Processing, stabilization and applications of metallic foams. Art of science

Metallic foams have been of considerable interest both from the industrial applicability and scientific viewpoint. In the last three decades, since the inception of the metal foam, several processes have been developed to introduce large size pores, almost uniformly distributed, in the metallic materials. These processes include liquid metal route, powdered metal technique and some other methodologies in which pores are incorporated by direct sintering of foamed elements. Metallic foams have seen tremendous innovations for the last few years and efforts are being made to achieve foams with a low cost and with reliable properties. The stability of cell structure during the foaming process has also been a concern for researchers. Therefore, methods have been explored to increase the stability by introduction of ceramic particles in the material to be foamed, addition of alloying elements, secondary processing of precursor materials, and by optimizing the process parameters. To this end, experiments have also been made in microgravity conditions to study the mechanism of foam formation which can give a better understanding for controlling the processing conditions. Despite the current development, there are several limitations for a wide applicability of metallic foams in various industrial sectors, such as high cost of production, variability in measured properties, and unavailability of reliable testing methods. Taking these facts into consideration, the present paper is aimed at reviewing various foam processing techniques, the measures required to be taken for making stable foams and the industrial applications of the metallic foams in the current state of development.