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. 2022 Aug 1;15(15):5302. doi: 10.3390/ma15155302

Table 1.

Microstructures of metal foams fabricated by melt foaming and powder metallurgy technique.

Manufacturing Techniques Material Foaming Agent/Space Holders Microstructure Reference
Melt foaming Al matrix,
graphene 		NaCl, KCl and PMMA
  • -

    Closed pores due to incomplete dissolution of NaCl primarily due to hinderance offered by the high dense samples.

  • -

    Good interfacial bonding strength between the Al matrix and the NaCl interface.

  • -

    Lesser micro-porosities due to high dense material manufactured through the MI process.

 [49]
Al-Si13-MgX (X = 2.5–15 wt %) alloy Mg
  • -

    Porous structure exhibited microporosity, broken/missing/cell walls and elliptical cells, as a result of merged pores.

 [50]
AlMg50, Ca TiH2
  • -

    Uniformly distributed Mg in the matrix.

  • -

    Due to the restriction effect of cell walls, the grain morphology of primary α-Al in cell walls of Al foams is irregular.

  • -

    Cell-wall grains are much smaller than those in the pore-free layer.

 [48]
A356 foams CaCO3
  • -

    The stabilization was achieved due to foaming gas (CO)/melt reaction during foaming producing CaO, Al2O3 and MgO.

  • -

    The porosity increased with holding time.

  • -

    The cell size increased with increase in CaCO3 content.

 [51]
Powder metallurgy
Using foaming agent AlSi10
alloy		 TiH2
  • -

    Alloy and the reinforcements are bonded metallurgically strong.

  • -

    As the temperature rises to 150 C, the matrix softens and undergoes plastic deformation of the cell walls.

 [52]
Mg, Al, Cu, and Zn, yttrium TiH2
  • -

    Large number of closely packed gas-filled pores.

  • -

    Uniformly distributed and few elliptical pores.

 [53]
AlMg4Si8 alloy and multi-walled carbon nanotubes (MWCNT) TiH2
  • -

    Good dispersion of MWCNT in aluminium alloy foam.

 [54]
Space holder technique Ti-based Cu alloy Acrawax
  • -

    Cells obtained in the foams were nearly circular and mostly interconnected.

[55]
Steel
(iron, graphite phosphorous)		 Urea granules
  • -

    Uniformly distributed spherical cells between the cell walls.

  • -

    Sintering temperature and applied pressure have the weakest and strongest effect on the porosity.

 [56]
Aluminium, Graphene NaCl, KCl, and
PMMA
  • -

    Primarily composed of closed macro-pore structures.

  • -

    Pore morphology same as that of space holders.

  • -

    Process produced the desired closed pore structure.

  • -

    With increase in volume fraction of the space holder, the cell walls became thinner, and density decreased.

 [49]
316L austenitic stainless steel Urea particles
  • -

    Cell size was comparable to that of space-holder particles.

  • -

    Cells are mostly interconnected, open, and spherical in shape.

  • -

    Cell walls are larger in size.

  • -

    Thinner cell walls with microporosities as a result of higher evaporation rate of the space holder.

  • -

    Strong cell wall with low microporosity.

[57]
Al matrix and MWCNT Urea
particles
  • -

    Uniformly distributed pores formed in the foam structure with shapes similar to spherical urea granules.

  • -

    Large number of pores formed across the cross-section of the foams with increase in urea content.

 [58]