Yield Behaviors Of Bulk Amorphous Alloys

Because of their unique disordered structure and excellent mechanical, physical and chemical properties(e.g., high wear resistance, high corrosion resistance, high strength, high elasticity, low modulus, antioxidantion, excellent soft magnetic properties, etc.), bulk amorphous alloys(BAAs) have broad application prospects. However, their low plastic formability at room temperature are major obstacles to usage of much bigger industry scale. A systematic study about effects of stress state on the shear binding of BAAs has a very important scientific significance for finding and preparing these alloys with better ductility and provide a scientific basis for their practical applications.In this paper, the influence of stress state and hydrostatic pressure on the yielding behaviors in BAAs was investigated. The main research is the following: effects of uniaxial stress state and complex stress state on the yield behaviors of BAAs; numerical simulation of the yield behavior of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 BAA under the sleeve restriction; comparison the yield behavior adaptabilities of BAAs between Mohr-Coulomb(M-C) criterion and Drucker-Prager(D-P) criteria. The main results are summarized as follows:(1) Under uniform axial extension, the values calculated based on DP2 are the same as these from M-C, and the value calculated from DP1 is closer to the experimental value than that from M-C; under complex stress state, taking the effect of hydrostatic pressure on the material into account, the D-P model has a more accurate description about yielding.(2) The shear and plastic behaviors of BAAs depend on the geometry and the stress state of the sample; the hydrostatic pressure is not associated with fracture angle and internal friction coefficient of the materials; under tensile or compressive load, the influence of hydrostatic pressure on the yield behavior of BAAs is equivalent to a superposition of normal stress, and either the shear yielding or fracture is inhibited by hydrostatic pressure; the effect of hydrostatic stress is equivalent to that of normal stress.(3) The yielding behavior of a Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 BAAs confined by a copper sleeve was modeled using ABAQUS: the yielding strength of the studied alloy is 2003 MPa calculated based on M-C criterion, and its value is 1776 MPa calculated based on D-P criterion; in the numerical simulation, the predicted value from D-P criterion is closer to the experimental values than that from M-C criterion. under a copper sleeve restriction condition, the D-P criterion is more suitable for describing the yielding of amorphous alloys than M-C criterion; under a restriction of copper the sleeve, the existence of hydrostatic pressure promotes the increase of free volume content and the heterogeneity of free volume distribution in BAAs, and thus induce the the heterogeneity of stress and strain distribution in the corresponding materials.