Influence of process parameters on the microstructure, and geometrical characteristics of laser additive manufactured (LAM) titanium alloy composite coatings

The study experimentally investigates the effects of Ytterbium Laser System process parameters on the resultant microstructure of Ti-6Al-4V grade 5 alloy and reinforcement powders. The deposition process was conducted employing a 3 kW (CW) Ytterbium Laser System (YLS-2000-TR) machine, coaxial to the reinforcement powder. The laser scanning speed and power were varied between the intervals of 0.8-1.0 m/min and 900-1000 W. All other parameters kept constant were the rate of gas flow, the spot diameter, and the rate of powder flow. Metallurgical studies were conducted where all the samples microstructure was characterized by employing Scanning Electron Microscopy (SEM) and Optical Microscopy (OM). The results showed that a minimum porosity was achieved at high laser power complemented with low powder feed rate. The microstructure formed was dominated by columnar grains and martensitic needle-like structures with a formation of beta phase. It was observed that the microstructure was influenced significantly by the two laser speed modes, and the laser power. The grain size and phase structure were influenced significantly by the laser power; increasing it had resulted in larger grains, and a coarser microstructure. The results also showed that the residual stresses of the optimized specimens were compressive.