Structural and Material Design of Open‐Cell Powder Metallurgical Foams

Abstract

Open cell foams made on the basis of reticulated polyurethane foams are well known and widely used since decades. Polyurethane foams have been commercially produced since the 1950 s. [1] They are a practically ideal porous organic structure with porosities between 97 and 98%. First attempts to transfer these structures into ceramic foams by a powder slurry replication technique have been described by Schwartzwalder in 1961, [2] and nowadays such foams are produced in the order of 160 million parts per year for the use as filter in the cast shop. The replication technique has been transferred into the manufacturing of metal foams for the first time in 1966 in order to use them as porous battery electrodes. [3] In the 1970 s, notable work has been done by Russian research groups, where metal foams made by replication method were mainly used in catalysis or filtration applications. [4] Over the past ten years the method has been reinvented by various groups. Mainly open cell foams on the basis of highly alloyed steels were produced, [5][6][7][8] but also foams on the basis of copper [9] or titanium alloys for the use as permanent biomedical implant [10] or low alloyed steel for degradable implants [11] were investigated. In the present work, open cell metal foams have been developed on the basis of various steels like SUS 316L, SUS 314, 4110, SUS 430L, FeCrAl, mild steels and non-ferrous metals like molybdenum, tantalum and the titanium alloy Ti6Al4V. The present paper shows the main properties and applications of replicated PU based metal foams. ExperimentalThe replication method essentially involves three production steps: First, a reticulated polyurethane sponge is coated by slurry impregnation. Reticulated polyurethane foam samples with cell sizes of 10, 30, 45, 60, and 80 pores per inch (Foampartner Reisgies, Germany) were coated using double rubber rollers. Water-based slurries with PVA-binder or carbon acid binder and solids content between 87 and 90% were used. In the next step, the template is thermally removed and finally the debinded metal structure is sintered.Thus, the open network of the polymer foam is transformed into a metal structure. The processing in principle is rather simple, but however, in order to obtain defect-free structures with optimum properties every single processing step needs for proper development. Firstly, in order to obtain complete impregnation of the PU foams fine metal powders High porosity permeable materials have been manufactured on the basis of the highly uniform structure of foamed polyurethane since the 1950 s. This paper shows the development of open cell foams based on all kinds of steels, titanium alloys, and also open-cell molybdenum foams made by a powder metallurgical replication technique. Such materials show a wide range of physical and mechanical properties, which may be adapted to various requirements. The automotive industry, for example, needs high-temperature resistant materials with high permeability and good strength for catalytic conversion. For orthopaed...

Fabrication of Porous Stainless Steel 316L for Biomedical Applications

“…This method capable of producing metal foams with a porous structure that most resembles cancellous bone [6]. However, every single processing step needs for proper study and exploration in order to obtain defect-free structures with optimum properties [7]. Figure 1 shows that the microstructure of the natural bone is almost similar to the microstructure of polyurethane (PU) foam used as a sacrificial template for this work.…”

Production of 316L Stainless Steel (SS316L) Foam via Slurry Method

“…This type of alloy has become known in the production of biomedical applications because of its good mechanical properties and excellent corrosion resistance (Ding, Wang, Li, & Zheng, 2010;Hermawan et al, 2011;Roguska et al, 2011). Open cell foams based on polyurethane (PU) foam have been made using the slurry method (Quadbeck et al, 2011). Because of their good physical and mechanical properties together with their biocompatibility characteristics, polyurethanes (PUs) are used widely in biomedical applications such as heart valves, aortic grafts, and dialysis membranes, pacing leads insulation, indwelling catheters, intra-aortic balloons and mammary implants (Wadley, 2002).…”

“…The binder and blowing agent affect the slurry, so that it becomes viscous and expands. Researchers have succeeded in producing metallic foam via the slurry method to produce many types of steels, titanium alloys, and also open-cell molybdenum for various applications (Quadbeck et al, 2011). In addition, others have studied aluminizing nickel foam by a slurry coating process and have succeeded in coating nickel with aluminium (Omar et al, 2009).…”

The effect of slurry composition on the microstructure and mechanical properties of open-cell Inconel foams manufactured by the slurry coating technique

“…Note that the fine metal powders are suggested for the slurry because the use of metal powder particles exceeding 25 µm for the slurry often results in structural defects and voids deep within larger foam pieces [5]. Open-cell foams of stainless steel [5], carbonyl iron [5], Fe-Cr-Al [5,10], aluminium [9], titanium [2], Ti-6Al-4V [5,8,11] and molybdenum [5] have been successfully fabricated using the slurry coating method. However, the production of foams for applications involving exposure to high temperature environments requires that superalloys be used as foam materials.…”

“…Solid state processing methods involve the use of metal powders and are especially preferred when the alloy of the foam (e.g., Ni) to be produced has a high melting temperature [1]. Among the solid state processing methods, the slurry coating technique can produce open-cell metal foams with the lowest relative densities [2][3][4][5][6]. In this method, an open-cell polymeric sacrificial template is first coated with the metal slurry.…”