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

Prog Addit Manuf Influence of processing parameters on the evolution of melt pool, porosity, and microstructures in Ti-6Al-4V alloy parts fabricated by selective laser melting J. J. S. Dilip 0 1 Shanshan Zhang 0 1 Chong Teng 0 1 Kai Zeng 0 1 Chris Robinson 0 1 Deepankar Pal 0 1 Brent Stucker 0 1 0 3DSIM , 1794 Olympic Parkway, Suite 110, Park City, UT 84098 , USA 1 & J. J. S. Dilip 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. Additive manufacturing; Selective laser melting; Ti-6Al-4V alloy; Single-track deposits - Department of Industrial Engineering, Rapid Prototyping Center, University of Louisville, Louisville, KY 20292, USA HP Labs, 1501 Page Mill Road, Palo Alto, CA 94304, USA 1 Introduction Additive manufacturing belongs to the group of manufacturing technologies where 3D parts are fabricated by material addition in a layer-by-layer fashion, usually from a computer-aided design model [ 1 ]. Additive manufacturing technologies offer enhanced design capabilities for geometric freedom that allows producing parts which are otherwise not possible to fabricate with traditional manufacturing processes. There are various additive manufacturing processes such as selective laser melting, direct laser deposition, electron beam melting, wire-feed additive manufacturing, shape deposition modeling, ultrasonic consolidation, binder jetting, and friction freeform fabrication for producing metallic components [ 1–8 ]. Titanium alloys are used in several structural applications due to their lower density, high strength to weight ratio, corrosion resistance, and elevated temperature properties [9]. Traditionally, titanium alloys are made by vacuum induction re-melting and carefully controlled thermo-mechanical processing to tune the microstructure that will demonstrate satisfactory mechanical properties. Although manufacturing methods are well established for titanium alloys, the high production cost limits the use of these alloys. Additive manufacturing could provide a means to fabricate parts in titanium alloys at a lower cost. Among the various grades of titanium alloys, Ti-6Al-4V (α + β alloy) is the most popular and finds its applications in aerospace, automotive, biomedical, defence and industrial sectors [ 9, 10 ]. The alloy has good weldability characteristics, making it amenable for SLM. Of the commercially available additive manufacturing technologies, selective laser melting (SLM) is one of the most popular and successful powder-bed fusion based additive manufacturing processes. In SLM, consolidation of metal powder is achieved by melting and solidifying a small volume of material in a track-by-track and layer-bylayer fashion using a high-intensity laser. In other words, the laser beam scans over a layer of powder in a straight line and melts the powder particles under the beam and creates a small molten pool of metal. As the laser beam traverses, it leaves a thin track of solidified metal behind. On repeating the single track deposit with a well-defined overlap (hatch spacing), a layer of cross-section is produced. Upon repeating this layer-by-layer deposition, an entire part is constructed [ 1 ]. A simple schematic of the SLM process showing track-by-track and layer-by-layer deposition is presented in Fig. 1 [ 11 ]. SLM is controlled by various processing parameters such as laser power (P), scanning speed (v), layer thickness (t) and hatch spacing (h). These parameters define energy density of the process as [ 12 ]: E ¼ v P h t : Although energy density is a measure of the energy input to the process, there are other factors such as the composition of the metal, atmosphere used, scan pattern, and (...truncated)