1. INTRODUCTION
Additive manufacturing (AM) is an emerging technology based on “layer-by-layer”
fabrications. AM technology offers many design and manufacturing advantages such
as short lead time, complex geometry capability and tooling free. Electron beam
additive manufacturing (EBAM) is a type of AM technology for the direct manufacturing
of metal products by melting metallic powders. EBAM utilizes a high-energy electron
beam, as a moving heat source, to melt and fuse metal powders and produce parts in
a layer-building fashion. It is of great interest to investigate the possible build heights
effects on microstructure and mechanical properties. Ti-6Al-4V is the most common
titanium alloy used in such industries, the application of EBAM on Ti-6Al-4V achieves
the fine structure and superior mechanical properties.
EXPERIMENTAL DETAILS
Sample Fabrication
Microstructural Characterization
Optical Microscope (OM), Scanning Electron Microscope (SEM)
Nanoindentation
Triboindenter: Berkovich tip (radius of 100 nm, included angle of 142.3 deg.)
POWDERS CHARACTERIATION
Raw Powders: a diameter between 45 and 100 µm
Sintered Powders: connected powders
MICROSTRUCTURES
Side Surfaces (X-plane)
Top layers: straight and fine columnar prior β structure
Middle layers: curved columnar structure
Bottom layers: martensitic structure
Scanning Surface (Z-plane): equiaxed grains and Widmanstätten (α+β)
General Structure: rod-shaped
NANOINDENTATION
CONCLUSIONS
(1) The side surfaces specimens show columnar prior β grains with martensitic
structures. The top layers presents the smallest columnar width.
(2) The scanning surfaces show equiaxed grains. The inside microstructure consists of
fine Widmanstätten (α+β) and α′ martensites.
(3) The highest elastic modulus and hardness are located at the scanning surface of
the top layers. In addition, the elastic modulus and hardness are higher on the
scanning surface than those from the side surface.
ACKNOWLEDGEMENTS
The materials presented in this paper are supported by NASA, under award No.
NNX11AM11A. XG also acknowledges the AL EPSCoR GRSP for the financial support.
MICROSTRUCTURES AND NANOINDENTATION CHARACTERIZATION OF TI-6AL-4V PARTS PROCESSED BY ELECTRON BEAM ADDITIVE MANUFACTURING
ABSTRACT: The microstructure analysis and nanoindentation
characterization were conducted to study the Ti-6Al-4V parts processed by
electron beam additive manufacturing. The effect of build height on the
microstructural evolution and mechanical properties was investigated. Columnar
prior β grains are shown on the side surface and equiaxed grains are presented
on the scanning surface. The top layers present finer columnar structure, while
the bottom layers show bigger percentage of α′ martensites owing to the high
cooling rate. Nanoindentation tests identify the highest elastic modulus of 127.9
GPa and hardness of 6.5 GPa.
Xibing Gong, Xiaoqing Wang and Kevin Chou
Mechanical Engineering Department
The University of Alabama
Tuscaloosa, AL 35487
xgong2@crimson.ua.edu
ASME Poster MSEC2014-4216
Fig. 1 Configuration of EBAM machine
Application: Aerospace, Military, Biomedical;
Complex/Unique Geometry/Structure;
Customized, Small Batch.
Advantages: Metal, Alloy, Intermetallic alloys; High Scan
Rate; Fine Microstructure; Lower Residual Stress.
Challenges: Accuracy, Surface Finish, Powder Variation,
Process Sensitivity, and Process Monitoring.
Fig. 2 Nanoindentation setup Fig. 3 Load vs. time
Fig. 11 Test samples
Fig. 5 Raw powders Fig. 6 Sintered powders
X-plane Z-plane
Top
Middle
Bottom
Fig. 7 OM of samples with different build heights
Top Middle Bottom
Fig. 8 SEM of samples with different build heights
Fig. 9 SEM of lamella α of parallel
bundles with very small amounts of β in
the α boundaries
Fig. 10 Microstructure of mixed α′, α and
β due to high cooling rate during
solidification
127.09
120.06 122.12118.71
114.2 117.57
100
105
110
115
120
125
130
135
140
Top Middle Bottom
ElasticModulus(GPa)
Z-Plane
X-Plane
4.97
5.84
3.47
3.29
4.17 3.14
6.47 6.09 6.225.6 5.75 5.86
2
3
4
5
6
7
8
Top Middle Bottom
Hardness(GPa)
Z-Plane
X-Plane
0.41
0.51 3.14
0.29
0.31 0.33
Fig. 4 Indent pattern
Fig. 12 Force-displacement
Fig. 13 Elastic modulus
Fig. 14 Hardness