Laser 3D Printing Of Controllable Fabrication Of Graded Metallic Glass Composite

Introducing crystalline phases into glassy matrix to produce bulk metallic glass composites(BMGC)is an effective route to improve the ductility of monolithic bulk metallic glasses.However,the presence of crystalline phases severely decreases the strength.Here,to achieve a desirable strength-ductility synergy,a novel gradient structure,composed of multiple layers with gradient volume fraction of crystalline dendrite,is well-controllably fabricated by the laser 3D printing technology.In this paper,we selected Zr39.6Ti33.9Nb7.6Cu6.4Be12.5 bulk metallic glass composites as the research object,and prepare Zr-based bulk metallic glass composites with a novel gradient structure.To realize a controllable fabrication of such a graded structure,we firstly highthroughput ascertain the correlation between processing variables and crystalline volume fraction through rapid synthesizing a series of metallic glass composite samples by the laser 3D printing under continuously changed combinations of laser power and scan speed.The morphology,microstructure and mechanical properties of samples were analyzed by means of SEM,TEM,room temperature tensile test and microhardness test,and the mechanism of strength-ductility synergy is well explained.A series of samples of metallic glass composites were synthesized rapidly by single channel experiment of laser 3D printing under different process parameters.The results show that the line energy density determined by laser process parameters is controlled by changing the cooling rate.Under the guidance of the functional relationship between the line energy density and the volume fraction of crystalline dendrite,the multiple-layer samples with the gradient volume fraction of crystalline dendrite were prepared by laser 3D printing technology.The obtained graded metallic glass composites shows a much pronounced yield strength without sacrificing the ductility,as compared to the as-cast samples.It is shown that this evasion of strength-ductility trade-off is due to the sequenced plastic deformation and fracture processes from the first layer to the last layer.The graded BMGC also exhibits a strain hardening stage followed by a strain softening stage in the tensile deformation process.This extraordinary deformation behavior is inherently controlled by the competition between strain-induced hardening of the crystalline dendrites and strain-induced softening of the glassy matrix.