Investigation On Thermal-mechanical Coupling Behavior And Performance Of TiB₂/Ti6Al4V Laminated Composites By Selective Laser Melting

In the process of selective laser melting（SLM）forming multi-material,the interface bonding performance has an important effect on the forming quality of the multi-material components.In this paper,a three-dimensional finite element model based on ANSYS software was proposed to quantitatively analyze thermal behavior and stress behavior at the interface of SLM formed TiB₂/Ti6Al4V multi-material.The effect of thermal behavior on the metallurgical bonding at the interface of multi-material and the effect of stress behavior on the mechanical properties of parts were investigated by the combination of experiments and simulations.The interface reaction mechanism and interface bonding strength of multi-material were further discussed.The thermal behavior analysis at the interface showed that the maximum temperature gradient was located at the interface.With the increase of laser power,the maximum temperature gradient increased significantly from 24.9°C/μm to 37.8°C/μm,and was not sensitive to changes in scanning speed.The increase of interfacial temperature and liquid lifetime helped the remelted liquid of the formed Ti6Al4V layer to wet the TiB₂ unmelted particles,forming a good interfacial bonding.Based on the thermo-mechanical coupling results,it was further found that the thermal stresses in the x and y directions were significantly lower than the thermal stresses in the z direction,that is,the maximum thermal stress in the building direction was the most likely to cause interlayer cracks.After the forming component was completely cooled,the remaining tensile stress inside the component became the residual stress,and this value increased continuously with the increase of laser power or scanning speed.By combination of the simulation and experimental results,it was found that at a laser power of 400 W and a scanning speed of 600 mm/s,the appropriate interface temperature（2453°C）and liquid lifetime（1.7 ms）made the remelted Ti6Al4V layer of the appropriate size.There was no pores and unmelted particles at the interface,and the residual stress would not cause the material to deform and crack,achieving a good interface bonding between the TiB₂ layer and the Ti6Al4V layer.In addition,the microstructure of the TiB₂/Ti6Al4V multi-material component under this process parameter was also studied.The results showed that TiB whiskers was formed at the interface by the in-situ reaction between the TiB₂ particles and Ti6Al4V liquid phase,which was beneficial to interfacial bonding.In the TiB₂ layer,compared with the center of the molten pool,due to the more Ti6Al4V liquid phase at the bottom of the molten pool,the aspect ratio of the TiB was higher.The microhardness value of TiB was median,which made a gradient distribution of the microhardness at different material layers.The bending strength of TiB₂/Ti6Al4V multi-material components formed by SLM reached 1957 MPa,which was higher than that of pure Ti6Al4V（1608 MPa）.The results proved that the interfacial bonding performance of multi-materials was good under this parameter.