,and the strength was equivalent to that of the as-cast sample.It shows that the microalloyed samples can select the appropriate annealing temperature at low crystallization volume fraction,which can effectively control the crystal phase volume fraction and grain size inside the alloy,and improve the comprehensive mechanical properties of titanium based amorphous composites.