Metallic foams find increasingly more interest as structural materials. This is to a large extent due to high stiffness in conjunction with very low specific weight and high energy-absorption capability. Amorphous metallic foams are particularly interesting because the use of BMGs in a cellular structure eliminates their limited plasticity, their exceptional high strength over modulus ratio allows for elastic buckling, and their access to a processing viscosity region where gravitational effects can be neglected. Since foam is an unstable structure, the process of foaming of pure metals is a challenging task. The high viscosity of BMG formers provides a significant processing advantage for the synthesize of porous BMG. Our initial focus was on foaming BMGs in its (stable) liquid state we recognized significant limitations of any foaming process of BMGs that takes place in its stable liquid. This includes the size limitation to the BMGs critical casting thickness, and very limited control over bubble volume fraction and bubble size. Therefore, we developed an alternative synthesize process based on TPF which lifts the size limitation and allows to produce large (up to 10 times larger than critical casting thickness) foams where a large control over bubble size and volume fraction can be achieved. Currently we are exploring synthesize methods that result in small pores, < 10 μm open cells. Also we are developing methods that are ubiquitously applicable to a wide range of BMGs. Combining blow molding and foaming is also explored to net-shape foams where the porosity is independent of the articles geometry.
Thermoplastic blow molding and forming can be combined to net-shape amorphous metallic foams into complex geometries.
Amorphous metallic foam made by liquid expansion. Porosities of up to 80% can be achieved with this method.
Amorphous metals foams fabricated through thermoplastic forming based expansion with a density of 0.63 g/cm3 and corresponding porosity of 93%. The porosity is distributed uniformely in pores of approximately 1 mm in diameter.