In-Built Customised Mechanical Failure of 316L Components Fabricated Using Selective Laser Melting

Abstract

Abstract:The layer-by-layer building methodology used within the powder bed process of Selective Laser Melting facilitates control over the degree of melting achieved at every layer. This control can be used to manipulate levels of porosity within each layer, effecting resultant mechanical properties. If specifically controlled, it has the potential to enable customisation of mechanical properties or design of in-built locations of mechanical fracture through strategic void placement across a component, enabling accurate location specific predictions of mechanical failure for fail-safe applications. This investigation examined the process parameter effects on porosity formation and mechanical properties of 316L samples whilst maintaining a constant laser energy density without manipulation of sample geometry. In order to understand the effects of customisation on mechanical properties, samples were manufactured with in-built porosity of up to 3% spanning across~1.7% of a samples' cross-section using a specially developed set of "hybrid" processing parameters. Through strategic placement of porous sections within samples, exact fracture location could be predicted. When mechanically loaded, these customised samples exhibited only~2% reduction in yield strength compared to samples processed using single set parameters. As expected, microscopic analysis revealed that mechanical performance was closely tied to porosity variations in samples, with little or no variation in microstructure observed through parameter variation. The results indicate that there is potential to use SLM for customising mechanical performance over the cross-section of a component.

Processing Parameter Effects on Residual Stress and Mechanical Properties of Selective Laser Melted Ti6Al4V

“…Pohl et al (Ref 10 ) reported lower deformation for higher scan speed. Combined effect of varying power and exposure together keeping energy density constant on porosity and in turn on mechanical properties was studied by Andrei et al (Ref 28 ). For a constant energy density, lower power and higher exposure combination led to an increase in porosity and thus reduction in yield strength of 316L SLM samples (Ref 28 ).…”

Diode area melting single-layer parametric analysis of 316L stainless steel powder

“…It can be seen in Fig. 13a that most of the selected samples showed a~0.2 φ cross-micro (99.8% density) similar to conventional 316L stainless steel SLM parts [13]. The slower 1 mm/s scan speed showed a stable trend of low φ cross-micro whilst the higher 3 mm/s scan speed showed a high rate of decreasing φ cross-micro from~1.4 to~0.2% at increasing laser power.…”

“…This can be attributed to the continuous overlapping of laser spots creating a continuous melting area comprised by smaller melting spots. However, Ilie et al [13] report that porosity in stainless steel samples can vary when varying laser power or scanning velocity at same energy densities due to lack of fusion, Rayleigh instability, balling or poor wetting characteristics as detailed by Rombouts et al [14]. Decreasing levels of porosity were observed for LBP2 when scanned at 1 mm/s compared to the higher laser traversing speeds of 3 and 5 mm/s.…”

Effect of pre-emptive in situ parameter modification on residual stress distributions within selective laser-melted Ti6Al4V components

“…Higher scan speed leads to increased cooling rate and increased cracking [32], while Pohl et al [24] reported lower deformation for higher scan speed. Lower power and higher exposure combination (for constant energy density) lead to increased porosity and thus reduced yield strength in 316-L SLM samples [33]. Ali et al [34] reported lower residual stress for lower power and higher exposure combination (for constant energy density).…”