Research On Laser Additive Preparation Of Bulk Amorphous Alloy And Its Forming Mechanism

Bulk metallic glasses?BMGs?show excellent performance in physical,chemical,and electrochemical aspects due to their unique short-range ordered and long-range disordered atomic structures.It has broad application prospects in aviation,automotive,electronics,medicine and other fields.However,the traditional preparation process has many problems in size,shape,crystallization,which seriously limits its development and application.Laser additive manufacturing technology is a bottom-up rapid prototyping technology that can directly manufacture metal parts with complex shapes and has a high heating and cooling rate,which provides new ideas for the preparation of BMGs.In this paper,Zr₅₀Ti₅Cu₂₇Ni₁₀Al₈?Zr50?metallic glass samples were prepared under different process parameters using selective laser melting?SLM?technology to study the influence of process parameters on forming quality.The temperature field during the forming process was simulated and calculated using the finite element method to research the thermal effect during the forming process.Experiments were carried out by laser additive to prepare BMGs.Combining the results of experiments and simulations,the crystallization behavior and forming mechanism of BMGs prepared by laser additive were researched.Main conclusions were as follows:During laser additive manufacturing of Zr50 metallic glass,The increase in laser power and the decrease in scanning rate increase the energy obtained per unit volume of material,thereby improving the forming quality and reducing defects.But too high energy will widen the heat-affected zone?HAZ?and promote the crystallization.The surface roughness of the deposited layer will affect the flatness of the powder layer and thus the forming quality.When the angle of laser scanning between deposition layers increases,the flatness of the powder layer of the welding bead decreases,the forming quality decreases,and the defects increase significantly.The simulation results show that the heating and cooling rate of the molten pool and HAZ during the forming process far exceeds the critical heating rate and critical cooling rate of the metallic glass,so theoretically,crystallization can be avoided during single-point and single-pass forming.However,in the single-layer forming and multi-layer forming processes,there is a superposed area of the HAZ between the bead and the deposited layer.The structural relaxation in the superposed area will accumulate multiple times,which promotes the occurrence of crystallization.A 15 mm×15 mm×15 mm Zr50 metallic glass sample was prepared using SLM technology.There are slender peak-like crystallized regions in the sample,and the crystallized phase is mainly Al₅Ni₃Zr₂.The distribution and shape of the crystallized regions are similar to the superimposed regions of the HAZ in the simulation results.During laser additive manufacturing of BMGs,the extremely high heating and cooling rate can avoid crystallization in the molten pool and part of the HAZ.However,the superimposed zone of the HAZ undergoes multiple transformations of the HAZ,which continuously accumulates structural relaxation and crystal embryo,eventually leading to crystallization.