Additive manufacturing is a commercially competitive manufacturing technique with the possibility of altering the entire perception of design and fabrication. It offers suitable capabilities for the building and repairing applications in the aerospace industry, which usually requires high level of accuracy and customisation of parts which usually use materials known to pose difficulties in fabrication such as Titanium and its alloys

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. It was concluded that to obtain great mechanical and metallurgical properties (fine grain structure), the process parameters of the LMD process had to be optimised. Metallurgical studies were conducted where all the samples microstructure was characterised 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. Large columnar grains were well-developed, and the epitaxial grain growth was effectively suppressed, which promoted the development of an equiaxed grain structure during the direct laser deposition process. 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 optimised specimens were compressive.

The final geometry and dimensions of the multiple scanned tracks cladded were influenced independently by the intensity of the laser power input and the scanning speed in the process. The geometrical features of the tracks were elucidated by the magnitude of the laser energy density. The microstructure on either side of the scanned tracks had changed contingent to the solidification of the molten pool and its temperature rates and compositional gradients. It was observed that the microstructure was influenced significantly by the two laser speed modes, and the laser power. Large columnar grains were well-developed, and the epitaxial grain growth was effectively suppressed, which promoted the development of an equiaxed grain structure during the direct laser deposition process.


Influence of Process Parameters on the Microstructure, and Geometrical Characteristics of Laser Additive Manufactured (LAM) Titanium Alloy Composite Coatings

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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