Selected Microstructural and Mechanical Properties of Open-Cell Metal Foams

Abstract

Iron has been used as a basic material for everyday tools and weapons since prehistoric times. After the 19th century, which saw the emergence of new technologies for the production of iron-based alloys, steel has become ubiquitous, especially in construction. Now, with dynamic changes in technology, there is a need for new classes of materials that exhibit new characteristics. Looking for inspiration and solutions to difficult problems, engineers and scientists all over the world have often used nature, the best source of knowledge. For example, Ashby [1] wrote, “When modern man builds large load-bearing structures, he uses dense solids: steel, concrete, glass. When nature does the same, she generally uses cellular materials: wood, bone, coral”. Numerous experiments have been carried out to verify concepts concerning the fabrication and application of structural sponge-like materials. Some of the first successful attempts to produce foam materials for structural purposes led to the creation of porous polymer membranes [2] and porous polymer electrolytes [3]. Much of the research in this area has focused on the fabrication of advanced metal foams [4]. Several technologies have been invented to produce metal foams with closed or open porosity, with a crystalline or amorphous structure, and with pores ranging from a micrometre to several millimetres in size [5] and [6]. These efforts have resulted in many new applications, e.g. aluminium sound absorbers, copper heat exchangers, and nickel battery electrodes. However, Arwade et al. [7] complained, “Steel is one of the most widely used engineering materials, yet today no foam using steel as the base material is commercially available”. Further research is thus essential to develop efficient and cost-effective methods to produce Fe-based foam materials with desirable properties [8] and [9]. Sintering is one of the cheapest and most efficient methods to fabricate porous iron-based materials. It is not necessary to reach the melting point of iron to obtain a desired structure; porosity is achieved by using a space holder or a foaming agent. Bekoz and Oktay [10] fabricated sintered low-alloy steel foams using the space holder-water leaching technique. Their materials had porosity ranging from 47.8 % to 70.9 %, depending on the space holder size (500 μm to 1200 μm). Murakami et al. [11] produced iron foams using CO and CO2 as foaming gases; their maximum porosity was 55 %, and an average pore was 500 μm in size. These processes, however, involved powder compaction, which had a negative effect on the material structure. The sintered porous Selected Microstructural and Mechanical Properties of Open-Cell Metal Foams Depczyński, W. Wojciech Depczyński* Kielce University of Technology, Faculty of Mechatronics and Mechanical Engineering, Poland