Preparation And Study Of Amorphous Composites With Strain Hardening

Amorphous alloys refer to the alloys with a disordered arrangement of three-dimensional structure.They do not have defects,dislocations and other defective structures,therefore they have many unique and excellent mechanical,physical and chemical properties,such as high strength,high fracture toughness,high hardness,large elastic limit,low elastic modulus and so on.But strain softening is a defect for amorphous alloys,this defect limits the application of metal glass in structural materials.Therefore the ways to overcome this defect has become a breakthrough direction of the application of amorphous alloys.In this paper.we designed and prepared two kinds of amorphous alloys Ti_38.5Ni_38.5Nb_20.5Zr_2.5 and Cu_47.2Zr_47.2Nb_5.6,which have CuZr phase and NiTi phase respectively.The sample has a TRIP effect by controlling the preparation process.The experimental results show that both alloys have stable plastic deformation at room temperature,and the strain hardening in deformation.The new Ti_38.5Ni_38.5Nb_20.5Zr_2.5 bulk amorphous alloy composite with high Nb addition was prepared by rapid solidification of copper mold.The alloy samples show the plastic deformation of 22.1% and the maximum compressive strength.The main components of the composites consist of ? dendrites of Ni-Nb,B2-Ni-Ti shape memory phase and substrate of amorphous alloys.The reason why the alloy has strain hardening is the dislocation and lattice distortion in the crystalline phase,The crystal deformation and the interaction of the shear band inhibit the expanding instability of the shear band,so that the alloy has a large plastic strain.By controlling the sample size,we prepared 1.0mm,1.5mm,2.0mm,2.5mm,Cu_47.2Zr_47.2Nb_5.6 amorphous composite materials successfully.In the Cu-Zr-Nb alloy system,the main component of the sample are amorphous alloy substrate and B2 CuZr martensitic phase which have a diameter of 200 nm.The alloys exhibit good plastic deformation and excellent strain hardening.The plastic deformation of the alloy increases firstly and then decreases with the increasing of the B2 phase in the sample.Especially the sample which has 15% volume fraction of B2 phase,not only have a maximum 12%deformation but also a maximum strain hardening rate,and breaking strength reach to2188.59 MPa.The study shows that the excellent mechanical behavior of the alloy is due to the TRIP effect,which absorbs energy and hinders the instability of the shear band.In this study,both new amorphous composite materials were prepared by alloy composition designing successfully.Amorphous alloy composites have a second phase,which obtained a large plastic deformation capacity and significant work hardening and high strength.This study lays the foundation for the application of toughening agents which were used in the amorphous composite materials.