Influence of process parameters on the final 316L stainless steel properties manufactured by selective laser melting (SLM)

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Influence of process parameters on the final 316L

stainless steel properties manufactured by selective laser

melting (SLM)

A. Chniouel, F. Lomello, P. Giroux, P. Aubry, H. Maskrot

To cite this version:

A. Chniouel, F. Lomello, P. Giroux, P. Aubry, H. Maskrot. Influence of process parameters on the final 316L stainless steel properties manufactured by selective laser melting (SLM). Euromat2017, Sep 2017, Thessalonique, Greece. �cea-02417316�

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INFLUENCE OF PROCESS

PARAMETERS ON THE FINAL

316L STAINLESS STEEL

PROPERTIES MANUFACTURED

BY SELECTIVE LASER MELTING

(SLM)

| PAGE 1 CEA | 10 AVRIL 2012

A. CHNIOUEL

a*

_{, Dr F. LOMELLO}

a

_,

Dr P.F. GIROUX

b

_{, Dr P. AUBRY}

a

_,

Dr H. MASKROT

a

a_{DEN – Service d’Etudes Analytiques et de Réactivité des Surfaces (SEARS), CEA,}

Université Paris-Saclay, F-91191, Gif sur Yvette, France.

b_{DEN – Service de Recherches Métallurgiques Appliquées (SRMA), CEA, Université}

Paris-Saclay, F-91191, Gif sur Yvette, France

*Corresponding author E-mail adress: aziz.chniouel@cea.fr

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Additive Manufacturing: growing technology in the industrial world for different sectors: aeronautics

– automotive –

medicine.



Nuclear industry? Exploring by DOE (U.S.A) since 2012 for different materials: IN600, IN718, IN800,

316L SS, ODS steels.



Benefits:



Complex manufacturing of geometrical parts for nuclear applications.



Components manufacturing which are impossible to process by others traditional processes (cast, forge,

rolling,…).



Processing steps reduction depending on parts complexity (i.e. GE-SAFRAN Leap-X fuel injector).



Waste reduction: powder recyclability.



Rapid prototyping.



Question: Is additive manufacturing adapted for producing nuclear components? (GEN IV

– Sodium Fast

Cooled Reactor).

 Material: 316L SS.

 Mechanical, corrosion and irradiation properties ?

 Understand relation between process and microstructure.

The influence of

substrate temperature

on the

microstructure

and

mechanical properties of 316L SS samples

INTRODUCTION: CONTEXT

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OUTLINE

26 SEPTEMBRE 2017 | PAGE 3

Raw material properties: 316 SS

powder

Experimental details

Influence of the processes parameters

on the samples properties

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 Chemical composition

 Particles size

26 SEPTEMBRE 2017 _{| PAGE 4}

Majority elements by ICP-OES (% wt) (uncertainly related of 3%) Minority elements (%wt)

By GDOES and LECO (uncertainly related of 5%)

Cr Ni Mn Si Mo C N O S P Standard RCC-MRx 16,5-18,50 10-13 2 max 1 max 2-2,5 300 max 1100 max -150 max 300 max 316L SS powder 17,35 11,45 1,06 0,51 2,07 230 982 1876 130 305 0,0 10,0 20,0 30,0 40,0 50,0 60,0 70,0 80,0 90,0 100,0 0,0 5,0 10,0 15,0 20,0 25,0 30,0 17 20 23 26 30 34 39 45 51 59 68 77 89 101 Cumulative frequency, % Frequency, % Particle Size (µm)

Frequency distribution

D₁₀ 29 µm D50 38 µm D90 51 µm

316L SS POWDER PROVIDED BY SLM SOLUTIONS

 Chemical composition in good agreement with RCC-MRx Code  French Nuclear

Standard for Experimental Reactors

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 Argon atomized powder.

 Typical heterogeneous shapes.

316L SS POWDER PROVIDED BY SLM SOLUTIONS

 Satellites

 Rod-like particles

 Morphology

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OUTLINE

Raw material properties: 316 SS

powder

Experimental details

Influence of the processes parameters

on the samples properties

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EXPERIMENTAL PROCESS: SELECTIVE LASER

MELTING

| PAGE 7



Fixed process parameters:

 Power: 175W

 Layer thickness, e=30 µm  Scan speed, v=700 mm/s  Hatching distance, HD: 100 µm

 Argon gas atmosphere.  Scan Strategy:

incrementation of 67° between each layer



Variable process parameter:



Heating Platform

RT=25°C < T < 600°C

SLM 280HL

Selective laser melting Power max: 400 W

Ytterbium doped laser fiber. Laser’s spot size: 75 µm

E=

_{𝑒.𝑣.𝐻𝐷}𝑃

= 84 J/mm

3

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1cm

EXPERIMENTAL PROCESS: SELECTIVE LASER

MELTING

26 SEPTEMBRE 2017

| PAGE 8

Substrate Samples

 Build enveloppe size: Ø=100 mm and height 100 mm.

 Aim: reduce thermal stresses and formation of cracks in the parts. Laser system Argon Recoater Overflow Part Substrate Thermocouple Ceramic substrate

Flow diagram

BD

 Samples manufactured at different temperatures:  RT, 100°C, 200°C, 350°C, 500°C and 600°C.

 Cylindrical and Beam-like samples (X, Y, Z and 45° from XY plane).

Aim of In situ heat:

Decrease internal thermal stresses.

Grain sizes modification.



“In situ” heat treatment in order to

reduce post process steps.

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OUTLINE

Experimental details

Raw material properties: 316 SS

powder

Influence of processes parameters on

the samples properties

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600°C

200°C

BD

Top

MICROSTRUCTURE

MECHANICAL PROPERTIES

Micro scale: Grains

Bottom

 Columnar grains along B.D.: length around 4

times width.

 Grains grow across layers (30 µm).

 Grains are more elongated at 600°C on the

BOTTOM (L=220 µm)

 Grains size influenced by the substrate

temperature (Temperature higher at the

bottom).

 No influence of temperature on grains width.

EBSD grains cartography

0 20 40 60 80 100 120 140 160 180 200 220 240 200 350 600 Average grain size (µm) Substrate Temperature (°C) Length BOTTOM Length TOP width BOTTOM Width TOP 300 µm 300 µm 300 µm 300 µm | PAGE 10

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Micro scale: Grains

 No significant influence of the

substrate temperature on the

cells size:

 intra

granular

cells

size

between 0.6 and 1 µm.

 High cooling rate (10

3

_-10

6

K/s) -

Casati and al. Journal of

Meterials Science and Technology

,2016, 32: 738-744

 Inside a same grain: (grain 2)

Direction

of

growth

of

S/L

interface can vary from one melt

pool to another

– Mertens and al.,

Materials Science, 2011, 783-786,

898-903

Melt pool boundary

Grain boundary

Substrate temperature

350 °C

Grain 1 Grain 2 Grain 3

Intra granular cells

MICROSTRUCTURE

10 µm

3 µm

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Nano scale: Precipitates

| PAGE 12

 Analyse at the middle of the sample

height (4.5 cm).

 No influence of the substrate

temperature on:

 Structure: amorphous.

 Shape: spherical.

 Size: diameter ranging 10 to

170 nm.

 Composition: O, Si, Mn.

 Trace of S, Mo and Al in some

precipitates.

 Nano oxydes formation in situ during the build process  improve mechanical properties - K. Saeidi Ph. D. Thesis (2016).

 Precipitates size and density are highly influenced by the oxygen content in the build chamber - Zhou et al. Mater. Sci. Eng., 2017, 167.

 Nano precipitates can improve swelling resistance under neutron irradiation- Sun et al., Sci. Rep., 2015, 5, 7801.

Sun et al. Sci. Rep., 5, 2015, 7801 Zhong et al.

J. Nucl. Mat. 470, 2016, 170

MICROSTRUCTURE

Nano precipitates 316L STEM BF Substrate Temperature 350°C STEM BF Substrate Temperature 600°C 200 nm 200 nm 1 µm

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| PAGE 13

■

▲

♦

●

HV1 10-25 25-40 _50-65 _65-80 Sample height (mm)

 Microhardness along building direction, Z direction.

 No influence of the height on microhardness for RT, 200°C and 350°C.

 At 600°C, microhardness increases linearly according to sample height.  Grains more columnar (Hall Petch effect)

 Internal stresses relieved on the BOTTOM  Thermal gradient.

 Same values reported by Zhong:

Zhong et al. J. Nucl. Mat. 470 (2016) 170.

Micro Hardness

 Microhardness decreases as a function of temperature.

 Same trend observed after heat treatment -Herliansyah and al., Proceedings, 2015.

210 215 220 225 230 235 240 RT 200°C 350°C 600°C HV1 Substrate Temperature (°C) 15-25 mm10-25 mm 25-40 mm 50-65 mm 65-80 mm RT 200°C 350°C 600°C

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Tensile test

Samples manufactured along B.D.

Influence of the substrate temperature

622 616 599 595 584 520 540 560 580 600 620 RT 200°C 350 °C 500 °C 600 °C UTS (MPa) Substrate temperature

Ultimate strength

525 526 491 463 ₄₅₄ 220 280 340 400 460 520 580 RT 200°C 350 °C 500 °C 600 °C σ0.2 (MPa) Substrate temperature

Yield strength

47 48 49 49 53 42 44 46 48 50 52 54 RT 200°C 350 °C 500 °C 600 °C (%) Substrate temperature

Elongation

 Samples machined according the ISO 6892-1 standard.  Test at room temperature.

 Strength and Yield strength decrease linearly as a function of temperature.  Similar trend followed by the microhardness.

 Same trend observed after heat treatment:

 Mechanical properties respect the minimum requirement of the nuclear standard.

Grains are more columnar along building

direction when temperature increases.

Dislocation / Internal stresses relieved ?

MICROSTRUCTURE

MECHANICAL PROPERTIES

Forged 316LSS, RCC-MRx France nuclear Standard

| PAGE 14

 Elongation increases linearly as a function of temperature.

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