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U.S. ARMY COMBAT CAPABILITIES DEVELOPMENT COMMAND – ARMY RESEARCH LABORATORY

Effects of atomization gas on 17-4 PH StainlessSteel build properties

Frank Kellogg1, Andelle Kudzal2, Josh Taggart-Scarff1, Ryan Rogers3, Brandon McWilliams21Survice Engineering, Belcamp MD2CCDC Army Research Laboratory, APG MD3Bowhead Science and Technology, Belcamp MD

RAMP-MD 2019 Metals Additive Manufacturing Symposium, Bel Air Md,May 2019

Distribution A, cleared for public release

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• Army needs:• Manufacturing at the point of need• Hard to find legacy parts• Decrease long lead times• Design on Demand• Small quantities without need to restart major production

• ARL capabilities:• Open architecture manufacturing equipment• DMLS: ProX 100, ProX300, ProX320, EOS M100• E-beam : Arcam A2X• DED : RPM 222• Lab scale gas atomizer• Powder characterization:

• Morphology and size: Horiba LDA, Camsizer 2• Powder rheology: Brookfield PFT610

INTRODUCTION

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17-4 PH STAINLESS STEEL

• Martensitic, precipitation hardened stainless steel • Combination of common use, high mechanical strength and readily

available powder make AM 17-4 a good candidate material for in-field part replacement

Element Content (%)Iron, Fe 73

Chromium, Cr 15.0 - 17.5Nickel, Ni 3.0 - 5.0

Copper, Cu 3.0 - 5.0Manganese, Mn 1.0

Silicon, Si 1.0Tantalum, Ta 0.45Niobium, Nb 0.45

Nb + Ta 0.15 - 0.45Carbon, C 0.070

Phosphorous, P 0.040Sulfur, S 0.030

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LASER PROCESSING PARAMETERS

Image from 3dsystems.com

PROX DMP 100

• AM Processing Parameters

• Laser Power : 49 W

• Laser Scan Speed : 140 mm/s

• Hatch Spacing : 0.07 mm

• Powder Layer Thickness : 0.03 mm

• Powder: 2 batches

• Commercially available

• 1 batch atomized in N2

• 1 batch atomized in Ar

This project: a summarization of experiments examining how atomization gas changes build properties.

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BACKGROUND

Figures from “Welding Metallurgy and Weldability of Stainless Steels” by John Lippold and Damian Kotecki (originally from ASM Metals Handbook (8th Ed, Vol 8, p 291) via Hansen, 1958, Constitution of Binary Alloys, 2nd Ed and via Baerlacken et al. 1958, “Investigations concerning the transformation behavior, notched impact toughness, and susceptibility to intercrystalline corrosion of iron-chromium alloys with chromium contents to 30%”, Stahl un Eisen, 81 (12)

• Fe-Cr phase diagram• Gamma loop

• Austenite stability window enlarges due to N2• Atomization in nitrogen stabilizes austenite, creates retained

austenite in as-manufactured parts

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CHARACTERIZATION

• XRD starting powders

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CHARACTERIZATION

• XRD after AM

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MICROSCOPY: ARGON ATOMIZED, AS-BUILT

400 µm 100 µm

50 µm 10 µm

XY

AM Melt pool boundaries

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MICROSCOPY: N2 ATOMIZED, AS-BUILT

400 µm 100 µm

50 µm 10 µm

XY

AM Melt pool boundaries

Austenite rich

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• N2 atomized powder used in as-built parts leads to higher strength and hardness but lower ductility and elongation

MECHANICAL PROPERTIES

N2 Gas Atomized

Ar Gas Atomized

N2 Gas Atomized

Ar Gas Atomized

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• 6 mm diameter• 120 mm length wrought samples• 90 mm length AM samples • HAZ Lengths

• Wrought: 39.73 mm• N2 AM: 26.8 mm• Ar AM: 25.47 mm

HAZ SIMULATION

Build ( Z )Direction:

• Gleeble simulation of welding to see:• If AM 17-4 has the same degree of weldability as

wrought 17-4 • Effects of atomization gas

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MICROSCOPY: WROUGHT, POST HAZ

50 µm 10 µm

50 µm 10 µm

Hot End

Cold End

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MICROSCOPY: ARGON POWDER BUILD, POST HAZ

50 µm 10 µm

50 µm 10 µm

Hot End

Cold End

XZ

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MICROSCOPY: N2 POWDER BUILD, POST HAZ

50 µm 10 µm

50 µm 10 µm

Hot End

Cold End

XZ

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DELTA FERRITE

Figure 2.3b from “Welding Metallurgy and Weldability of Stainless Steels” by John Lippold and Damian Kotecki (originally from Castro and Tricot, 1962, “Études des transformations isothermes dans les aciers inoxydables semi-ferritiques á 17% de chrome, Memoires Scientifiques de la Revue de Metallurgie, Part 1: 59:571-586, Part 2, 59: 587-596.)

• Formation of δ ferrite• Fe-Cr-C pseudobinary diagram at 17% Cr

• C1 is a (Cr, Fe)23C6 carbide

• δ ferrite can prevent solidification cracking during welding• Also can lead to embrittlement, lower mechanical properties, and worse

corrosion prevention• Often heat treated out after welding

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• Atomization gas influences mechanical properties, microstructures, and weld behavior• Neither good nor bad:

• Proper heat treatments• Design around properties• Design for implementation (welding?)

• N2 atomized powder leads to parts with:• Higher UTS• Higher hardness• Less δ ferrite after welding

• Ar atomized powder leads to parts with:• Higher ductility• Single phase microstructure

• Need to know entire history of the powder before building

CONCLUSIONS

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ACKNOWLEDGEMENTS

The research reported in this document was performed in connection with contract/instrument W911QX-16-D-0014 with the U.S. Army Research Laboratory. The views and conclusions contained in this document are those of SURVICE Engineering and the U.S. Army Research Laboratory. Citation of manufacturer's or trade names does not constitute an official endorsement or approval of the use thereof. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation hereon.

The research reported in this document was performed in connection with contract/instrument W911QX-17-C-0021 with the U.S. Army Research Laboratory. The views and conclusions contained in this document are those of Bowhead Science and Technology and the U.S. Army Research Laboratory. Citation of manufacturer's or trade names does not constitute an official endorsement or approval of the use thereof. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation hereon.