Numerical simulation and experimental investigation of the effect of three-layer annular coaxial shroud on gas-powder flow in laser cladding

Laser cladding is a notable metal additive manufacturing (AM). The outstanding benefit of laser cladding is that the cladding process is more flexible and it can be completed in an open environment. However, oxidation phenomenon of active metals such as titanium alloys will unavoidably clad in the open environment. To solve this problem, a three-layer annular coaxial shroud (TACS) has been designed using computational approach and evaluated by experimental data. A four-stream nozzle of gas-powder computational fluid dynamics (CFD) model was established by employing Euler-Lagrange framework to analyze the powder feeding process. Simulation results show that when the velocities of inner-layer gas of TACS and carrier gas are equal, the powder stream exhibits the best concentration within molten pool area due to the formation of the stable laminar powder stream. When the flared angle of outer-layer gas equals 45°, the vortex toroidal flow moves away from the molten pool and the argon fills in the entire cladding region to form a high-quality barrier. The optimized parameters of TACS have been applied to the practical coaxial laser cladding of Ti-6Al-4V (TC4). A single-track cladding sample with lower height to width ratio and lower wetting angle can be observed due to the flattening of the shielding gas. The oxidation is greatly reduced.