Thermal Stress Field and Microstructure Evolution of Ti-6Al-4V Fabricated by Laser Engineered Net Shaping

To investigate the thermal stress field and microstructure evolution of Ti-6Al-4V alloy component produced by laser engineered net shaping (LENS), numerical simulations are performed at both macroscale and mesoscale. At the macroscale, a finite element model is developed and validated by comparing the simulated residual stress with the measured residual stress. Meanwhile, the effect of scanning strategies on residual stress is analyzed. At the mesoscale, a three-dimensional (3D) cellular automaton model is established to analyze the growth mechanism of β-columnar grains. The results show that the maximum residual stress locates at the surrounding area at the interface between the substrate and the cladding layer. Based on the results under the unidirectional and reciprocating scanning strategies, the residual stress of the component is minimized by using the reciprocating alternating scanning strategy. Due to the higher temperature gradient at the bottom of the molten pool, β-columnar grains grow epitaxially from the pre-existing grains in the substrate. When the direction of dendritic growth is consistent with the direction of the temperature gradient, grain growth is faster and there is a clear preferred orientation, which ultimately forms β-columnar grain structures that tilt towards the scanning direction and penetrate multiple cladding layers.

Graphical Abstract