PSI - Issue 46

David Liović et al. / Procedia Structural Integrity 46 (2023) 42 – 48

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D. Liovi ć et al. / Structural Integrity Procedia 00 (2019) 000–000

1. Introduction The possibility to influence microstructure, surface morphology, and thus mechanical properties of the metallic materials by applying different selective laser melting (SLM) process parameters, arise great interest in fields where high topological complexity, reduced mass and high mechanical properties are often required as Kotzem et al. (2021), Shi et al. (2021), Tallon et al. (2020) and Viespoli et al. (2020) have shown. Applying SLM as one of the widely used and fast-growing powder bed fusion technologies provides a potential solution to this demanding task. Numerous SLM process parameters can affect microstructure, surface morphology, mechanical properties, and overall product quality, but the two most important parameters are laser power and scanning speed according to Kasperovich et al. (2016). Usually, when defining the optimal combination of process parameters, researchers are guided by the principle of minimizing porosity, and thus stabilizing the SLM process, since in this way the mechanical properties of additively manufactured materials can be significantly improved. As result, a significant step forward was made in understanding the influence of individual process parameters, as well as their interactions on monotonic and low cycle fatigue behavior. Therefore, further improvements in the mechanical properties of additively manufactured materials needs to be directed to the study of the influence of different process parameter combinations on mechanical performance, by maintaining nearly full density for each combination. On the example of SLM-ed Ti6Al4V alloy, even for the same porosity fractions, significant differences in elongation at break values can be present. Therefore, the shape, type and volume of porosity are not the only harmful factors that contribute to lowering the mechanical properties of additively manufactured metallic materials. It was found that the size and orientation of prior β-grain boundaries, as well as different types of acicular martensite formed by heating cycles specific to the SLM process, also have an influence on mechanical performance of SLM-ed Ti6Al4V alloy as Pal et al. (2019) demonstrated. The primary goal of this work is to extend previous research findings of the influence of laser power and scanning speed on the microstructure, surface morphology, and monotonic mechanical properties of SLM-ed Ti6Al4V alloy. Furthermore, the secondary goal of this study is devoted to manufacturing nearly full dense material using process parameters stated in this paper, which is a mandatory step for further improvements of mechanical performance and overall product quality of SLM-ed components. 2. Materials and methods 2.1. SLM and heat treatment process parameters Both tensile test specimens and cubic specimens were manufactured using spherical Ti6Al4V ELI powder with particle size between 6.5 μm to 80 μm in diameter using Concept Laser M2 Cusing machine located in LAMA FVG. The SLM machine is equipped with a 400 W single-mode CW ytterbium-doped fiber laser. During SLM the machine chamber was filled with argon gas to keep oxygen level below the 0.2%. Process parameters used in this study for manufacturing of 36 tensile test and 9 cubic specimens are listed in Tab. 1.

Table 1. Used SLM process parameters. SLM process parameters

Levels of variation / constant value

P – laser power (W)

200, 225, 250

v – scanning speed (mm/s) t – layer thickness (mm) h – hatch distance (mm) d – laser spot diameter (mm)

1000, 1250, 1500

0.025

0.09

0.1

Scanning strategy

Bi-directional, single pass, 90° rotation of scan vector between layers