Dr. Tait D. McLouth Profile

Dr. Tait D. McLouth

at Aerospace Corp

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Publications (2)

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Proceedings Article | 4 March 2022 Presentation + Paper

Effect of test temperature and strain rate on elevated temperature tensile tests of Inconel 718 prepared by selective laser melting

Tait McLouth, David Witkin, Julian Lohser, Scott Sitzman, Paul Adams, Glenn Bean, Jenn-Ming Yang, Rafael Zaldivar

Proceedings Volume 11992, 1199205 (2022) https://doi.org/10.1117/12.2613475

KEYWORDS: Oxidation, Heat treatments, Diffusion, Scanning electron microscopy, Additive manufacturing

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This study analyzes the elevated temperature tensile results of SLM IN718 as a function of strain rate and test temperature in order to better understand the temporal and thermal aspects of environmental sensitivity. Fully heat-treated SLM samples are directly compared to wrought material and corresponding industry standards in order to provide a valuable perspective on the current state of SLM capabilities. It is found that SLM material tested across all conditions have inferior strength and ductility compared to wrought material of the same heat treatment. Strength variation is attributed to different sizes of the primary strengthening phase, γ’’, while ductility variation is caused by environmental sensitivity. SLM samples show evidence of brittle intergranular fracture, crack growth, and oxidized NbC particles on the fracture surface. These features are intensified with decreasing strain rate and increasing temperature. EBSD-generated misorientation maps and strain rate sensitivity calculations demonstrate that the mechanism of plastic deformation is similar between the two processing conditions but wrought material has a greater overall damage tolerance. Premature failure attributed to intergranular crack growth leads to poor ductility in SLM material. Faster strain rates and lower temperatures are shown to improve the ductility in SLM IN718 but despite this recovery it remains susceptible to environmental attack even in the extreme cases of the current study. Sources of environmental sensitivity and the degree to which they affect elevated temperature mechanical properties are discussed.

Proceedings Article | 26 February 2018 Paper

The effect of laser focus and process parameters on microstructure and mechanical properties of SLM Inconel 718

Glenn Bean, David Witkin, Tait McLouth, Rafael Zaldivar

Proceedings Volume 10523, 105230Y (2018) https://doi.org/10.1117/12.2299615

KEYWORDS: Surface roughness, Laser processing, Laser energy, Heat treatments, 3D modeling, Additive manufacturing, Nickel, Metals

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Research on the selective laser melting (SLM) method of laser powder bed fusion additive manufacturing (AM) has shown that surface and internal quality of AM parts is directly related to machine settings such as laser energy density, scanning strategies, and atmosphere. To optimize laser parameters for improved component quality, the energy density is typically controlled via laser power, scanning rate, and scanning strategy, but can also be controlled by changing the spot size via laser focal plane shift. Present work being conducted by The Aerospace Corporation was initiated after observing inconsistent build quality of parts printed using OEM-installed settings. Initial builds of Inconel 718 witness geometries using OEM laser parameters were evaluated for surface roughness, density, and porosity while varying energy density via laser focus shift. Based on these results, hardware and laser parameter adjustments were conducted in order to improve build quality and consistency. Tensile testing was also conducted to investigate the effect of build plate location and laser settings on SLM 718. This work has provided insight into the limitations of OEM parameters compared with optimized parameters towards the goal of manufacturing aerospace-grade parts, and has led to the development of a methodology for laser parameter tuning that can be applied to other alloy systems. Additionally, evidence was found that for 718, which derives its strength from post-manufacturing heat treatment, there is a possibility that tensile testing may not be perceptive to defects which would reduce component performance. Ongoing research is being conducted towards identifying appropriate testing and analysis methods for screening and quality assurance.

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