Study of thermal behavior and microstructure formation mechanism of CuCrZr alloy melted by laser powder bed fusion

Abstract

The properties of CuCrZr alloy parts subjected to laser powder bed fusion (LPBF) are severely affected by the thermal behavior of the molten pool in relation to the solidified structure. Detailed understanding of the changes in the thermal behavior of the molten pool and the relationship between the thermal behavior and the solidified structure are required to achieve high-performance LPBF parts. In this study, a numerical simulation of temperature field changes was used to model the heat transfer and molten pool characteristics during the LPBF of CuCrZr alloys. The effect of linear energy density (LED) on the morphology and flow of the molten pool was studied using a finite element model (FEM), and the microstructure of the alloy was analyzed in combination with the temperature field. The results show that the shape of the molten pool obtained by the simulation is approximately circular, which differs from the typical comet-shaped molten pool for other alloys. The LED affects both the size of the molten pool and the flow of bubbles in the melt. When the LED is 800 J/m, the size of the molten pool is optimal, the bubbles in the melt can escape smoothly, and the highest relative density is achieved (98.23±1.4%). The simulation results are also in good agreement with the experimental data. The simulation obtained the difference in the temperature gradient along different directions as well. This anisotropy caused the solidified structure to form a large number of equiaxed crystals in the horizontal plane. At the same time, the circular shape of the molten pool caused a large deflection in the temperature gradient direction. The grain orientation of the horizontal plane formed an angle of 45° to the scanning direction. As a result of this larger temperature gradient in the vertical plane, a large number of columnar crystals are epitaxially grown.