Effect of the Melt Pool Boundary Network on the Anisotropic Mechanical Properties of Selective Laser Melted 304L

Myranda Spratt,Okanmisope Fashanu,K Chandrashekhara,Joseph W Newkirk

doi:10.3390/jmmp5040110

Myranda Spratt, Okanmisope Fashanu + Show 2 more

Open Access

https://doi.org/10.3390/jmmp5040110

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Abstract

Anisotropic mechanical properties are a well-known issue in selective laser melted parts. The microstructure produced by selective laser melting (SLM) is directional, including the solidified melt pool structures and grains. This work investigates the melt pool boundary’s effects on 304L stainless steel’s compressive properties. 304L stainless steel solid cylinders were built using a pulse laser SLM machine in four directions using three hatch angle rotations: 0°, 67°, and 105°. The twelve samples were compression tested, and the results were analyzed. Numerical models were also created with the different hatch angles and directions. The melt pool boundary network (MPBN) in each build was tracked using the model across multiple planes. Results showed that both the hatch angle and build orientation influenced the concentration of melt pool boundaries present in the manufactured samples. A weak negative correlation of compressive strength to the melt pool boundaries’ concentration was also observed, indicating that the melt pool boundary concentration negatively affected the material’s strength. Local anisotropic plastic deformation was also observed in some of the compressed samples. In those samples, it was observed that directions that plastically deformed more also contained higher concentration of the melt pool boundaries.

Highlights

Additive manufacturing (AM) has continued to gain increasing interest over the past few years
The Archimedes results were not tabulated as no significant difference was observed with respect to changes to the hatch angle and build orientation
Samples built with hatch angle 67◦ in the [001] direction had the lowest aspect ratio, while samples built with hatch angle 105◦ in the [010] direction had the lowest aspect ratio

Summary

Introduction

Additive manufacturing (AM) has continued to gain increasing interest over the past few years. The build orientation and the laser scan pattern are notable process parameters that influence anisotropic properties This is due to the influence these process parameters have on the microstructure of SLM materials [7,9]. The build orientation, the orientation of the part on the build plate, is usually changed between parts These parameters determine the melt pool patterns formed in the manufactured material. Mower and Long concluded that the low fatigue strength and planar fracture of their 316L samples was a result of the weak ‘build plane’ This theory was used to explain the fracture behavior seen by Wen et al [12] as the crack path appeared to follow the MPBs, rather than the grain boundaries. The relationship between the melt pool boundary concentration, the compressive yield strength, and plastic deformation was estimated using the experimental results and the numerical predictions

Manufacturing and Experimental Testing

Experiments

Modeling of the MPBN

Conclusions