Steel and Titanium Hollow Sphere Foams

Abstract

Metal hollow sphere foams are fabricated by bonding millimeter sized metal alloy hollow spheres at points of contact. The spheres are formed as powder shells from slurries. For stainless steel spheres, the starting powder is a mixture of iron and chromium oxide. Thermal treatment in hydrogen reduces the oxides to Fe/Cr alloys with less than 2% porosity in sphere walls. The nominal composition is close to that of 405 stainless. Carburization in CO/CO2 atmosphere followed by heat treatment produces foams of either 410 or 420 type stainless steels depending on carbon content. Compressive stress-strain behavior was measured on point contact bonded stainless foams both before and after carburization. Hardness measurements on steel sphere walls were used to estimate the yield strength. Relative strengths of the foams were positioned between open and closed cell models. This was encouraging because bonding in the foams was less than optimum and the hollow sphere walls contained defects. As processing improves, strengths should increase. To produce titanium alloy spheres, the starting powder is titanium alloy hydride. Thermal treatment in an inert atmosphere decomposes the hydride and sinters the titanium powder in the sphere walls to greater than 96% relative density. Both titanium and Ti-6V-4V spheres and foams have been produced. Oxygen contents are a concern for titanium compositions and processing is being altered to reduce oxygen levels to increase ductility

Fabrication, microstructure and compressive behavior of ZC63 Mg–microballoon foam composites

“…The foam composites can be made by incorporating carbon, glass, and alumina microballoons into metallic matrices [7][8][9][10]. Since the microballoons have lower density than the matrix, the density of the foam composite is significantly reduced by incorporating microballoons in the matrix.…”

Metallic Foams

“…Hollow spheres made of titanium or steel can be used to form highly porous structures by sintering [67,68]. Small expandable polystyrene foam spheres are spray coated with a metal powder suspension and dried.…”

Procesos de fabricación de metales celulares. Parte II: Vía sólida, deposición de metales, otros procesos

“…Posteriormente, las esferas son tratadas térmicamente para eliminar la fase líquida restante y otros componentes. Una producción típica de esferas puede estar entre 3.000 y 15.000 esferas/min, las cuales poseen diámetros entre 1 y 6 mm y espesores entre 40 y 200 µm [120] . Además, mediante el empleo de mezclas de Fe 2 O 3 /Cr 2 O 3 en la barbotina, se pueden crear esferas de acero inoxidable mediante la reducción de las mismas en atmósfera de hidrógeno/argón a 1.400 °C [121] .…”