Serrated Plastic Instability Behavior And Numerical Investigation Of Metastable β Ti-12Mo Alloy

Metastable βTi-12Mo alloy is regarded as a promising orthopedics embedded material,due to their high strength-to-weight ratio,good corrosion resistance and excellent biocompatibility.However,a type of plastic instability,namely Portevin-Le chatelier（PLC）effect has been observed in metastableβTi-12Mo alloy,which results in a dramatic reduction of material elongation,fatigue lift and surface quality,ultimately affecting the processing and application prospects of the alloy.To reveal the spatiotemporal behaviors of the PLC effect and accurately predict the instability range of the applied strain rate,a combination of theoretical analysis,uniaxial tensile test and numerical simulation are used in this paper.The Main research contents and conclusions are as follows:（1）Using cold crucible levitation melting and cold rolling techniques,the metastableβTi-12Mo alloy specimens were prepared.The influence of applied strain rate on mechanical properties and the evolution of the spatiotemporal behaviors of the PLC effect as well as its mechanism in metastableβTi-12Mo alloy are investigated by uniaxial tensile test coupled with DIC technique.The results show that the yield stress and the tensile strength of metastableβTi-12Mo alloy decrease with the increase of applied strain rate.Besides,the value of the stress drop magnitude and the stress drop period decrease with the increase of applied strain rate.（2）A uniaxial tensile FE model embedded in the Mc Cormick’s constitutive model was developed using the UMAT subroutine in the ABAQUS/Implicit environment,which can simulate the spatiotemporal behaviors of the PLC effect in metastableβTi-12Mo alloy and the accuracy of the FE model was subsequently verified.Subsequently,based on the above FE model,the evolution of the spatiotemporal behaviors of the PLC effect in the alloy was investigated with different deformation extent and applied strain rates.The results suggest that the stress drop magnitude,the stress drop period and the velocity of PLC band increase with increasing strain or decreasing applied strain rate.However,the width of PLC band decreases and the propagation type of the PLC band transform type A to type A+B as the applied strain rate decreases.Besides,the predictive instable region of the applied strain rate in metastableβTi-12Mo alloy is 1.3×10^-5～1.85×10^-2 s^-1.（3）Based on the above FE model,the effect of the specimen mesh size and specimen thickness on the spatiotemporal behaviors of the PLC effect were investigated.The results indicate that as the specimen mesh size increases,the average stress drop magnitude,the periodic stress drop and the velocity of the PLC band decrease,the width of the PLC band increases and the propagation type of the PLC band shifts from type A+B to type A.In addition,with the increase of the specimen thickness,the value of the stress drop magnitude,the average of the stress drop period and the velocity of the PLC band increase,while the average width of the PLC bands did not change significantly.Meanwhile,the PLC band shifted from type A+B to type B.