This article describes manufacturing procedures that produce aluminum foams and have since become industrially important and successful. It discusses the foaming of melts by blowing agents and foaming of melts by gas injection. The article focuses on aluminum foams based on the Foaminal technology, because those foams dominate the technical applications of aluminum foams. It also discusses the mechanical properties of metal foams, such as general compression behavior, elastic behavior, strain-rate sensitivity, tensile behavior, ductility, fatigue, and mechanical damping. The article concludes with information on the applications of highly porous metal structures.

Cellular or foam structures can be described by means of two broader cases: foams in which the pores are all connected to each other and with the environment (open-pore foams) and foams in which every single pore is completely enclosed by the matrix (closed-pore foams). This article describes the four process groups for the production of open- and closed-pore metal foams. It discusses the principles of the foaminal process with the description of various foaming agents, solidified metal foam, and geometries and derived structures of metal foams. The use of syntactic metal foam in various fields is included. The article reviews the mechanical properties of closed-pore metal foams, details the machining and joining procedures of the metal foams, and presents the applications of the metal foam.

Physically, tantalum is a dark, blue-gray, lusterless metal that exists in two crystalline forms: an alpha-phase with a body-centered cubic structure, and a brittle beta-phase with a tetragonal orientation. This article tabulates the physical and material properties of tantalum. It discusses the use of tantalum in medical electronics and the advantage of tantalum over stainless steel. The article describes the manufacturing and medical applications of tantalum foam.

Porous coatings are used in the field of joint replacement, particularly in cementless total hip/knee arthroplasty. This article reviews the offerings and biomaterial properties in orthopedic surgery for the contemporary class of highly porous metals. It describes the traditional porous metals/coatings having an open-cell structure, high porosity, and a microstructure resembling that of the cancellous bone. The traditional porous metal/coating includes fiber-metal mesh, cobalt-chromium (CoCr) beads, cancellous-structured titanium, and plasma spray. The article discusses other porous metals/coatings that have been developed due to the limitations of traditional porous metals for numerous open-cell-structured metals, such as titanium-base foams and trabecular metals.

Metal matrix composites (MMCs) can be synthesized by vapor phase, liquid phase, or solid phase processes. This article emphasizes the liquid phase processing where solid reinforcements are incorporated in the molten metal or alloy melt that is allowed to solidify to form a composite. It illustrates the three broad categories of MMCs depending on the aspect ratio of the reinforcing phase. The categories include continuous fiber-reinforced composites, discontinuous or short fiber-reinforced composites, and particle-reinforced composites. The article discusses the two main classes of solidification processing of composites, namely, stir casting and melt infiltration. It describes the effects of reinforcement present in the liquid alloy on solidification. The article examines the automotive, space, and electronic packaging applications of MMCs. It concludes with information on the development of select cast MMCs.