Influence Of Rapid Solidification And Optimized Laser Parameters Relationship On The Geometrical And Hardness Properties Of Ti-Al-Cu Coatings

Abstract

Abstract The development of laser based advanced coatings are continually implemented in order to meet the desired demands and performances of materials in industries. This research paper focuses on the effect of hybrid coating of Ti-Al-Cu on a grade five titanium alloy (Ti-6Al-4V) using laser metal deposition (LMD) process at different laser process parameters. The evolution of the microstructure during the cyclic cooling and heating of the titanium alloy was ascertained by taking the thermal transient measurements which had occurred during the deposits of the layer built.The rates of cooling for the deposited Ti-6Al-4V/Ti-Al-Cu coating was studied to ascertain the influence that the processing parameters had on the morphology during the solidification process. an analysis was conducted that included the ascertaining of the solid-state transmutation which had occurred with the titanium alloy and the microstructural transformation of the Ti-Al-Cu which had occurred during the solidification process. The microstructure and elemental and phase composition of coatings were studied. Ti-6Al-4V/Ti-Al-Cu composites were analyzed using optical microscopy, scanning electron microscopy (SEM) with energy dispersive microscopy (EDS), and x-ray diffraction (XRD). Moreover, the relationships were observed of the factors that governed the microstructural evolution resulting from the processing rates of solidification with the process build parameters from the direct energy deposition laser-based process of Ti-6Al-4V/Ti-Al-Cu composite. The results obtained for the titanium alloy based on microscopy observation revealed that in all subsequent deposits, the microstructure was martensitic and needle-like in structure. Grain refinement was observed within the microstructure as the grains grew in a columnar and dendritic pattern in a counter direction to heat flow. Existence of amorphous phase revealed via XRD was also observed in the coatings. Finally, it was observed that the fast cooling rate (at 1.2 m/min) resulted in fine dendritic microstructure. When the scanning speed was increased, it resulted in longer but finer grains due to decreased energy density to the previously deposited layer, therefore the thickness of the layers was decreased. The Geometry of the coatings was influenced by the interplay of laser power, scanning speed, powder feed rate and melt pool size.