Effect of Solution Annealing on Plasma Weld Deposited Ti-6Al-4V Characterized by In-Situ Tensile

119 Pages·2014·8.98 MB·English

by  Erlend Næss Trøan

Effect of Solution Annealing on Plasma
Weld Deposited Ti-6Al-4V Characterized
by In-Situ Tensile Testing Combined With
EBSD
Erlend Næss Trøan
Materials Science and Engineering
Submission date: June 2014
Supervisor: Ola Jensrud, IMTE
Co-supervisor: Jarle Hjelen, IMT
Martin Borlaug Mathisen, Norsk Titanium
Norwegian University of Science and Technology
Department of Materials Science and Engineering

Preface
This work has been carried out at the Norwegian Univeristy of Science and Technology (NTNU),
at the Department of Materials Science and engineering, as a master thesis within Material
development and properties.
I would like to express my gratitude to my supervisor Ola Jensrud for very good guidance
throughout the duration of this project. I would also like to thank my co-supervisor Jarle Hjelen,
for many productive talks. In addition, my sincere thanks goes to my company contact at Norsk
Titanium, Martin Borlaug Mathisen, for very helpful guidance along the way.

Trondheim, June 2014
Erlend Næss Trøan

i
ii
Acknowledgements
My sincere thanks go out to the following persons who have guided and helped me throughout
the work of my master thesis.
Ola Jensrud (NTNU) Supervisor
Jarle Hjelen (NTNU) Co-supervisor
Martin Borlaug Mathisen (NTi) Company Supervisor
Yingda Yu (IMT) Engineer at SEM lab
Trygve Schanche (NTNU) Labassistant
Torild Krogstad (NTNU) Labassistant
Robert Karlsen (NTNU) Cutting of samples
Knut Erik Snilsberg (SINTEF) Working with titanium at SINTEF Raufoss Manufacturing
Rene de Kloe (EDAX) Engineer in EDAX (producer of OIM Analysis)
Eli Beate Larsen (NTNU) Dilatometer
Delphine Leroy (NTNU) ReSiNa furnace
Wilhelm Dall (SINTEF) Senior engineer at SINTEF
Astrid Salvesen (NTNU) Coordinator at the glassblowing workshop

I would also like to dedicate my thanks to Norsk Titanium and SINTEF Raufoss Manufacturing for
supplying material and data related to the process and tensile test.

iii
iv
Abbreviations list
AC Air-cooled
AM Additive manufacturing
BCC Body centered cubic
BOR Burgers orientation relationship
CAD Computer aided design
CI Confidence index
CP Commericially pure
CRSS Critical resolved shear stress
EBSD Electron backscatter diffraction
FC Furnace-cooled
HCP Hexagonal close packed
IPF Inverse pole figure
IQ Image quality
NTi Norsk Titanium
ROI Region of interest
SE Seconday electrons
SEM Scanning electron microscope
SiC Silicon carbide
TEM Transmission electron microscope
v
vi
Abstract
This work is based on the work done by Mathisen et al. [1], which considers the mechanical
properties of the components produced by Norsk Titanium (NTi). NTi produces Ti-6Al-4V (grade
5 titanium) components by additive manufacturing (AM). After receiving samples from NTi, the
material were heat-treated in order to study the possible differences in deformation mechanisms.
The material was either furnace-cooled (FC) or air-cooled (AC) after solution annealing at 950°C
for 1 hour. Both FC and AC samples went to an aging procedure at 600°C for two hours after
solution annealing. The deformation mechanisms were observed by doing in-situ tensile tests
with electron-backscattered diffraction (EBSD). The time spent on sample preparation for EBSD
proved valuable as the average CI-, fit- and IQ-values for the tensile specimens before
deformation were 0.44, 1.07 and 144.8 respectively.
Both prismatic and basal slip are present in the material, in addition to hard/soft-grain
deformation. The combination of elastic stiffness and Schmid factor proved effective for
calculating the activation and propagation of all three types of deformation. In the as-received
material, the deformation accumulates at the columnar β-grain boundaries, while after heat
treatment, the deformation are more uniformly distributed among the β-grains. The anisotropy
of the material is however still obvious, as the deformation is concentrated in certain grain.
The AC material gained a more homogenous width of α-lamellas as compared to the as-received
material, although tendencies towards basketweave structure were still present. The FC material
obtained α-lamellae that are more discontinuous than in the as-received material. The larger the
width of the α-lamellas, the higher the ductility, as slip can propagate longer. If the slip isn’t
restricted by the orientation of the neighboring lamellas, the material can travel even further.
Due to a strict orientation relationship, the material doesn’t seem to obtain a more isotropic
texture after the heat treatment. Due to a non-equilibrium composition and microstructure in the
AM material, the use of dilatometry was unable to obtain any useful data to determine the
transition temperature. The first specimens that underwent a heat treatment showed a very
brittle behavior, as the material had been exposed to a contamination of both hydrogen and
oxygen. This underlines the importance of atmospheric protection when operating with titanium
at elevated temperatures.
vii
viii