Deformation Mechanisms Of In-situ Metallic Glass Matrix Composites Reinforced By Dendrites Upon Room-temperature Tension

Owing to their unique amorphous structures,bulk metallic glasses?BMGs?,compared with traditional crystalline alloys,are well-known for their unique mechanical properties,such as the high yield strength,large elastic limit,and high hardness,together with excellent corrosion and wear resistance,etc..Nevertheless,due to the rapid development of highly-localized shear bands upon loading at ambient temperature,BMGs usually exhibit poor ductility and fail catastrophically,which greatly restricts their applications as potential structural engineering materials.In order to retard rapid shear banding in BMGs and promote the generation of multiple shear bands,metallic glass matrix composites?MGMCs?reinforced by in-situ secondary dendritic phases have been successfully developed to enhance room-temperature plasticity effectively.?1?Ti-based metallic glass matrix composites?MGMCs?with a composition of Ti₅₀Zr₂₀V₁₀Cu₅Be₁₅?atomic percent,at.%?exhibit excellent tensile ductility and distinct work-hardening capability.According to the analysis to microstructure deformation mechanism,a dislocation pile-up model?DPM?has been established to elaborate the dislocation motion near the yield point.The hardness variation in the dendrites,the strengthening effect from unloading-reloading tests and the analysis of TEM to deformed samples prove the reasonability of the DPM during tension.A linear Hall-Petch-like relationship between the yield strength,?,and the inverse square root of the diameter of dendrite arms,d^-1/2 has been theoretically derived based on DPM.The materials constant,k,in the present Hall-Petch-like relationship can be calculated on the basis of the pile-up model,and is very close to the experimental value.The Hall-Petch-like relationship is verified for a variety of MGMCs,whose plastic deformation is only dominated by dislocation motion.?2?Mean-field theory?MFT?has been first utilized to build a relationship between the critical diameter of dendrites,dc,and the composition in MGMCs with the similar atomic percentages of low solubility elements.According to the double logarithmic curves,it is obvious that smaller diameters follow a power-law distribution,while the larger diameters do not follow a power-law distribution,but decrease exponentially in probability.A MFT predicts the complementary cumulative distribution function of the diameter of dendrite arms,d,to indicate the dependence of the diameter to the ratio,?.By tuning the composition,one can universally scale the Hall-Petch-like relationship,and accurately predict the yield strength of such in-situ MGMCs.?3?The dendrite size of MGMCs is also dependent on the cooling rate during preparation.The more size of sample is,the lower cooling rate is.MFT has been first utilized to build a relationship between,d_c,and the size of samples in MGMCs with the same composition.MGMC with the same composition have been prepared into varying sizes of samples.MFT predicts the complementary cumulative distribution function of the diameter of dendrite arms,d,to indicate the dependence of the diameter to the size of samples.By tuning the size of sample,one can universally scale the Hall-Petch-like relationship,and accurately predict the yield strength of such in-situ MGMCs.In this study,the deformed mechanism of in-situ MGMCs at yield point has been analyzed to build the quantitative relationship between the microstructure and yield strength.Statistical analysis of data,based on MFT,is utilized to build the quantitative relationship between composition/size of samples and microstructure.Therefore,the yield strength of MGMC can be regulated accurately by the design of composition and size of samples.