Production Techniques of Metallic Foams in Lightweight Materials

Lightweight materials were needed in many different areas, especially in order to reduce the required energy in areas such as automotive and aerospace industries. Metallic foams attract attention in lightweight material applications due to their unique properties. The pores in its structure provide advantages in many applications, both structural and functional by promising both ultra-lightweight construction, energy absorption, and damping insulation. Production techniques of metallic foams can generally be classified as liquid, solid, gas, and ionic state production according to the physical state of the metal at the beginning of the process. The production technique should be chosen according to the usage area and desired properties of the metallic foam and the suitability in terms of cost and sustainability of production. For this reason, the details of the production techniques should be known and the products that can be obtained and their properties should be understood. In this respect, this chapter emphasizes the production methods from past to present.

Investigation of wear mechanics and behaviour of NiCr metallic foam abradables

Current aero-engine sealing materials are reaching their operating limit, as manufacturers seek more efficient engines with longer service lives. Even when utilised in optimum conditions, current materials have inconsistencies in performance due to variabilities in their microstructure, which lead to undesirable responses and events. As such, a new generation of sealing materials is required. Metallic foams are one such material, given the opportunities that exist to both engineer material properties, and achieve relatively consistent microstructures when compared to the current class of thermally sprayed abradable materials. In this study, the abradability of a nickel (70%)–chromium (30%) (NiCr) alloy foam is investigated, with the role of cell size and filler material considered. Tests are performed on a representative high-speed test rig, where a flat blade is used to simulate an aero-engine incursion event. A series of in situ measurement techniques, such as force, temperature and stroboscopic wear measurements are used to characterise the incursion, with DIC (Digital Image Correlation) techniques also employed to investigate breakdown of the foam. Unfilled foams were shown to lead to high blade wear, with the inclusion of filler materials leading to load transfer and collapse of the foam away from the incursion site, along with improved fracture. Both load transfer and ligament collapse mechanisms were found to promote more favourable rub mechanics at all incursion rates tested.

Preparation of Cast Metallic Foams with Irregular and Regular Inner Structure

The aim of this paper is to summarize the possibilities of foundry methods for the production of metallic foams. At present, there are a number of production technologies for this interesting material, to which increasing attention has been paid in recent years. What is unique about metallic foams is the combination of their physical and mechanical properties. As part of our research, we designed and verified four main methods of metallic foam production by the foundry technology, whose products are metallic foam castings with regular and irregular arrangements of internal cavities. All these methods use materials and processes commonly used in conventional foundry technologies. The main idea of the research is to highlight such technologies for the production of metallic foams that could be provided by manufacturing companies without the need to introduce changes in production. Moreover, foundry methods for the production of metallic foams have the unique advantage of being able to produce even complex shaped parts and can thus be competitive compared to today's established technologies, the output of which is usually only a semi-finished product for further processing. This fact was the main motivation for the research.

A Novel Approach of Heat Rate Enhancement in Rectangular Channels with Thin Porous Layer at the Channel Walls

Heat transfer enhancement is a topic of great interest nowadays due to its different applications in industries. A porous material also known as metallic foam plays a major role in heat enhancement at the expense of pressure drop. The flow in channels demonstrates the usefulness of this technology in heat extraction. In our current study, a porous strip attached to the walls of the channels is proposed as an alternative for heat enhancement. The thickness of the porous strip was varied for different Reynolds numbers. By maintaining a laminar regime and using water as a fluid, we determined an optimum thickness of porous material leading to the highest performance evaluation criterion. In our current study, with the aspect ratio being the porous strip thickness over the channel width, an aspect ratio of 0.2 is found to be the alternative. A 40% increase in heat enhancement is detected in the presence of a porous strip when compared to a clear channel case for a Reynolds number equal to 200, which improves further as the Reynolds number increases accordingly.

Manufacturing and Characterization of Tube-Filled ZA27 Metal Foam Heat Exchangers

This study investigates the heat transfer performance of a novel ZA27 metal foam heat exchanger. An open-celled metal foam is combined with a thin-walled copper tube in a single-step casting process. The heat transfer between two separated water streams flowing through the copper tube and foam, respectively, is measured and compared to an equivalent shell tube heat exchanger arrangement. Heat transfer enhancement of up to 71% and a heat transfer rate exceeding 30 kW are observed and attributed to the increased surface area of the metallic foam. However, overall performance was limited by the inefficient heat transfer between the internal mass stream and the copper tube.