Abstract
This research aims to identify how meltpool temperature is determined by process parameters in Laser-Based Powder Bed Fusion (LB-PBF) and the effect of meltpool temperature and heat treatment temperature on microstructure and tensile properties. The study illustrates how crystallographic features in 316L stainless steel were developed in response to the meltpool temperature and induced energy density of LB-PBF manufacture, and by post manufacture heat treatment. For this research, 25 samples based on a Taguchi Design of Experiments (DoE) with five parameters over five levels were printed. To improve precision, the DoE was repeated three times and a total of 75 samples were produced. A thermophysical-based analytical model was developed to measure the meltpool temperature and subsequently surface tension of the liquid in melting zones. Then, a statistical method was used to identify the effective process parameters in tensile properties including ultimate strength, fracture strain and toughness. The microstructural evaluation and crystallographic features were presented to identify the governing mechanisms for the discussed phenomena. This result verifies that the meltpool temperature is a driving factor for the microstructural evolution and observed crystallographic features. Results showed that samples with lower meltpool temperatures have smaller grain sizes, superior strength and toughness properties. The crystallographic analysis showed the weak texture and anisotropic properties are dominant by the preferred orientation growth. The geometrically necessary boundary values were also found to be a driving factor for fracture strain. The originality of this paper is identifying the effect of process parameters on meltpool temperature using an analytical model that is developed based on the thermophysical properties of the feedstock. Characterizing the effect of meltpool temperature in crystallographic features are also another contribution of this paper.
Highlights
Laser-Based Powder Bed Fusion (LB-PBF) is a classification of additive manufacturing whereby a highly energized laser beam fuses metallic powder in subsequent layers for the manufacture of complex structures directly from computeraided design (CAD) data [1e3]
Different investigations have been conducted on the effect of process parameters on parts manufactured by the LB-PBF process and they showed that parameters like point distance, laser power and scan speed have a strong effect on the observed mechanical properties [7e10]
The results showed that less than 1% error with the literature [40], which demonstrates the accuracy of the performed analysis
Summary
Laser-Based Powder Bed Fusion (LB-PBF) is a classification of additive manufacturing whereby a highly energized laser beam fuses metallic powder in subsequent layers for the manufacture of complex structures directly from computeraided design (CAD) data [1e3]. Stainless Steel (SS) 316L can replace expensive materials like aluminium and titanium as a more cost-efficient alternative for automotive application It has robust mechanical properties and excellent corrosion resistance [4e6]. Increasing the energy density causes an exponential decrease in porosity and a linear increase in hardness [8] Another technical challenge of LB-PBF is the surface roughness caused by the balling effect, which is more evident in materials with high thermal conductivity [11,12]. During metallic 3D printing, porosity formation is negligibly affected by the part orientation and gas flow condition These two factors considerably affect the thermal stress and bonding strength, which are critical to the observed mechanical properties of a printed part [17]
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