Influence of processing parameters on the evolution of melt pool, porosity, and microstructures in Ti-6Al-4V alloy parts fabricated by selective laser melting

Abstract

Selective laser melting involves melting and solidification of metal powder particles in a track-by-track and layer-by-layer method to fabricate 3D parts. The present investigation focuses on understanding the effect of laser power and scan speed on the evolution of melt pool, porosity and multiple thermal cycling effects on the microstructure in parts fabricated using selective laser melting. In this study, Ti-6Al-4V pre-alloyed powder was used to produce single-track deposits and bulk parts. Using different combinations of laser power and scan speeds, single-track deposits and bulk parts were produced. The cross-sections of the single-track deposits and bulk samples were prepared for metallographic observations and the melt pool shape and size and porosity were evaluated. When a low energy density was applied the un-melted powder particles produced irregularly shaped porosity, and a high energy density resulted in rounded porosity, which was due to keyhole effects. The samples produced with a proper combination of power and speeds were fully dense. Further, microstructural development under the influence of process condition was highlighted. Overall, the study demonstrates a good correlation between the single-track melt pool geometries, porosity in bulk parts and also demonstrates the microstructural inhomogeneity during deposition.

A review of metal additive manufacturing technologies: Mechanism of defects formation and simulation of melting and solidification phenomena in laser powder bed fusion process

“…If the machine and the powder are managed well, the process parameters that can be controlled in processing are as follows as shown in Fig.22: (1) Laser power; P (W) (2) Scan speed; v (mm/s) (3) Hatch pitch; h (mm) (4) Layer thickness: t (mm) Generally, although the spot size, d, is fixed, it is one of the important process parameters. And also, the following energy density, E, is used frequently as a parameter including those process parameters (Simchi, 2006;Yang et al, 2017;EPMA, 2015;Dilip et al, 2017). In the case of a single track, the following equation is applied.…”

Laser Operating Windows Prediction in Selective Laser-Melting Processing of Metallic Powders: Development and Validation of a Computational Fluid Dynamics-Based Model

“…The calibration analysis has been carried out on five alloys for which measures of track dimensions, part relative density, and total absorptivity are available in the literature [15,24,[29][30][31].…”

“…All the experimental analyses reported in [15,24,29,30] refer to single tracks printed on a single powder bed lying on a platform made of the same alloy. Accordingly, the model simulates only one powder layer of nominal thickness.…”

“…Accordingly, the model simulates only one powder layer of nominal thickness. Results in terms of density of printed cubic specimens realized with different laser parameters and powder layer thickness, are given in [30,31]. To simulate these experiments the effective layer thickness has been simulated.…”

“…All the experiments have been performed with laser systems with 1.06-1.07 µm wavelength. Measures of width and depth are provided in [24,29,30]. Only measures of track cross section area are available in [15].…”