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Influence of SLM Processing Parameters on Mechanical ...
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SLM WHA Microstructural Investigation 1. C. Kamath, B. El-dasher, G. F. Gallegos, W. E., King, A. Sisto, Density of Additively-Manufactured, 316L SS Parts Using Laser Powder-Bed Fusion at Powers Up to 400W, December 23, 2013 2. Image from: additively.com 3. German, et al. (2008) 4. Global Tungsten & Powders Corp. 2018. 5. Kiran, U. Ravi, et al. "Effect of tungsten content on microstructure and mechanical properties of swaged tungsten heavy alloys." Materials Science and Engineering: A 582 (2013): 389-396. 6. Hong, et al. (2002) Figure 3. WHA Powder 2 cubes, printed on steel build tray with 30 μm layer thickness. Tyler Christ Materials Science & Engineering, Lehigh University Influence of SLM Processing Parameters on Mechanical Properties of Tungsten-Heavy Alloy Figure 4. (a) Typical LPS WHA microstructure with the same chemical composition, but different scale than (b) image [6], (b) Image of etched SLM WHA , (c) SEM image collected for SLM WHA SLM WHA Investigation Conclusions • Novel microstructure composed of extremely fine and irregular grains, unlike typical WHA microstructures § Due to high cooling rates from high thermal conductivity of tungsten and small areas of heating allowing the heat to transfer to the steel tray faster causing extremely fine grains • In preliminary SEM testing multiple phases are present in the resulting microstructure without further testing the phases and composition are unknown • Microhardness is 1.5-2 times HIGHER than literature values Acknowledgements Global Tungsten & Powders Corp., Loewy Institute, Wojciech Misiolek, Brian Slocum, Trevor Verdonik, Richard Vinci, Bart Bancewicz, Tzung Shin Gao, Michael Pires • 337 samples were printed across 11 different build trays as shown in Fig. 3. • The samples were 5mm x 5mm x 5mm cubes built on mild steel build trays • Powder type, laser power, exposure time, point distance, hatch spacing, and layer height were varied in these prints • 28 samples were investigated for microstructure and microhardness • Samples selected varied different parameters and optical density Introduction Selective Laser Melting Technique SLM is a powder-based process. A layer of powder is spread on a platform, and the powder is melted by a high energy-density laser with respect to the computer-generated final product. Each layer is deposited onto the previous and melted in place. A schematic of the process is shown in Fig. 1. Lehigh performs SLM with a Renishaw AM 400 printer with a reduce build volume (RBV) insert. It is possible to vary over 130 processing parameters to influence part quality [1]. Figure 1. (Left) Powder delivered with piston and flattened with roller. Then a Laser scan passes through the powder layer, melting it in place to form solid material.[2] (Right) SLM abilities at Lehigh University with the Renishaw Reduced Build Volume (RBV) left and Renishaw AM 400 Printer right References Tungsten is a refractory material, with a high melting point of 3,422°C. Its high hardness also contributes to difficulties in manufacturing through traditional processes, such as liquid phase sintering (LPS). However, additive manufacturing (AM) techniques like selective laser melting (SLM) may serve as a solution. Collaboration project between Lehigh University and Global Tungsten and Powder (GTP) where GTP provided two different types of chemically identical Tungsten Heavy Alloy (WHA) powders at 93wt% W-5.6wt% Ni-1.4wt% Fe and Lehigh performed SLM and materials characterization. The two different type of powder are: • Powder 1= “Mixed Powder” • Powder 2= “Pre-Alloyed Powder” Recoater assembly Guide rails Build piston Dosing piston Drive mechanism Overflow Renishaw AM 400 Renishaw Reduced Build Volume (RBV) Liquid Phase Sintered WHA WHA is usually processed through LPS. The LPS process is shown in Fig. 2 left image. In this project the microstructure and microhardness will be characterized and compared from the SLM WHA to the LPS WHA. The typical LPS WHA microstructure is found in the right image in Fig. 2 with large circular tungsten regions with a nickel and iron matrix phase around the tungsten grains. The typical microhardness values for both the tungsten phase and the Nickel and Iron matrix phase of LPS WHA are shown in Table 1 below. Microhardness: Swaged WHA Load 100g W Matrix 90W-7Ni-2Fe-1Co (wt%) 530±3 HV 428±2 HV 93W-4.9Ni-1.4Fe-.7Co (wt%) 529±4 HV 423±1 HV 95W-3.5Ni-1Fe-.5Co (wt%) 529±2 HV 416±3 HV SLM WHA Microhardness Measurements Shown in Table 1 are the expected microhardness values of LPS WHA. The range of expected values are labeled by two red lines shown in figure 5. The green values are an average microhardness value of each of the 28 samples we tested. The values that we have measured are 1.5-2 times the expected values from the literature. We have attributed this to the extremely fine microstructure as a result of high cooling rate observed during microstructural analysis. Figure 5. Microhardness measurements of SLM WHA in green and red lines showing range of literature values [5]. Figure 2. (left) LPS process [3] (right) Typical LPS WHA microstructure [4] Future Work Tensile testing and continue production of samples to address crack initiation and propagation and all mechanical properties Table 1. LPS WHA microhardness for both tungsten grains and matrix phase regions [5] In Fig. 4 (a) and (b) light optical images of the LPS WHA (a) and SLM WHA experimental (b) are shown next to each other. They are the same composition, but two different magnification and processing. Even with the two different scales there is a very fine grain structure, and the matrix and tungsten phases are unable to be determined in the SLM WHA sample (b). The extremely fine microstructure is attributed to the process that is being performed. Since SLM is a powder manufacturing process extremely fine microstructure are found when printing samples. In the SLM WHA image Fig 4 (b) the large black regions are pores. In Fig. 4 (c) a scanning electron microscopy (SEM) image showing 2-3 phases present; however the composition of these phases is still unknown. (b) (c)
Transcript of Influence of SLM Processing Parameters on Mechanical ...
SLM WHA Microstructural Investigation
1. C. Kamath, B. El-dasher, G. F. Gallegos, W. E., King, A. Sisto, Density of Additively-Manufactured, 316L SS Parts Using Laser Powder-Bed Fusion at Powers Up to 400W, December 23, 2013
2. Image from: additively.com3. German, et al. (2008)4. Global Tungsten & Powders Corp. 2018. 5. Kiran, U. Ravi, et al. "Effect of tungsten content on microstructure and mechanical properties of swaged tungsten heavy alloys." Materials Science and Engineering: A 582 (2013):
389-396.6. Hong, et al. (2002)
Figure 3. WHA Powder 2 cubes, printed onsteel build tray with 30 μm layer thickness.
Tyler ChristMaterials Science & Engineering, Lehigh University
Influence of SLM Processing Parameters on Mechanical Properties of Tungsten-Heavy Alloy
Figure 4. (a) Typical LPS WHA microstructure with the same chemical composition, but different scale than (b) image [6], (b) Image of etched SLM WHA , (c) SEM image collected for SLM WHA
SLM WHA Investigation
Conclusions• Novel microstructure composed of extremely fine and irregular grains, unlike
typical WHA microstructures§ Due to high cooling rates from high thermal conductivity of tungsten and
small areas of heating allowing the heat to transfer to the steel tray faster causing extremely fine grains
• In preliminary SEM testing multiple phases are present in the resulting microstructure without further testing the phases and composition are unknown
• Microhardness is 1.5-2 times HIGHER than literature values
AcknowledgementsGlobal Tungsten & Powders Corp., Loewy Institute, WojciechMisiolek, Brian Slocum, Trevor Verdonik, Richard Vinci, BartBancewicz, Tzung Shin Gao, Michael Pires
• 337 samples were printed across 11 different build trays as shown in Fig. 3.• The samples were 5mm x 5mm x 5mm
cubes built on mild steel build trays• Powder type, laser power, exposure time,
point distance, hatch spacing, and layer height were varied in these prints
• 28 samples were investigated for microstructure and microhardness• Samples selected varied different
parameters and optical density
Introduction
Selective Laser Melting TechniqueSLM is a powder-based process. A layer of powder is spread on aplatform, and the powder is melted by a high energy-density laserwith respect to the computer-generated final product. Each layer isdeposited onto the previous and melted in place. A schematic of theprocess is shown in Fig. 1. Lehigh performs SLM with a RenishawAM 400 printer with a reduce build volume (RBV) insert. It is possibleto vary over 130 processing parameters to influence part quality [1].
Figure 1. (Left) Powder delivered with piston and flattened with roller. Then a Laser scan passes through the powder layer, melting it in place to form solid material.[2] (Right) SLM abilities at Lehigh University with the Renishaw Reduced Build
Volume (RBV) left and Renishaw AM 400 Printer right
References
Tungsten is a refractory material, with a high melting point of 3,422°C. Its high hardness also contributes to difficulties in manufacturing through traditional processes, such as liquid phase sintering (LPS). However, additive manufacturing (AM) techniques like selective laser melting (SLM) may serve as a solution.Collaboration project between Lehigh University and Global Tungsten and Powder (GTP) where GTP provided two different types of chemically identical Tungsten Heavy Alloy (WHA) powders at 93wt% W-5.6wt% Ni-1.4wt% Fe and Lehigh performed SLM and materials characterization. The two different type of powder are:
• Powder 1= “Mixed Powder”• Powder 2= “Pre-Alloyed Powder”
Recoater assembly
Guide rails
Build piston
Dosing piston
Drive mechanism
Overflow
Renishaw AM 400
Renishaw Reduced
Build Volume (RBV)
Liquid Phase Sintered WHA WHA is usually processed through LPS. The LPS process is shown in Fig. 2 left image. In this project the microstructure and microhardness will be characterized and compared from the SLM WHA to the LPS WHA. The typical LPS WHA microstructure is found in the right image in Fig. 2 with large circular tungsten regions with a nickel and iron matrix phase around the tungsten grains. The typical microhardness values for both the tungsten phase and the Nickel and Iron matrix phase of LPS WHA are shown in Table 1 below.
Microhardness: Swaged WHA Load 100g W Matrix
90W-7Ni-2Fe-1Co (wt%) 530±3 HV 428±2 HV
93W-4.9Ni-1.4Fe-.7Co (wt%) 529±4 HV 423±1 HV
95W-3.5Ni-1Fe-.5Co (wt%) 529±2 HV 416±3 HV
SLM WHA Microhardness MeasurementsShown in Table 1 are the expected microhardness values of LPS WHA. The range of expected values are labeled by two red lines shown in figure 5. The green values are an average microhardness value of each of the 28 samples we tested. The values that we have measured are 1.5-2 times the expected values from the literature. We have attributed this to the extremely fine microstructure as a result of high cooling rate observed during microstructural analysis. Figure 5. Microhardness measurements of SLM WHA in green
and red lines showing range of literature values [5].
Figure 2. (left) LPS process [3] (right) Typical LPS WHA microstructure [4]
Future WorkTensile testing and continue production of samples to address crack initiation and propagation and all mechanical properties
Table 1. LPS WHA microhardness for both tungsten grains and matrix phase regions [5]
In Fig. 4 (a) and (b) light optical images of the LPS WHA (a) and SLM WHA experimental (b) are shown next to each other. They are the same composition, but two different magnification and processing. Even with the two different scales there is a very fine grain structure, and the matrix and tungsten phases are unable to be determined in the SLM WHA sample (b). The extremely fine microstructure is attributed to the process that is being performed. Since SLM is a powder manufacturing process extremely fine microstructure are found when printing samples. In the SLM WHA image Fig 4 (b) the large black regions are pores. In Fig. 4 (c) a scanning electron microscopy (SEM) image showing 2-3 phases present; however the composition of these phases is still unknown.
(b) (c)
