Titanium offers a high specific strength, low density, and excellent corrosion resistance. It finds application in many fields like automotive, aerospace, drilling, and biomedical industries. To improve the adherence of bone cells on implants a rough surface can be of advantage. Such a surface is featured by a foamed stru cture. For achieving a foamed Ti structure, laser induced foami ng was used. In this case, Ti powder is pre mixed with foaming agents. The foaming agents are degraded by laser induced energy and produce gaseous products like carbon dioxide, while the Ti powder is molten by the laser. Due to the fast cooling rate carb on dioxide forms gaseous bubbles in the solidifying material. Mandatory for the foaming agents is that they are biocompatible. Previous studies using the foaming agents CaCO 3 , MgCO 3 , MgTiO 3 , and MgTiO 3 mixed to Ti powder resulted in a porosity of up to 0.3. By varying the content of the foaming agent por osity and pore diameter of the samples were adjusted. It is expected that an increased porosity could be achieved by mixing the foaming agents among each other. The influence of the specific foaming agents and their mixtures on the porosity is pres ented in this work. By mixing the foaming agents together and adding them to the powder, the porosity of the samples was increased compared to only adding one foaming agent to the powder

Gesing, Thorsten M.

Haferkamp, Heinz

Kaierle, Stefan

Noelke, Christian

Pape, Florian

AbstractTitanium offers a high specific strength, low density, and excellent corrosion resistance. It finds application in many fields like automotive, aerospace, drilling, and biomedical industries. To improve the adherence of bone cells on implants a rough surface can be of advantage. Such a surface is featured by a foamed structure. For achieving a foamed Ti structure, laser induced foaming was used. In this case, Ti powder is pre mixed with foaming agents. The foaming agents are degraded by laser induced energy and produce gaseous products like carbon dioxide, while the Ti powder is molten by the laser. Due to the fast cooling rate carbon dioxide forms gaseous bubbles in the solidifying material. Mandatory for the foaming agents is that they are biocompatible. Previous studies using the foaming agents CaCO3, MgCO3, MgTiO3, and MgTiO3 mixed to Ti powder resulted in a porosity of up to 0.3. By varying the content of the foaming agent porosity and pore diameter of the samples were adjusted.It is expected that an increased porosity could be achieved by mixing the foaming agents among each other. The influence of the specific foaming agents and their mixtures on the porosity is presented in this work. By mixing the foaming agents together and adding them to the powder, the porosity of the samples was increased compared to only adding one foaming agent to the powder

Elsevier - Publisher Connector 

 Procedia Materials Science  4 ( 2014 )  97 – 102 
Available online at www.sciencedirect.com
ScienceDirect
2211-8128 © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
Peer-review under responsibility of Scientifi c Committee of North Carolina State University
doi: 10.1016/j.mspro.2014.07.606 
8th International Conference on Porous Metals and Metallic Foams, Metfoam 2013 
Influence of foaming agents on laser based manufacturing of closed-
cell Ti foam  
Florian Papea, *, Christian Noelkea, Stefan Kaierlea, Heinz Haferkampa, Thorsten M. 
Gesingb 
aLaser Zentrum Hannover e. V. (LZH) Hollerithallee 8, 30419 Hannover, Germany 
b Institut fuer Mineralogie Leibniz Universitaet Hannover 30167 Hannover, Germany 
Abstract 
   Titanium offers a high specific strength, low density, and excellent corrosion resistance. It finds application in many fields like 
automotive, aerospace, drilling, and biomedical industries. To improve the adherence of bone cells on implants a rough surface 
can be of advantage. Such a surface is featured by a foamed structure. For achieving a foamed Ti structure, laser induced foaming 
was used. In this case, Ti powder is pre mixed with foaming agents. The foaming agents are degraded by laser induced energy 
and produce gaseous products like carbon dioxide, while the Ti powder is molten by the laser. Due to the fast cooling rate carbon 
dioxide forms gaseous bubbles in the solidifying material. Mandatory for the foaming agents is that they are biocompatible. 
Previous studies using the foaming agents CaCO3, MgCO3, MgTiO3, and MgTiO3 mixed to Ti powder resulted in a porosity of 
up to 0.3. By varying the content of the foaming agent porosity and pore diameter of the samples were adjusted.  
It is expected that an increased porosity could be achieved by mixing the foaming agents among each other. The influence of the 
specific foaming agents and their mixtures on the porosity is presented in this work. By mixing the foaming agents together and 
adding them to the powder, the porosity of the samples was increased compared to only adding one foaming agent to the powder. 
 
© 2014 The Authors. Published by Elsevier Ltd. 
Peer-review under responsibility of Scientific Committee of North Carolina State University. 
Keywords:Ti Foam; Foaming agents; Laser based foaming; Ti implants; Nanoindentation 
 
 
* Corresponding author. Tel.: +49-511-761-9147; fax: +49-511-2788-100. 
E-mail address:Florian.Pape@gmx.de 
© 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
Peer-review under responsibility of Scientifi c Committee of North Carolina State University
98   Florian Pape et al. /  Procedia Materials Science  4 ( 2014 )  97 – 102 
1. Introduction 
   Processing of metallic foams is investigated at the Laser Zentrum Hannover e. V. (LZH) since 1999 
(Haferkamp et al. (1999)). Very interesting as metallic foam for implants is a Ti foam. Ti offers particularly a great 
biocompatibility (Higuchi et al. (2005), Maekawa et al. (2005), Sakamoto et al. (2005), Bannon and Mild (1983)). A 
laser based process offers itself for application to make a Ti foam. By conventional methods Titanium and its alloys 
are difficult to machine and the processing causes high tool wear (Weinert and Petzoldt (2004), Hohenhoff et al. 
(2005)). Using a laser based process titanium foam structures with dense, closed outer skin can be realized. The 
porous foamed core is generated by adding foaming agents to the titanium powder. A structure comparable to 
cancellous bone should be realized. To allow implants for different bone types, a wide range of foaming agents were 
chosen and even mixed with each other. To generate such foams near net shape would allow for application in 
medicine. An advantage is a rough but closed outer skin of the foamed structures allowing for good cell adherence 
on the implant (Diefenbeck et al. (2011)). The laser based foaming of titanium is presented in this contribution. 
2. Experimental 
   To machine the Ti foam a diode laser system at a laser power of 350 watts was chosen. The laser diameter at its 
focus was 860 nm, the wave length was 940 – 980 nm. The process was performed in a reaction chamber under Ar 
as inert process atmosphere. The setup of laser head and shielding box is depicted in Fig. 1. A special powder 
reservoir with five grooves for the Ti powder was placed in the reaction chamber (Fig. 2). In each groove 2.5 g 
powder of the same mixture was deposited to achieve five samples for analysis in one processing step. 
As powder Ti with a particle size between 75 µm and 100 µm was mixed with the respective foaming agents. For 
the foaming agents the decomposition temperatures were chosen to be lower than the melting temperature of Ti with 
1,933 K. Each of the foaming agents dissociates at a specific temperature. The specific decomposition temperatures 
are for: 
• calcium carbonate (CaCO3) 1,181 K (Wiberg (1971)) 
• magnesium carbonate (MgCO3)  813 K (Wiberg (1971)) 
• magnesiumtitanate (MgTiO3)  1,813 K (Wechsler and Navrostsky (1984)) 
The foaming process leaded to a lot of smog that was removed by a suction placed close to the reaction chamber. 
After processing, the welding beads were cleaned from residual particles in a ultrasonic bath. To measure the 
porosity a pycnometer was used. Next the welding beads were cut and polished for optical evaluation. The Ti matrix 
was inspected by energy-dispersive X-ray spectroscopy (EDX). To achieve the hardness and Young’s Modulus of 
the Ti Matrix, nanoindentation techniques were used. 
 
 
 
 
Fig. 1. Setup for Ti foaming 
 
 
99 Florian Pape et al. /  Procedia Materials Science  4 ( 2014 )  97 – 102 
 
Fig. 2. Powder reservoir in reaction chamber 
 
 
3. Results and discussion 
   The foaming process could be established with the presented setup. By the laser induced energy Ti was molten 
and the foaming agent dissociated. In the process, the molten Ti and gaseous bubbles agglomerated on solidified 
material and a porous sample could be achieved. Exemplary welding beads foamed with 0.7% CaCO3 and 1.9% 
CaCO3 are depicted in Fig. 3. The concentration of the foaming agent has a significant influence on the porosity. If a 
high amount of foaming agent is added, the pores are too big, the foam collapses. 
Thus, for the specific foaming agents a working area was defined. At a concentration of foaming agent between 
1.0% and 1.3% best results were achieved. For this work the values with a concentration of 1 % foaming agent were 
considered. Applying CaCO3 as foaming agent the biggest pores were realized. With an increased content of CaCO3 
as foaming agent the foam collapsed. The highest porosity could be achieved by inserting MgCO3 as foaming agent. 
With a high content of foaming agent the foam collapsed, too. In case of MgTiO3 as foaming agent a porosity of 
0.26 could be established (Fig. 4). For this foaming agent the foam was stable even for higher contents of foaming 
agent. In case of MgTiO3 as foaming agent additional carbon was added to improve the reaction to gaseous carbon. 
A slightly increase of porosity could be achieved for this foaming agent by addition of carbon. The process was 
reproducible for all foaming agents. The specific foaming characteristics of the foaming agents can be corresponded 
to their specific decomposition temperatures and the specific kinetics of their foaming processes. The achieved 
porosities at 1% of foaming agent concentration are depicted in Fig. 5. Fig. 6 shows cross sections of samples 
foamed with 0.4% and 1% MgCO3 as foaming agent. The influence of the increased content of foaming agent to the 
pore size is obvious. 
 
 
 
Fig. 3. Foamed welding beads: a) foamed with 0.7% CaCO3, b) foamed with 1.9 % CaCO3 
 
 
a) 0.7% CaCO3 
 
b) 1.9% CaCO3 
100   Florian Pape et al. /  Procedia Materials Science  4 ( 2014 )  97 – 102 
 
Fig. 4. Porosities for Ti foam foamed with MgTiO3 and MgTiO3+ C as foaming agent 
 
 
Fig. 5. Porosities for Ti foam foamed with 1 % of foaming agent 
 
a) b) 
  
Fig. 6. Cross sections for Ti foam samples with: a) 0,4%, b) 1% MgCO3 as foaming agent 
 
 
The highest porosities could be achieved by mixtures of foaming agents. The foaming agents were mixed to the 
Ti powder that at total a foaming agent concentration of 1% could be achieved. Fig. 7 depicts the porosities 
(measured with pycnometer) of samples foamed with mixtures of foaming agents. The mixture of MgCO3 and 
MgTiO3 as foaming agents (each with a concentration of 0.5% in the powder) had the lowest porosity with a value 
of 0.25. In this case a mixture shows no improvement of the porosity. By mixing CaCO3 and MgTiO3 as foaming 
agents the porosity was increased to a value of 0.33. A mixture of CaCO3 and MgCO3 as foaming agents had a 
porosity of 0.34. In case of mixing CaCO3, MgCO3, and MgTiO3 as foaming agents (each with a concentration of 
0.33% of the powder) a porosity of 0.36 was realized. The addition of carbon brought no advantage in this case. 
Exemplary a µ-CT (micro-X-ray computed tomography) scan of a sample foamed with a mixture of MgCO3, 
CaCO3, and MgTiO3 is depicted in Fig. 8. For this sample the measured porosity on the cut-through was 54%. 
Energy-dispersive (EDX) X-ray spectroscopy was conducted on foamed samples to analyze for contaminations of 
the Ti matrix. For all samples the matrix shows no content of foaming agent. At the pore wall the content of 
contaminations was below 0.02% for all samples. This value is within the EDX threshold. 
101 Florian Pape et al. /  Procedia Materials Science  4 ( 2014 )  97 – 102 
To evaluate exactly the mechanical properties of the thin walls of Ti foam, it is mandatory to use a system 
allowing for a displacement in the range a few ten nm to a few microns and with a precision in the nm range. A 
system lending itself for application is a nanoindentation system. This is commonly used to measure hardness and 
Young’s modulus of thin diamond-like carbon (DLC) coatings and thin layers (Pape and Gatzen (2008), Pape 
(2011)). The mechanical properties of the Ti matrix allow judging the influence of the foaming process and foaming 
agents on the Ti matrix. A load between 1 µN and 10 mN and a displacement of up to 5 µm could be realized by the 
test system. On a sample 80 indents were performed in the Matrix on a foam wall. A load of 5 mN was chosen, for 
measurement a Berkovich tip with 80 nm tip radius was applied. The Young’s Modulus and hardness were 
evaluated by the method of Oliver and Pharr (Oliver and Pharr (1992)). The hardness was 4,6 GPa with a derivation 
of 1,2 GPa, the Young’s Modulus was 132,9 GPa with a derivation of 6,4 GPa. The measured data are slightly 
higher than values reported in literature (Mante et al. (1999), Tam et al. (2009)). 
 
 
 
Fig. 7. Porosities for Ti foam foamed with mixtures of foaming agents (measured with pycnometer) 
 
 
Fig. 8. Micro-CT image of foamed titanium specimen, foamed with mixture of CaCO3, MgCO3, and MgTiO3 
 
 
4. Conclusions 
   For all foaming agents a stable foaming process could be established. In the process and for the samples each 
foaming agent shows its own characteristics. This effect can be referred to the various decomposition temperatures 
and the specific reaction kinetics. Thus a mixture of the foaming agents allowed for obtaining an increased porosity, 
as the gaseous bubbles react at different temperature stages. For further investigations, foaming agents with a higher 
decomposition temperature like lithium carbonate or strontium carbonate should be investigated next. Finally it’s 
planned to realize higher amounts of foam by stacking layer by layer of the welding beads. So far, the highest 
porosity in laser induced foam samples could be obtained for a sample foamed with a mixture of foaming agents. By 
mixing the foaming agents MgCO3, CaCO3, and MgTiO3 (altogether 1% concentration) a porosity of 0.36 
(measured by a pycnometer) was reached. The samples itself show a closed metal foam with a completely molten 
and dense matrix. Only a small amount of foaming agents could be detected using EDX analysis at the pore walls. It 
could be shown by nanoindentational measurements, that the Ti matrix has the mechanical properties as pure Ti. 
102   Florian Pape et al. /  Procedia Materials Science  4 ( 2014 )  97 – 102 
Acknowledgment 
 
   The authors gratefully acknowledge the funding of the reported work by the German Science Foundation 
(Deutsche Forschungsgemeinschaft, DFG) within the project “Laserbasierte Erzeugung von Titan-Schaumstrukturen 
aus der Flüssigphase durch Gasfreisetzung oder Induzierung eines gasbildenden Prozesses aus einem Treibmittel” 
(HA 1213/72-1). Th.M. Gesing especially likes to thank the DFG for support in the Heisenberg program 
(GE1981/3-1). 
 
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Influence of Foaming Agents on Laser Based Manufacturing of Closed-cell Ti Foam 

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Influence of foaming agents on laser based manufacturing of closed-cell Ti foam

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Influence of foaming agents on laser based manufacturing of closed-cell Ti foam

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