Solid State Porous Metal Production: A Review of the Capabilities, Characteristics, and Challenges

Abstract

Porous metals have been under development for nearly a century, but commercial adoption remains limited. This development has followed two primary routes: liquid state or solid state processing. Liquid state foaming introduces porosity to a liquid or semi‐solid metal, and solid state foaming introduces porosity to a metal, which is fully solid. Either method may create pores by internal gas pressure or introducing metal around a template directly control porosity. Process optimization and commercial output has been primarily related to liquid state methods, as solid state processing is often more complex, diverse, and with lower throughput. Solid state methods, however, are often more versatile and offer greater control of pore characteristics. Ongoing advancements in solid state foaming have allowed for a wide array of metals and alloys to be made porous and the three‐dimensional structure to be precisely tailored. In general, solid state processing remains limited to niche applications, often with modest dimensions (cm scale). “Traditional” solid state processes are being further refined and extended, and continuing developments to reduce cost, increase output, and control pore characteristics are likely to produce important advancements in coming years. The extensive variability of pore quantity and morphology makes solid state processes suitable, and often preferable, for an assortment of functional and structural applications, with electrodes and biomedical devices being among the most popular in current research. Various techniques for introducing porosity, the way these methods are applied, important considerations, typical outcomes, and current applications are reviewed.

Multifunctional porous catalyst produced by mechanical alloying

“…The primary application of this powder is accelerated CNF deposition, but the same processing strategy can be applied for diverse functional purposes. For instance, nanostructured catalytic powder may be consolidated to create large-scale metallic foams by traditional solid state foaming methods, as recently reviewed [36], and used for electrodes, filtration, and other functional designs. The CNFs produced also have diverse applications, especially as free-standing nanofibrous aerogel materials [37].…”

Biomedical Porous Shape Memory Alloys for Hard-Tissue Replacement Materials

“…Generally speaking, porous metals with closed pores exhibit mechanical properties that are better than that with open pores at the same porosity [ 42 ]. However, the open pores are an often desirable structure for porous scaffolds in bone replacement materials to allow for cell attachment or body fluid exchange [ 43 , 44 ]. Thus, to control porous structure is one basic issue for biomedical porous NiTi SMAs [ 42 , 45 ].…”

The Neck to Particle Ratio Effect on the Mechanical and Morphological Sintering Features of Porous Stainless Steel (SS) Hollow Fibers

“…It is well known that the mechanical strength of sintered materials are directly associated with the ability of particles to contact each other and to form necks [15], which facilitates mass transfer and densification during sintering [16]. If graded and/or porous metallic materials are desired for specific applications, then the sintering conditions must be controlled otherwise full densification takes place [17]. Although sintering of metal particles has been extensively investigated [18], the morphological features of SS hollow fibres differ from those studies where SS particles are in close contact of each other during sintering.…”