| Liquid metallurgy route |
Melt gas injection |
Large volume production, low-density metallic foam |
Foam stabilization, imperfections, and inconsistencies, controlling
the foam quality, and optimizing processing parameters |
(6, 62, 63) |
| |
Blowing agent |
formation of foam in several types of alloys, including lightweight
alloys and low-density metallic foam |
Inflated cost of
hydride blowing agent, controlling porosity
and cell size is challenging, not suitable for creating intricate
structures or shapes, optimizing processing parameters. |
(4, 33) |
| |
Dissolved gases (solid gas eutectic solidification-GASAR) |
Good for a variety of steels, cobalt, chromium, molybdenum,
and even ceramics |
GASAR metallic foams may exhibit unsatisfactory
homogeneity
sometimes; pores size depends upon cooling rate; the process requires
complicated equipment and turns out to be expensive; limited to metal
which forms eutectic systems with hydrogen gas |
(9, 33, 45) |
| |
Space holder (infiltration method) |
Cost-effective with an affordable space holder, particularly
effective for close foam-to-dense metal bonding in parts like sandwich
beams, enabling precise control of pore size, and distribution via
space holder grain size |
A challenging process demanding
extreme caution to fill a mold
with molten metal |
(9, 12, 45) |
| |
Foam replication (investment casting) |
Gives flexibility
in terms of the choice of metal; the process
is simpler to implement, resulting in highly porous and high-quality
foam. |
The drawback of this method is the complete filing
of mold,
directional solidification, and removal of mold without damaging fine
structure due to the high percentage of porosities. |
(33, 45, 62) |
| Powder metallurgy route |
Blowing
agent |
The manufacturing process excels in producing
high-quality
foams, fabricating intricate parts, accommodating a variety of metals
and alloys, and easily preparing sandwich panels. |
Expensive
method due to its two-step compacting process, controlling
foaming duration for high-quality foam |
(9, 33, 45, 62, 110) |
| |
Space holder |
Controlled pore morphology,
higher compressive strength, low
cost, and easy to handle |
Removal of complete space holder
material, nonuniform properties,
and Limited porosity. |
(6, 9, 34, 154) |
| |
Gas entrapment technique |
Mainly used to create porous lightweight titanium structures |
Mostly limited to titanium and its alloy, The process requires
complex equipment and turns out to be expensive. |
(111, 122) |
| |
Foaming of slurries |
The ability to produce ultralight
materials with high porosity
is a potential advantage. |
Insufficient strength issues
and potential foamed material
cracks may arise. |
(45, 64, 84) |
| |
Loose powder sintering |
Fine porosity can be created
intentionally during the manufacturing
process. |
Commonly used for bronze; products have comparatively
low strengths. |
(45) |
| |
Additive Manufacturing |
This technique offers stately design flexibility, allowing
for small and precise structures with complex internal shapes, reduced
material waste, cost-effectiveness, and rare shape-making ability. |
Inflated cost of equipment and materials; skilled operators
required, limited range of material for foam fabrication |
(9, 84, 139) |
| Deposition route |
Metal Vapor |
Low density, high stiffness with good energy absorption properties,
customizable design flexibility |
Limited to small-scale
production due to high processing costs |
(9, 33, 62) |
| electrochemical deposition route |
Metal ion
solution |
Used to produce nanoporous structure; foam
possesses good electrical
impedance and a large surface area. |
limited to small-scale
manufacturing because of the expensive
processes involved |
(9, 33, 62, 152) |
