Powder Characterization for Additive Manufacturing Processes

128 Pages·2017·6.2 MB·English

Powder Characterization for Additive
Manufacturing Processes
Lisa Markusson
Materials Engineering, masters level
2017
Luleå University of Technology
Department of Engineering Sciences and Mathematics
Preface
This master thesis work has been carried out at GKN Aerospace Engine Systems Sweden at
the Department of Process Engineering in Trollhättan, Sweden. This is a degree project in
engineering materials performed as the final part of my Masters of Materials Sciences and
Engineering degree.
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To my grandparents

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Abstract
The aim of this master thesis project was to statistically correlate various powder
characteristics to the quality of additively manufactured parts. An additional goal of this
project was to find a potential second source supplier of powder for GKN Aerospace Sweden
in Trollhättan. Five Inconel® alloy 718 powders from four individual powder suppliers have
been analyzed in this project regarding powder characteristics such as: morphology, porosity,
size distribution, flowability and bulk properties. One powder out of the five, Powder C, is
currently used in production at GKN and functions as a reference. The five powders were
additively manufactured by the process of laser metal deposition according to a pre-
programmed model utilized at GKN Aerospace Sweden in Trollhättan. Five plates were
produced per powder and each cut to obtain three area sections to analyze, giving a total of
fifteen area sections per powder. The quality of deposited parts was assessed by means of
their porosity content, powder efficiency, geometry and microstructure. The final step was to
statistically evaluate the results through the analysis methods of Analysis of Variance
(ANOVA) and simple linear regression with the software Minitab.
The method of ANOVA found a statistical significant difference between the five powders
regarding their experimental results. This made it possible to compare the five powders
against each other. Statistical correlations by simple linear regression analysis were found
between various powder characteristics and quality of deposited part. This led to the
conclusion that GKN should consider additions to current powder material specification by
powder characteristics such as: particle morphology, powder porosity and flowability
measurements by a rheometer.
One powder was found to have the potential of becoming a second source supplier to GKN,
namely Powder A. Powder A had overall good powder properties such as smooth and
spherical particles, high particle density at 99,94% and good flowability. The deposited parts
with Powder A also showed the lowest amount of pores compared to Powder C, a total of 78
in all five plates, and sufficient powder efficiency at 81,6%.

Keywords: Powder Characteristics, Inconel 718, Additive Manufacturing, Laser Metal
Deposition, ANOVA, Regression Analysis

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Sammanfattning
Syftet med detta examensarbete var att statistiskt korrelera olika pulveregenskaper med
kvaliteten på additivt tillverkade delar. Ett vidare syfte med projektet var att finna en
potentiell andrahandsleverantör av pulver för GKN Aerospace Sweden i Trollhättan. Fem
pulver av materialet Inconel® 718 från fyra individuella pulverleverantörer har analyserats i
detta projekt gällande pulveregenskaper såsom: morfologi, porositet, storleksfördelning,
flytbarhet och bulkegenskaper. Ett pulver av de fem, Pulver C, används för nuvarande
produktion på GKN och fungerar som en referens. De fem pulvren har additivt tillverkats
enligt en förprogrammerad modell, framtagen på GKN Aerospace Sweden i Trollhättan,
genom processen ’laser metal deposition’. Fem provplåtar producerades per pulver och
provbereddes för att erhålla tre ytor för vidare analys, totalt femton ytor per pulver. Kvaliteten
på deponerat material bedömdes utifrån dess porositet, verkningsgrad av pulver, geometri och
mikrostruktur. Det slutliga steget var en statistisk analys av resultaten genom metoderna
Analysis of Variance (ANOVA) och enkel linjär regression med mjukvaran Minitab.
Metoden enligt ANOVA fann en statistisk signifikant skillnad mellan de fem pulvren
gällande dess egenskaper och experimentella resultat. Detta gjorde det möjligt att kunna
jämföra de fem pulvren mot varandra. Statistiska samband utifrån en enkel linjär
regressionsanalys erhölls mellan olika pulveregenskaper och kvalitativa resultat av deponerat
material. Detta ledde till slutsatsen att GKN bör överväga tillägg till nuvarande
pulvermaterialspecifikation med pulveregenskaper såsom: partikelmorfologi, pulverporositet
och flytbarhet genom mätningar av en reometer.
Ett pulver bedöms ha potential att bli en andrahandsleverantör till GKN Aerospace, nämligen
Powder A. Pulver A hade övergripande goda pulveregenskaper såsom jämna och sfäriska
partiklar, hög partikeltäthet på 99,94% och god flytbarhet. De deponerade proverna med
Pulver A uppvisade även lägst antal porer i jämförelse med Powder C, totalt 78 porer i alla
fem provplåtar, och godkänd pulververkningsgrad på 81,6%.

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Acknowledgements
I would like to give my deepest gratitude to my supervisors during this master thesis project;
Lars Östergren at GKN Aerospace Sweden in Trollhättan and Marta-Lena Antti at Luleå
University of Technology. Their great knowledge and guidance have brought this project to
its best. Special thanks also goes to Jimmy Johansson at GKN Aerospace Sweden for sharing
his expertise throughout this master thesis project. The operators at GKN who produced the
experimental samples must not be forgotten and I thank you for the help and support. A final
acknowledgement for the staff at the Department of Process Engineering at GKN for making
these past months filled with laughter and new experience. Thank you.

Trollhättan, March 2017

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Table of Contents
1 Introduction..................................................................................................................... 1
1.1 Collaborate Company Presentation .......................................................................... 1
1.2 Background .............................................................................................................. 1
1.3 Goal .......................................................................................................................... 2
1.4 Scope ........................................................................................................................ 2
2 Literature Review ........................................................................................................... 3
2.1 Additive Manufacturing Processes .......................................................................... 3
2.1.1 Process Classifications ........................................................................................ 3
2.1.2 Advantages & Disadvantages .............................................................................. 4
2.2 Laser Metal Deposition with Powder ....................................................................... 6
2.2.1 Basis of Deposition Process ................................................................................ 6
2.2.2 Powder Nozzles & Feeder System ....................................................................... 7
2.2.3 Basic Deposition Geometry ................................................................................. 9
2.2.4 Process Parameters & Their Effect on Deposited Geometry ............................ 10
2.2.5 Heat Transfer, Solidification & Microstructure Characteristics ...................... 10
2.3 Nickel Based Superalloys ...................................................................................... 12
2.3.1 Inconel 718 ........................................................................................................ 13
2.4 Powder Manufacturing Processes .......................................................................... 14
2.4.1 Gas Atomization ................................................................................................ 15
2.4.2 Plasma Atomization ........................................................................................... 16
2.4.3 Plasma Rotation Electrode Process .................................................................. 16
2.5 Powder Characteristics ........................................................................................... 16
2.5.1 Morphology ....................................................................................................... 17
2.5.2 Porosity .............................................................................................................. 17
2.5.3 Size & Size Distribution ..................................................................................... 18
2.5.4 Rheology ............................................................................................................ 19
2.5.5 Bulk Properties .................................................................................................. 21
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2.5.6 Quality Assessment of Powder ........................................................................... 22
2.6 Statistical Significance ........................................................................................... 22
2.6.1 Analysis of Variance .......................................................................................... 22
2.6.2 Regression Analysis ........................................................................................... 24
3 Materials & Methods .................................................................................................... 25
3.1 Powder & Sheet Material ....................................................................................... 25
3.2 Powder Characterization ........................................................................................ 26
3.2.1 Morphology ....................................................................................................... 26
3.2.2 Porosity .............................................................................................................. 27
3.2.3 Particle Size Distribution .................................................................................. 29
3.2.4 Rheology ............................................................................................................ 30
3.2.5 Bulk Properties .................................................................................................. 32
3.3 Laser Metal Deposition .......................................................................................... 33
3.4 Deposit Evaluation ................................................................................................. 34
3.4.1 Sample Preparation ........................................................................................... 34
3.4.2 Defects ............................................................................................................... 34
3.4.3 Geometry ........................................................................................................... 34
3.4.4 Microstructure ................................................................................................... 35
4 Results & Discussions ................................................................................................... 36
4.1 Powder Characterization ........................................................................................ 36
4.1.1 Morphology ....................................................................................................... 36
4.1.2 Porosity .............................................................................................................. 42
4.1.3 Particle Size Distribution .................................................................................. 44
4.1.4 Rheology ............................................................................................................ 49
4.1.5 Bulk Properties .................................................................................................. 53
4.2 Deposit Evaluation ................................................................................................. 54
4.2.1 Powder Efficiency .............................................................................................. 54
4.2.2 Geometry ........................................................................................................... 56
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4.2.3 Defects ............................................................................................................... 59
4.2.4 Microstructure ................................................................................................... 62
4.3 Statistical Evaluation.............................................................................................. 68
4.4 Statistical Correlation ............................................................................................. 76
4.4.1 Median Particle Size – Basic Flow Energy ....................................................... 76
4.4.2 Median Particle Size – Powder Efficiency ........................................................ 79
4.4.3 ShapeFactor – Basic Flow Energy .................................................................... 81
4.4.4 ShapeFactor – Powder Efficiency ..................................................................... 83
4.4.5 Basic Flow Energy – Powder Efficiency ........................................................... 85
4.4.6 Basic Flow Energy – Multi-bead Height ........................................................... 87
4.4.7 Particle Pore Frequency – Deposit Pore Frequency ........................................ 89
4.4.8 Particle Pore Size – Deposit Pore Size .............................................................. 91
5 Conclusions .................................................................................................................... 98
6 Future Work................................................................................................................ 100
7 Bibliography ................................................................................................................ 101
8 Appendix ...................................................................................................................... 106
8.1 Particle Pixel Area Fraction ................................................................................. 106
8.2 Particle Pore Diameter ......................................................................................... 107
8.3 Summary of Pore Data in Powder & Deposited Part ........................................... 108
8.4 Morphology .......................................................................................................... 109
8.5 Rheometer ............................................................................................................ 109
8.6 Part Geometry ...................................................................................................... 110
8.7 Statistical Evaluation............................................................................................ 111

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Abbreviations & Nomenclature

Name Abbreviation

Additive manufacturing AM

Aluminum Al
American society for testing and materials ASTM
Analysis of variance ANOVA

Chromium Cr

Electrode induction melting gas atomization EIGA

Face-centered cubic FCC

Gas atomization GA
General electric GE
Hot isostatic pressing HIP

Iron Fe

Laser metal deposition LMD

Laser metal deposition with powder LMD-p

Nickel Ni
Niobium Nb
Optical microscope OM

Particle size distribution PSD

Plasma Atomization PA

Plasma rotation electrode process PREP
Scanning Electron Microscopy SEM
Tantalum Ta
Three-dimensional 3D

Titanium Ti

Vacuum Inert Gas Atomization VIGA

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